Table of contents

When does a scientific journal become a community?

This is not the question that we explicitly set out to address five years ago when IOP Publishing agreed to launch a new format interdisciplinary journal, Environmental Research Letters (ERL). However, on reflection, that is what ERL has become, and what it needs to continue to explore during its next years of growth and evolution.

The motivation for founding ERL was initially more focused: to alter the mode of publication and review in the diverse, yet linked fields of environmental and resource studies and to ensure new levels of interaction, inclusion and equity, providing the platform for the world-changing research findings published in ERL. The key driver in this conversation was the issue of access. Specifically the situation that too many research findings were produced by, and for, very specific academic 'clubs', and that the opportunity to engage in discussion and debate over important emerging findings about our world was being severely limited by the process of publication in frequently slow-to-publish and tremendously expensive traditional academic journals.

The need for change was, and still is, obvious. Environmental and resource studies have been the fastest growing and most diverse nexus of academic research, private sector concern and public sector action. Universities worldwide are adding academic and extension professorships and staff as well as experiencing increasing student interest in this area at a record pace. Corporate social and environmental sustainability has been changing dramatically and, in lurching fits and starts, a mosaic of environmental regulations—both carrots and sticks—are emerging worldwide. The 'Rio + 20' Earth Summit in June 2012 will be a testament to both the dramatic broadening of this interest, and the frustration about the lack of progress at building strong global institutions to permit international cooperation. This is a clear call for an on-going and evolving process of community building.

ERL sought and continues to seek ways to lead this conversation.

1. Open access and equity

First, all ERL articles and data sets are entirely open access. Once published, the materials are free to all users, affluent and poor, anywhere in the world. This is vital for a number of reasons. Environmental stress, degradation, and the creation of innovative solutions involves a global dialog, where traditional expensive subscription and single article costs, as some journals charge, are a complete barrier to researchers, fledgling entrepreneurs, and the public sector in developing nations and in poor communities. Instead, ERL charges authors a fee, generally covered by research grants. Further, we have been able to waive the open access article charge for authors based in areas of the world where this fee may prove prohibitive, as it can be in many developing countries.

In this open access format, ERL publishes cutting-edge original research letters, commentary-style 'Perspective' pieces and editorial articles. ERL is committed to staying at the forefront of the 'gold standard' for open access publishing of articles and data—something that journals are increasingly taking up—and as new ideas come in as to how to improve this process, we will look to put them into practice.

2. Build a network researching sustainability

Second, a journal that reaches across so many disciplines needs to be a place where results are not only reviewed and published quickly, but are then accessible to a broad audience, and are available for debate and conversation. ERL strives to maintain a 90 day timeline from submission to fully peer-reviewed publication online. This process in particular has only been possible with the incredible support of two groups: (1) the dedication of IOP Publishing and the amazingly talented staff they have been able to identify and recruit to work on ERL, and (2) the journal's Editorial Board. We have a team of Editors made up of the most remarkable researchers in their fields, each of whom have committed to this rapid review process. I have often remarked that my academic dream would be to be on a faculty with this group, and ERL has facilitated that vision both virtually and through our meetings. This group is responsible for both the quality of published articles and the speed of our review process.

Rapid publication of rigorously reviewed short-format articles that in their language and style are widely accessible across disciplines has a huge impact. Young researchers doing innovative cutting-edge work often need to get papers out rapidly, and researchers, both junior and senior, gravitate to a journal where important findings can appear rapidly. The results here have been striking and can be showcased by a selection of highlights, such as:

• Achieved an ISI Impact Factor of 3.049 in 2010.

• An average of over 40 000 downloads per month in 2011.

• Hit 50 000 downloads in January 2012.

• Individual articles published in 2011 were downloaded over 650 times each on average during the same year.

• Submissions are up over 50% in 2011 compared to 2010.

• Citations to ERL content up 80% from 2009 to 2010.

3. Build a network conversation about sustainability

The second part of the community building around sustainability, which ERL is now working to develop, is how to facilitate conversation about ideas that the research articles raise. Several exciting developments have shown that we can, in fact, do this particularly effectively, even in these early stages. As an example, ERL's sister community website, environmentalresearchweb, launched in 2007, publishing news, opinion, commentary, jobs, events and promotion of ERL authors' work. To date there are over 9000 registered users and over 6000 weekly newswire subscribers, popularity that reflects the incredibly high standards and wide accessibility of the expert journalistic content published on the site. environmentalresearchweb provides a discussion and commentary environment, a unique service in itself, and also a specific forum for research published in ERL.

Individual topics often come up that warrant not only single articles, but collections of assessments, and ERL has published focus issues in key areas of environmental science including: tropical deforestation, wind energy, the Deepwater Horizon oil spill and climate engineering. ERL is currently publishing seven high-quality focus issues in cutting-edge areas such as arctic vegetation dynamics and cryospheric changes.

Research letters appearing in ERL have received regular and significant coverage in the wider media, with several major news outlets and agencies choosing to cover ERL research, such as Nature, BBC News, New Scientist, The Guardian, Scientific American, Le Monde and many others.

4.The future community of ERL

The process of community support will take many forms at ERL. The journal is growing—we have published the highest number of articles ever in a single volume in 2011 and are looking to continue this growth through into 2012. ERL had an over 50% increase in submissions from 2010 to 2011.

One initiative to mark the journal's 5th anniversary was the 'Best articles' collection [1]; a nominated compilation of articles showcasing the quality of published work in ERL as well as the subject area breadth. Co-authors of the five winning articles have been awarded free publication in ERL until the end of 2012. We can also see the open access model working, in that our articles are highly downloaded outside of the traditionally strong geographical areas of academia (North America and Western Europe), showing that the journal's readership is geographically diverse with high interest from Asia, South America and Africa.

The journal is committed to progress and innovation; coming soon will be a set of new communication tools and online innovations, including:

• Video abstracts from the start of 2012 (for example, the video commentary published alongside this editorial).

• Enhanced HTML format of the full-text article from 2012 onwards—'Article Evolution', an on-going community feedback-driven project to improve the online delivery of research articles.

• New focus issues covering the latest cutting-edge areas of environmental science, with seven planned focus issues for 2012, including: second-generation biofuels, biodiversity, human health and well-being and environmental risks and migration.

These innovations are improving all the time as a result of community response and feedback, both in terms of rating and critiquing the services that ERL provides, and also in looking for ways that the science-practitioner–implementer–regulator nexus can be strengthened.

On all of these I offer my thanks to the ERL community; readers, authors, Editorial Board Members and many others, and extend a request for further suggested innovations for us to try in the next five-year window.

References

[1] Kammen D and Wright G 2011 'Best article' prize for the 5th anniversary of Environmental Research LettersEnviron. Res. Lett.6 040201

As climate changes, how will terrestrial vegetation respond? Because the fates of many biogeochemical, hydrological and economic cycles depend on vegetation, this question is fundamental to climate change science but extremely challenging to address. This is particularly true in the Arctic, where temperature change has been most acute globally (IPCC 2007) and where potential feedbacks to carbon, energy and hydrological cycles have important implications for the rest of the Earth system (Chapin et al 2000).

It is well known that vegetation is tightly coupled to precipitation and temperature (Whittaker 1975), but predicting the response of vegetation to changes in climate involves much more than invoking the limitations of climate envelopes (Thuiller et al 2008). Models must also consider efficacy of dispersal, soil constraints, ecological interactions, possible CO₂ fertilization impacts and the changing impact of other, more proximal anthropogenic effects such as pollution, disturbance, etc (Coops and Waring 2011, Lenihan et al 2008, Scheller and Mladenoff 2005). Given this complexity, a key test will be whether models can match empirical observations of changes that have already occurred.

The challenge is finding empirical observations of change that are appropriate to test hypothesized impacts of climate change. As climate gradually changes across broad bioclimatic gradients, vegetation condition may change gradually as well. To capture these gradual trends, observations need at least three characteristics: (1) they must quantify a vegetation attribute that is expected to change, (2) they must measure that attribute in exactly the same way over long periods of time, and (3) they must sample diverse communities at geographic scales commensurate with the scale of expected climatic shifts. Observation networks meeting all three criteria are rare anywhere on the globe, but particularly so in remote areas.

For this reason, satellite images have long been used as a means of tracking retrospective changes in Arctic and boreal vegetation. These images are attractive because they are consistent over time, are good at mapping vegetation, are available for areas difficult to reach on the ground, and are of broad geographic extent. In a now-classic study, Myneni et al (1998) used historical reanalysis of AVHRR image data to document changes in vegetation phenology at continental scales in the northern hemisphere, finding patterns of change consistent with impacts of increased growing season in boreal and near-polar regions. The year 2000 launch of the MODIS sensors has allowed even more robust assessment of vegetation change in the Arctic (de Beurs and Henebry 2010) and at global scales (Zhao and Running 2010).

Despite opening a window into vegetation change in the Arctic, these studies provide a relatively coarsely filtered view of change. To track trends occurring before the year 2000, researchers are constrained to the large pixel sizes of the AVHRR instrument (nominally 1 km, but typically 4–8 km for derived datasets). Even the finer grain of MODIS (250 m to 1 km resolution) obscures many important natural and anthropogenically derived spatial patterns. The effects of climate change may exacerbate contrasts in competitive status of different vegetative groups (Klady et al 2011, Pieper et al 2011, Seastedt et al 2004). Resolving mechanisms of response requires empirical observation at the scale of individual vegetative communities.

Thus, the new work of Fraser et al (2011) represents a critical milestone in climate change related monitoring of Arctic vegetation. Their work is important in three ways. First, the authors provide the first spatially explicit, continuous record of long-term trends in Arctic vegetation condition at a pixel resolution of 30 m. Based on Landsat Thematic Mapper (TM) data reaching back to the mid 1980s, the work required the overcoming of several key methodological challenges to build a dataset from which trend data could be extracted. While other studies have used TM data to map change across two to three points in time to evaluate change in boreal or arctic vegetation under climate change (Masek 2001, Ranson et al 2004), the time-series analysis of Fraser et al (2011) allows the detection of subtle trends not typically discernible with two-date comparisons. Second, the findings of Fraser et al confirm that vegetation in the Arctic appears to be responding to warming, particularly winter warming. Their maps represent a basic empirical dataset whose spatial patterns should be replicated by model-based approaches. Third, the comparatively fine resolution of this study relative to previous satellite studies allows Fraser et al to more precisely locate where greening occurs. They note increases in shrub cover, confirming findings from studies that used other approaches to reach similar conclusions (Stow et al 2004, Tape et al 2006). They also find evidence that both shrub and herbaceous growth occurs more in landscape positions already favorable to productive vegetation, such as lower hillslopes and valleys, and less so on uplands. Such findings will certainly factor into discussions of the mechanism by which warming could facilitate vegetative growth in Arctic communities (Forbes et al 2010, Sturm et al 2005).

The work of Fraser et al (2011) also adds to a growing body of work leveraging free Landsat data from the US Geological Survey's (USGS) archive. As the longest-running continuous satellite image dataset for land processes, Landsat data provide unparalleled witness to the enormous changes occurring on Earth since 1972 (Wulder et al 2008). By opening the US holdings of the Landsat archive to all humans on the planet (Woodcock et al 2008), the USGS in 2008 catalyzed a blossoming of approaches to capture and characterize that change (Goodwin et al 2010, Hais et al 2009, Hansen et al 2010, Huang et al 2010, Kennedy et al 2010, Potapov et al 2011, Vogelmann et al 2009). While the USGS archive has been dominated by imagery from the United States, recent efforts by the USGS to repatriate data stored in international archives are adding new historical images to the archive every day. With persistence and the goodwill of collaborating countries, this effort may someday allow analyses similar to that of Fraser et al across broader expanses of the Earth, providing further insights into the mechanisms and manifestations of climate change.

References

Chapin F S et al 2000 Arctic and boreal ecosystems of western North America as components of the climate system Glob. Change Biol.6 211–23

Coops N C and Waring R H 2011 A process-based approach to estimate lodgepole pine (Pinus contorta Dougl.) distribution in the Pacific Northwest under climate change Clim. Change105 313–28

de Beurs K M and Henebry G M 2010 A land surface phenology assessment of the northern polar regions using MODIS reflectance time series Can. J. Remote Sens.36 S87–110

Forbes B C, Fauria M M and Zetterberg P 2010 Russian Arctic warming and 'greening' are closely tracked by tundra shrub willows Glob. Change Biol.16 1542–54

Fraser R H et al 2011 Detecting long-term changes to vegetation in northern Canada using the Landsat satellite image archive Environ. Res. Lett.6 045502

Goodwin N R, Magnussen S, Coops N C and Wulder M A 2010 Curve fitting of time-series Landsat imagery for characterizing a mountain pine beetle infestation Int. J. Remote Sens.31 3263–71

Hais M, Jonášová M, Langhammer J and Kuèera T 2009 Comparison of two types of forest disturbance using multitemporal Landsat TM/ETMC imagery and field vegetation data Remote Sens. Environ.113 835–45

Hansen M C, Stehman S V and Potapov P V 2010 Quantification of global gross forest cover loss Proc. Natl Acad. Sci.107 8650–5

Huang C, Goward S N, Masek J G, Thomas N, Zhu Z and Vogelmann J E 2010 An automated approach for reconstructing recent forest disturbance history using dense Landsat time series stacks Remote Sens. Environ.114 183–98

IPCC 2007 Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change ed Core Writing Team, R K Pachauri and A Reisinger (Geneva: IPCC)

Kennedy R E, Yang Z and Cohen W B 2010 Detecting trends in forest disturbance and recovery using yearly Landsat time series: 1. LandTrendr—Temporal segmentation algorithms Remote Sens. Environ.114 2897–910

Klady R A, Henry G H R and Lemay V 2011 Changes in high Arctic tundra plant reproduction in response to long-term experimental warming Glob. Change Biol.17 1611–24

Lenihan J M, Bachelet D, Neilson R P and Drapek R 2008 Simulated response of conterminous United States ecosystems to climate change at different levels of fire suppression, CO2 emission rate, and growth response to CO₂Glob. Planet. Change64 16–25

Masek J G 2001 Stability of boreal forest stands during recent climate change: evidence from Landsat satellite imagery J. Biogeogr.28 967–76

Myneni R B, Tucker C J, Asrar G and Keeling C D 1998 Interannual variations in satellite-sensed vegetation index data from 1981 to 1991 J. Geophys. Res.—Atmos.103 6145–60

Pieper S J, Loewen V, Gill M and Johnstone J F 2011 Plant responses to natural and experimental variations in temperature in Alpine Tundra, Southern Yukon, Canada, Arct. Antarct. Alp. Res.43 442–56

Potapov P V, Turubanova S and Hansen M C 2011 Regionals-scale boreal forest cover and change mapping using Landsat data composites for European Russia Remote Sens. Environ.115 548–61

Ranson K J, Sun G, Kharuk V I and Kovacs K 2004 Assessing tundra-taiga boundary with multi-sensor satellite data Remote Sens. Environ.93 283–95

Scheller R M and Mladenoff D J 2005 A spatially interactive simulation of climate change, harvesting, wind, and tree species migration and projected changes to forest composition and biomass in northern Wisconsin, USA Glob. Change Biol.11 307–21

Seastedt T R, Bowman W D, Caine T N, McKnight D, Townsend A and Williams M W 2004 The landscape continuum: a model for high-elevation ecosystems Bioscience54 111–21

Stow D A et al 2004 Remote sensing of vegetation and land-cover change in Arctic Tundra Ecosystems Remote Sens. Environ.89 281–308

Sturm M, Schimel J, Michaelson G, Welker J M, Oberbauer S F, Liston G E, Fahnestock J and Romanovsky V E 2005 Winter biological processes could help convert arctic tundra to shrubland BioScience55 17–26

Tape K, Sturm M and Racine C 2006 The evidence for shrub expansion in Northern Alaska and the Pan-Arctic Glob. Change Biol.12 686–702

Thuiller W et al 2008 Predicting global change impacts on plant species' distributions: future challenges Perspect. Plant Ecol. Evol. Syst.9 137–52

Vogelmann J E, Tolk B and Zhu Z 2009 Monitoring forest changes in the southwestern United States using multitemporal Landsat data Remote Sens. Environ.113 1739–48

Whittaker R H 1975 Communities and Ecosystems (New York: Macmillan)

Woodcock C F et al 2008 Free access to Landsat imagery Science320 1011

Wulder M A, White J C, Goward S N, Masek J G, Irons J R, Herold M, Cohen W B, Loveland T R and Woodcock C F 2008 Landsat continuity: issues and opportunities for land cover monitoring Remote Sens. Environ.112 955–69

Zhao M and Running S W 2010 Drought-induced reduction in global terrestrial net primary production from 2000 through 2009 Science329 940–3

In recent years there has been a public debate about whether the rate of global warming has waned, prompting the paper 'Is the climate warming or cooling?' in Geophysical Research Letters by Easterling and Wehner (2009). This question has also attracted attention in wider scientific circles, and in a recent paper in Science, Solomon et al (2010) suggested that a decrease in stratospheric water vapour concentrations has slowed the global surface temperature rate between 2000 and 2009. Yet another study by Kaufmann et al (2011) argued that the 'hiatus' in the global warming coincided with near constant combined anthropogenic and natural forcings. The reason: a declining solar insolation, a shift to La Niña conditions and a rapid growth in short-lived sulfur emissions have masked the effect from rising greenhouse gas concentrations (GHGs).

So, what is new? In the paper 'Global temperature evolution 1979–2010', Foster and Rahmstorf (2011) re-examine the situation. Whereas Kaufmann's group only examined the global temperature record from the Hadley Centre and Climate Research Unit (HadCRUT3; Brohan et al 2006) in the United Kingdom, Foster and Rahmstorf present an analysis of the range of available historical temperature records, both from surface thermometers and satellite-based remote sensing. There is one caveat associated with the analysis that Kaufmann's group carried out, which is that the HadCRUT3 record does not fully capture recent enhanced warming over the Arctic, thereby underestimating the evolution of the true global mean compared with other sources. Other analyses, such as the one from NASA/GISS (GISSTEMP; Hansen et al 2010) and those based on atmospheric models (e.g. Kalnay et al 1996), cover the Arctic region better by interpolating the values surrounding the data void or taking physics into account. These, and independent indices such as sea-ice extent (Kinnard et al 2011), ice melting over Greenland (Mernild et al 2009) and permafrost thawing/warming (Isaksen et al 2007), all point to unusual warm conditions in the Arctic.

Foster and Rahmstorf examine global mean temperature trends after accounting for variations associated with three different naturally occurring phenomena: El Niño–Southern Oscillation, volcanic aerosols and solar variability. They used a similar approach to Lean and Rind (2008), but unlike Solomon et al (2010), they did not account for stratospheric water vapour concentrations. Their findings agree with Kaufmann et al (2011) who argue that this factor plays a minor role. Foster and Rahmstorf did not need to account for anthropogenic sulfur aerosols, as a fairly linear warming trend became discernable once the ENSO, solar activity and volcanism were accounted for.

There is always a risk that multiple regression analysis may misattribute significance to unrelated factors (Benestad and Schmidt 2009), and Foster and Rahmstorf made some efforts to test whether their results could be affected by such spurious effects, making their results more convincing. Unfortunately, this is not always the case for papers in the scientific literature, and sometimes papers appear in journals even if they cannot be justified on scientific grounds (i.e. Wagner 2011). An interesting aside, however, is that similar physical principles implying a warming resulting from higher CO₂ concentrations also are the basis for estimating the temperature from the microwave channels measured by satellite-borne instruments. The fact that Foster and Rahmstorf reconcile the trends seen in the in situ surface and satellite-borne remote sensing data brings out the consistency with the physics believed to be central to global warming.

In my view, Foster and Rahmstorf do not come up with new ground-breaking results, but rather a view that fits in with the tacit knowledge about climate. The most interesting aspect is perhaps the different implications for effects associated with stratospheric water vapour and sulfur aerosols. It is also reassuring to see reasonably good agreement between the different data sources, suggesting both robust results and high credibility of the underlying observations. However, these results are not so reassuring in terms of the implications for our society and the question about where we are heading. In fact, there is increased reason for concern because the analysis suggests a fairly substantial sensitivity to other external conditions, especially if the climate sensitivity is similar for GHGs and other forcings (Benestad and Schmidt 2009).

References

Benestad R E and Schmidt G A 2009 J. Geophys. Res.—Atmos.114 D14101

Brohan P et al 2006 J. Geophys. Res.11 D12106

Easterling D R and Wehner M F 2009 Geophys. Res. Lett.36 L08706

Foster G and Rahmstorf S 2011 Environ. Res. Lett.6 044022

Hansen J et al 2010 Rev. Geophys.48 RG4004

Isaksen K et al 2007 Geophys. Res. Lett.34 L17502

Kalnay E et al 1996 Bull. Am. Meteorol. Soc.77 437–71

Kaufmann R K et al 2011 Proc. Natl Acad. Sci.108 11790–3

Kinnard C et al 2011 Nature479 509–12

Lean J and Rind D H 2008 Geophys. Res. Lett.35 L18701

Mernild S H et al 2009 EOS Trans. Am. Geophys. Union90 13–4

Solomon S et al 2010 Science327 1219

Wagner W 2011 Remote Sens.3 2002–4

Numerous studies indicate that the northern high latitudes are experiencing an unprecedented rate of environmental change, including an increase in air temperatures (e.g. Serreze and Francis 2006), reduction of snow cover (e.g. Brown and Robinson 2011), ecosystem transformations and land cover changes (e.g. Callaghan et al 2011). Many of the potential environmental impacts of global warming in the high latitudes are associated with frozen ground, which occupies about 55% of the unglaciated land area in the northern hemisphere and consists of both permafrost and seasonally frozen ground. Frozen soils have a tremendous impact on hydrologic, climatic and biologic systems. Periodic freezing and thawing promote changes in soil structure, affect the surface and subsurface water cycle, and regulate the availability of nutrients in the soil for plants and biota that depend upon them. Freezing and thawing cycles can affect the decomposition of organic substances in the soil and greenhouse gas exchange between the atmosphere and land surface.

Significant efforts have been devoted to permafrost-related studies, including the establishment of standardized observations (e.g. Romanovsky et al 2010, Shiklomanov et al 2008), modeling (e.g. Riseborough et al 2008), and climate-related feedback processes (e.g. Schuur et al 2008). Despite its vast extent and importance, seasonally frozen ground has received much less attention. One of the major obstacles in assessing changes in seasonally frozen ground is the lack of long-term data. In general, observations on soil temperature and freeze propagation are available for a limited area and involve a relatively short time period, precluding assessment of long-term, climate-driven change. A few known exceptions include shallow soil temperature and freeze/thaw depth observations conducted as part of the standard hydrometeorological monitoring system in China (e.g. Zhao et al 2004) and the Soviet Union/Russia (e.g. Gilichinsky et al 2000).

In their recent paper entitled 'An observational 71-year history of seasonally frozen ground changes in Eurasian high latitudes', Frauenfeld and Zhang (2011) provided detailed analysis of soil temperature data to assess 1930–2000 trends in seasonal freezing depth. The data were obtained from 387 Soviet non-permafrost meteorological stations. The authors performed systematic, quality-controlled, integrative analysis over the entire former Soviet Union domain. The long-term changes in depth of seasonal freezing were discussed in relation to such forcing variables as air temperature, degree days of freezing/thawing, snow depth and summer precipitation as well as modes of the North Atlantic Oscillation. The spatially average approach adopted for the study provides a generalized continental-scale trend. The study greatly improves, expands and extends previous 1956–90 analysis of the ground thermal regime over the Eurasian high latitudes (Frauenfeld et al 2004).

Although the work of Frauenfeld and Zhang (2011) is the most comprehensive assessment of the continental-scale long-term trends in seasonal freezing available to date, more detailed analysis is needed to determine the effect of climate change on seasonally frozen ground. It should be noted that, in addition to the variables considered for analysis, other non-climatic factors affect the depth of freezing propagation. Unlike the surface, which is influenced by the climate directly, the ground even at shallow depth receives a climatic signal that is substantially modified by edaphic processes, contributing to highly localized thermal sensitivities of the ground to climatic forcing. Subsurface properties, soil moisture, and snow and vegetation covers influence the depth of freezing. Topography also plays an important role in establishing the ground thermal regime. It is an important determinant of the amount of heat received by the ground surface, affects the distribution of snow and vegetation, and influences the surface and subsurface moisture regimes. As a result, the ground temperature and the related depth of freezing propagation are characterized by very high variability over short lateral distances.

The data used for analysis by Frauenfeld and Zhang are single-point measurements obtained from a network of stations sparsely distributed over a very large spatial domain. Since no variability in edaphic conditions was considered, the presented results should be interpreted with some degree of caution. In addition, long-term soil observations at a single point using unautomated techniques unavoidably cause site disturbance, which may significantly modify the ground thermal regime over time.

I would like to emphasize that the generalized continental trend in the depth of seasonal freezing presented by Frauenfeld and Zhang is very likely associated with changes in atmospheric forcing. However, any long-term continental trends of such a spatially heterogeneous and sensitive parameter as shallow soil temperature potentially include a significant non-climatic component. Although the single-point temperature data used by Frauenfeld and Zhang might not be sufficient to fully evaluate the localized effects on the overall trend, they are a terrific asset for further studies on climate and ground thermal regime. Detailed spatial assessment of the available ground temperature records over relatively homogeneous regions is a necessary next step in the assessment of climate-induced changes in seasonally frozen ground. Such an analysis is likely to show significant regional differences in long-term freeze propagation trends over Northern Eurasia and reveal region-specific sensitivities of the ground thermal regime to climatic forcing.

References

Brown R D and Robinson D A 2011 Northern hemisphere spring snow cover variability and change over 1922–2010 including an assessment of uncertainty Cryosphere5 219–29

Callaghan T V, Tweedie C E and Webber P J 2011 Multi-decadal changes in tundra environments and ecosystems: the International Polar Year-Back to the Future Project (IPYBTF) AMBIO40 555–7

Frauenfeld O W and Zhang T 2011 An observational 71-year history of seasonally frozen ground changes in the Eurasian high latitudes Environ. Res. Lett.6 044024

Frauenfeld O W, Zhang T, Barry R G and Gilichinsky D 2004 Interdecadal changes in seasonal freeze and thaw depths in Russia J. Geophys. Res.109 D5101

Gilichinsky D A et al 2000 Use of the data of hydrometeorological survey for century history of soil temperature trends in the seasonally frozen and permafrost areas of Russia Earth Cryosp.4 59–66 (in Russian)

Riseborough D, Shiklomanov N I, Etselmuller B and Gruber S 2008 Recent advances in permafrost modeling Permafr. Pereglac. Process.19 137–56

Romanovsky V E et al 2010 Thermal state of permafrost in Russia Permafr. Periglac. Process.21 136–55

Schuur E A G et al 2008 Vulnerability of permafrost carbon to climate change: implications for the global carbon cycle Bioscience58 701–14

Serreze M C and Francis J A 2006 The Arctic amplification debate Clim. Change76 241–64

Shiklomanov N I, Nelson F E, Streletskiy D A, Hinkel K M and Brown J 2008 The circumpolar active layer monitoring (CALM) program: data collection, management, and dissemination strategies Proc. of the 9th International Conf. on Permafrost (Fairbanks, AK, 29 June–3 July 2008) vol 1, pp 1647–52

Zhao L, Ping C L, Yang D, Cheng G, Ding Y and Liu S 2004 Changes of climate and seasonally frozen ground over the past 30 years in Qinghai-Xizang (Tibetan) Plateau, China Glob. Planet. Change43 19–31

The cryosphere consists of water in the solid form at the Earth's surface and includes, among others, snow, sea ice, glaciers and ice sheets. Since the 1990s the cryosphere and its components have often been considered as indicators of global warming because rising temperatures can enhance the melting of solid water (e.g. Barry et al 1993, Goodison and Walker 1993, Armstrong and Brun 2008). Changes in the cryosphere are often easier to recognize than a global temperature rise of a couple of degrees: many locals and tourists have hands-on experience in changes in the extent of glaciers or the duration of winter snow cover on the Eurasian and North American continents.

On a more scientific basis, the last IPCC report left no doubt: the amount of snow and ice on Earth is decreasing (Lemke et al 2007). Available data showed clearly decreasing trends in the sea ice and frozen ground extent of the Northern Hemisphere (NH) and the global glacier mass balance. However, the trend in the snow cover extent (SCE) of the NH was much more ambiguous; a result that has since been confirmed by the online available up-to-date analysis of the SCE performed by the Rutgers University Global Snow Lab (climate.rutgers.edu/snowcover/).

The behavior of snow is not the result of a simple cause-and-effect relationship between air temperature and snow. It is instead related to a rather complex interplay between external meteorological parameters and internal processes in the snowpack. While air temperature is of course a crucial parameter for snow and its melting, precipitation and radiation are also important. Further physical properties like snow grain size and the amount of absorbing impurities in the snow determine the fraction of absorbed radiation. While all these parameters affect the energy budget of the snowpack, each of these variables can dominate depending on the season or, more generally, on environmental conditions. As a result, the reduction in SCE in spring and summer in the NH was attributed to faster melting because of higher air temperatures, while the winter months (December to February) saw an increase in the SCE due to increased precipitation (Lemke et al >2007).

Cohen et al (2012) confirmed these opposing effects in the SCE and showed that on the Eurasian continent the average SCE in October has increased by approximately 3 × 10⁶ km² in the last two decades; a growth of almost 40%, corresponding to roughly 1.5 times the area of Greenland. For the same period, Cohen et al (2012) found a negligible trend in the average temperatures above the continents of the NH for the winter months despite a significant increase in the annual mean temperature for the same regions. Cohen et al (2012) propose the following link between temperatures and snow: the reduced sea ice cover of the Arctic Ocean and the enhanced air temperatures in fall cause higher evaporation from the Arctic Ocean, leading to increased tropospheric moisture in the Arctic. More moisture results in more snowfall over the Eurasian continent, increasing the SCE. The increased snow cover strengthens the Siberian High, a strong anticyclonic system generally persistent between October and April. This system is strong enough to affect weather patterns in large parts of the NH, resulting in changes in the large-scale circulation of the NH (Panagiotopoulos et al 2005). As a result, outbreaks of cold Arctic air masses into the mid-latitudes are more frequent, leading to low temperatures over the eastern part of North America and Northern Eurasia. According to Cohen et al (2012), these are exactly the same regions that have experienced a cooling trend in the winter temperature over the past twenty years.

While this chain of events is plausible (and some are confirmed by observations), existing climate models are not yet capable of reproducing these processes. On the contrary, Cohen et al (2012) showed that they predict a slightly decreasing SCE in October for Eurasia and an increase in winter temperatures over the continents in the NH. This is not surprising because the simulation of snow and its interactions with the atmosphere in global models is imperfect (Armstrong and Brun 2008). Most models have difficulty in simulating successfully the complex behavior of snow cover. A better representation of snow in the models is vital in order to understand the possible far-reaching consequences of changes in the SCE and its effects on the local climate and on large-scale circulations in the atmosphere to utilize snow as a reliable indicator for a changing climate. However, the SCE is only one of many possible snow parameters that can be used (Goodison and Walker 1993). Although omni-present in many regions and during many seasons, there is still much to be learned about snow and how it is linked to the global climate system.

References

Armstrong R L and Brun E 2008 Snow and Climate: Physical Processes, Surface Energy Exchange and Modeling (Cambridge: Cambridge University Press)

Barry R G, Goodison B E and LeDrew E F (ed) 1993 Snow watch '92—detection strategies for snow and ice Glaciological Data Report GD-25 (Boulder, CO: World Data Center A: Glaciology (Snow and Ice)) p 273

Cohen J L, Furtado J C, Barlow M A, Alexeev V A and Cherry J E 2012 Arctic warming, increasing snow cover and widespread boreal winter cooling Environ. Res. Lett.7 014007

Goodison B E and Walker A E 1993 Use of snow cover derived from satellite passive microwave data as indicator for climate change Ann. Glaciol.17 137–42

Lemke P et al 2007 Observations: changes in snow, ice and frozen ground Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge: Cambridge University Press)

Panagiotopoulos F, Shahgedanova M, Hannachi A and Stephenson D B 2005 Observed trends and teleconnections of the Siberian high: a recently declining center of action J. Clim.18 1411–22

Arctic tundra ecosystems stand to play a substantial role in both the magnitude and rate of global climate warming over the coming decades and centuries. The exact nature of this role will be determined by the combined effects of currently amplified rates of climate warming in the Arctic (Serreze et al 2000) and a series of related positive climate feedbacks that include mobilization of permafrost carbon (Schuur et al 2008), decreases in surface albedo (Chapin et al 2005) and evapotranspiration (ET) mediated increases in atmospheric water vapor (Swann et al 2010). Conceptually, these feedback mechanisms are intuitive and readily comprehensible: warming-induced permafrost thaw will make new soil carbon pools accessible for microbial respiration, and increased vegetation productivity, expansion of shrubs in particular, will lower surface reflectance and increase ET. However, our current understanding of these feedback mechanisms relies largely on limited and local field studies and, as such, the quantitative estimates of feedback effects on regional and global climate require spatial upscaling and uncertainty estimates derived from models. Moreover, the feedback mechanisms interact and their combined net effect on climate is highly variable and not well characterized.

A recent study by Bonfils et al (2012) is among the first to explicitly examine how shrub expansion in tundra ecosystems will impact regional climate. Using an Earth system model, Bonfils et al find that an idealized 20% increase in shrub cover north of 60°N latitude will lead to annual temperature increases of 0.66 °C and 1.84 °C, respectively, when the shrubs are 0.5 m and 2 m tall. The modeled temperature increases arise from atmospheric heating as a combined consequence of decreased albedo and increased ET. The primary difference between the two cases is associated with the fact that tall shrubs protrude above the snow, thus reducing albedo year round, whereas short shrubs are completely covered by the snowpack for part of the year.

These results support evidence that shrub expansion in Arctic tundra will feed back positively to ongoing climate warming but, perhaps more importantly, illustrate the significance of shrub height in dictating the feedback strength. While differences in albedo associated with vegetation stature have been previously documented in these ecosystems (Loranty et al 2011, Sturm et al 2005a), the magnitudes of the feedbacks on regional climate were unknown. These findings highlight a pressing need to understand the rate and spatial extent at which shrub expansion is occurring. While increases in vegetation productivity inferred from satellite data have been observed across the Arctic (Bunn and Goetz 2006, Goetz et al 2005, Walker et al 2009), recent analyses suggest that the observed trends are a result of general increases in productivity across all vegetation types (Beck and Goetz 2011).

Another important finding reported by Bonfils et al (2012) is the positive correlation between shrub height and modeled active layer depth (i.e. permafrost thaw). Results from a field study (Blok et al 2010) showed that the shading effects of shrub canopies reduce ground heat flux, which in turn leads to a decrease in active layer depth. Bonfils et al's (2012) results indicate that regional warming as a consequence of albedo and ET feedbacks will offset the local cooling effects of increased shrub cover, thus the net climate feedback associated with shrub expansion could be greater than reported (owing to biogeochemical processes and related feedbacks). A similar study by Lawrence and Swenson (2011) found that snow redistribution to shrub covered areas (Sturm et al 2005b) simultaneously reduced the albedo feedback by covering shrubs with snow and introduced a soil warming feedback through insulation provided by additional snow cover, with a net result of increased active layer depth under shrubs. When shrub cover (1 m tall canopy) was increased by 20% and less snow was available for redistribution over a greater shrub covered area, the insulation effect was not great enough to offset the reduction in albedo, thus on average the effect of shrub cover on active layer depth was negligible. These results underscore the importance of shrub height, shrub cover and snow depth when considering how shrub expansion will influence net feedbacks to climate.

Uncertainties regarding the interacting effects of snow redistribution and albedo feedbacks on active layer depth make it difficult to predict how shrub expansion may ultimately mediate permafrost feedbacks to climate on annual to decadal timescales. Although both Bonfils et al (2012) and Lawrence and Swenson (2011) provide strong evidence that the albedo and ET feedbacks associated with a 20% increase in shrub cover, relative to the current distribution, will result in warming that more than offsets local cooling, the effects of a 5% or 10% increase in shrub cover are less clear. For example, it may be reasonable to assume that a 20% increase in shrub cover over the next 100 years will lead to a 1.84 °C regional temperature increase and, consequently, substantial permafrost thaw. But will a 0.46 °C increase over the next 25 years with a 5% increase in shrub cover significantly increase the active layer depth or melt permafrost? The regional warming associated with a 5% increase in shrub cover may not be strong enough to counteract the local cooling effects of shrubs (Blok et al 2010), in which case increased shrub cover could serve as a negative feedback to permafrost thaw in the near term, retarding the process, or even promoting permafrost aggradation. On the other hand, it is possible that the greater snow redistribution that would occur with less shrub cover (Lawrence and Swenson 2011) could lead to higher rates of winter warming that would offset the local cooling effects caused by shading during the growing season, thereby acting as a positive feedback to permafrost thaw. These feedbacks could either mitigate or exacerbate permafrost degradation associated with ongoing climate warming; thus research on this subject is essential and timely given the rates of shrub cover change documented by historical photographs (Tape et al 2006) and satellite imagery (Forbes et al 2010).

A complete understanding of the net climate feedback effects of shrub expansion in Arctic tundra will require improved knowledge of the factors controlling shrub distribution and the associated vegetation structure influences on the redistribution of snow. A recent synthesis highlights the myriad complex and interacting factors that are likely to govern shrub expansion, which include recruitment and dispersal mechanisms, species differences, topo-edaphic factors, and the role of disturbance and biotic interactions (Myers-Smith et al 2011). In the context of understanding climate feedbacks, it is imperative that future studies distinguish between instances of shrub expansion that include an increase in canopy height or extent that is biophysically relevant. Increased effort is needed to understand snow–shrub interactions in the context of surface energy fluxes. This level of detail is necessary for accurate prediction of the rate and magnitude of shrub mediated climate feedbacks in the Arctic.

Acknowledgment

We thank Ken Tape for insightful discussion that helped to improve this manuscript.

References

Beck P S A and Goetz S G 2011 Satellite observations of high northern latitude vegetation productivity changes between 1982 and 2008: ecological variability and regional differences Environ. Res. Lett.6 045501

Blok D, Heijmans M, Schaepman-Strub G, Kononov A, Maximov T and Berendse F 2010 Shrub expansion may reduce summer permafrost thaw in Siberian tundra Glob. Change Biol.16 1296–305

Bonfils C J W, Phillips T J, Lawrence D M, Cameron-Smith P, Riley W J and Subin Z M 2012 On the influence of shrub height and expansion on northern high latitude climate Environ. Res. Lett.7 015503

Bunn A G and Goetz S J 2006 Trends in satellite-observed circumpolar photosynthetic activity from 1982 to 2003: the influence of seasonality, cover type, and vegetation density Earth Interact.10 12

Chapin F et al 2005 Role of land-surface changes in Arctic summer warming Science310 657

Forbes B C, Fauria M M and Zetterberg P 2010 Russian Arctic warming and greening are closely tracked by tundra shrub willows Glob. Change Biol.16 1542–54

Goetz S J, Bunn A G, Fiske G and Houghton R 2005 Satellite-observed photosynthetic trends across boreal North America associated with climate and fire disturbance Proc. Natl Acad. Sci. USA102 13521–5

Lawrence D M and Swenson S C 2011 Permafrost response to increasing Arctic shrub abundance depends on the relative influence of shrubs on local soil cooling versus large-scale climate warming Environ. Res. Lett.6 045504

Loranty M M, Goetz S J and Beck P S A 2011 Tundra vegetation effects on pan-Arctic albedo Environ. Res. Lett.6 024014

Myers-Smith I H et al 2011 Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities Environ. Res. Lett.6 045509

Schuur E et al 2008 Vulnerability of permafrost carbon to climate change: implications for the global carbon cycle BioScience58 701–14

Serreze M, Walsh J, Chapin F, Osterkamp T, Dyurgerov M, Romanovsky V, Oechel W, Morison J, Zhang T and Barry R 2000 Observational evidence of recent change in the northern high-latitude environment Clim. Change46 159–207

Sturm M, Douglas T, Racine C and Liston G 2005a Changing snow and shrub conditions affect albedo with global implications J. Geophys. Res.110 G01004

Sturm M, Schimel J, Michaelson G and Welker J M 2005b Winter biological processes could help convert Arctic tundra to shrubland BioScience55 17–26

Swann A L, Fung I Y, Levis S, Bonan G B and Doney S C 2010 Changes in Arctic vegetation amplify high-latitude warming through the greenhouse effect Proc. Natl Acad. Sci.107 1295–300

Tape K, Sturm M and Racine C 2006 The evidence for shrub expansion in Northern Alaska and the Pan-Arctic Glob. Change Biol.12 686–702

Walker D, Leibman M, Epstein H, Forbes B, Bhatt U, Raynolds M, Comiso J, Gubarkov A, Khomutov A and Jia G 2009 Spatial and temporal patterns of greenness on the Yamal Peninsula, Russia: interactions of ecological and social factors affecting the Arctic normalized difference vegetation index Environ. Res. Lett.4 045004

I first came across Carey King when, out of the blue, he invited me to a special session of the annual meeting of the American Association for the Advancement of Science (the largest and most prestigious US scientific meeting) where he was developing a special session on energy return on investment (EROI). At that meeting and since, I have found Carey to be a refreshing new colleague, extremely intelligent, very knowledgeable about many diverse aspects of energy and other things, able to take criticism and to dish it out, and very ambitious, which is mostly a good thing. He is becoming a leader in thinking about EROI and its implications, and I am delighted to see him honored by Environmental Research Letters.

This is important because in the US, there is little insight about energy or, especially, its potential physical limitations except when gas prices increase. There is also little awareness of the very strong historical connection in both the US and the world between increased affluence and increased use of energy, especially petroleum. It is not understood by all that many of the economic problems we have now (such as the budgetary problems faced by most of our State governments, pension plans and universities) have substantial origin in the fact that oil and other energy production no longer increase reliably year after year, as they once did (Murphy and Hall 2011). Many economists have argued in the past that energy is not important because it constituted only 5 per cent or so of GDP, or because they believe that market forces and innovations will substitute for any shortage (e.g. Barnett and Morse 1963, Passell et al 1972, Solow 1974, Denison 1989). One problem with that view is that if you remove that five per cent the economy comes to a dead stop, as Cuba found out in 1989 when Russia removed its oil subsidy. Additionally if that five per cent goes up to 10 or 15 per cent, as it did in the early 1980s, and again in 2008, recession steps in (Murphy and Hall 2011). In fact, the US economy and our energy use increased almost lockstep from 1900 until 1984 (Cleveland et al 1984). The economy has grown more rapidly than energy use since 1984. Most economists think that this is due to our cleverness at increasing efficiency, but Robert Kaufmann (2004) and others find that instead most of the increase has been due to, essentially, the outsourcing of our heavy industry (think steel imported from Korea or Brazil, petroleum refined in Trinidad etc). An additional issue is that there is considerable evidence (e.g. Shadow Government Statistics) that the official US government inflation corrections have been deliberately underestimated since about 1985. If this is true then GDP growth has been exaggerated and there has been little or no increase in efficiency. Thus our gain in actual national energy efficiency is probably much less than most economists believe, and may be close to zero.

Obviously some few of us think a great deal about energy, and for those who are willing to undertake some personal research (for example on the ASPO (aspo-usa.com) or The Oil Drum (www.theoildrum.com) websites), there is much to be concerned about. First on the list of concerns is 'peak oil'; the concept that there comes a time over the life cycle of the extraction of a non-renewable resource when there will be maximum production. This concept, derived by geologist M K Hubbert in the 1950s, assumes that this peak will occur when roughly 50 per cent of the resource has been exploited. Hubbert famously predicted in 1955 that this would occur for the United States in 1970. Initially he was derided by most in the oil industry, but in fact peak oil for the US did occur in 1970, just as he had predicted. Oil production has declined essentially every year since then. 'Peak oil' has now occurred for something like three quarters of all oil producing nations, although not yet for most of the largest producers.

Second on my list of energy concerns is declining EROI. EROI is a term I had developed in the early 1980s based on the net energy concepts of Howard Odum (Odum 1973, Hall 1972). It is simply the ratio of the energy returned from an energy extraction process divided by the energy to get that energy. The concept had a certain amount of traction in the 1980s (Hall and Cleveland 1981, Cleveland et al 1984) but as gasoline prices fell and memories of the 'energy crises' of the 1970s faded, interest in energy matters also declined. A few of us 'energy nuts' kept plugging away at trying to get better numbers (Hall and Klitgaard 2011).

In contrast to most people and certainly most economists, Carey King is someone who has thought about energy, peak oil and EROI a lot, and in very sophisticated ways. Early in his career Carey deduced that EROI appeared to be having a new day because of, for example, questions about the EROI of corn-based ethanol for transportation fuels and because of the declining productivity and profitability of many Texas and other oil fields. For many, including Carey and myself, it made no sense to trade one Joule of fossil energy to run tractors, make fertilizers, distill mash and so on to generate about one Joule of corn-based ethanol, which the US is doing on a vast, federally-subsidized scale. Carey has had some quite original ideas about coming up with a shortcut to deriving a proxy measurement for EROI, which is quite difficult to calculate, and about the importance of EROI for financial issues. For example Carey has found that the inflation-adjusted prices of oil and coal are basically predicable over the last century from the EROI at that time (King 2010). He has also worked with others at attempting to get at a more comprehensive EROI that would include the energy cost of supporting all of the money spent developing the resource, including the energy associated with giving meaning to laborers' pay checks and the energy associated with financial services. We do not yet understand the importance of these more comprehensive EROIs but we do understand that our usual methods of including only energy used directly (e.g. to run a pump) or indirectly (e.g. to manufacture the steel forms used) greatly underestimates the total amount of energy needed to produce energy.

In conclusion, Carey King appears to be one of the real rising energy stars as energy becomes again much more important. He is very bright, original and is a very hard worker. I look forward to much exciting, innovative and important work from his endeavors.

References

Barnett H and Morse C 1963 Scarcity and Growth: The Economics of Natural Resource Availability (Baltimore, MD: Johns Hopkins Press)

Cleveland C J, Costanza R, Hall C A S and Kaufmann R 1984 Energy and the United States economy: a biophysical perspective Science225 890–7

Denison E F 1989 Estimates of Productivity Change by Industry, an Evaluation and an Alternative (Washington, DC: The Brookings Institution)

Hall C A S 1972 Migration and metabolism in a temperate stream ecosystem Ecology53 585–604

Hall C A S and Cleveland C J 1981 Petroleum drilling and production in the United States: yield per effort and net energy analysis Science211 576–9

Hall C A S and Klitgaard K 2011 Energy and the Wealth of Nations: Understanding the Biophysical Economy (New York: Springer)

Kaufmann R 2004 The mechanisms for autonomous energy efficiency increases: a cointegration analysis of the US Energy/GDP Ratio The Energy Journal25 63–86

King C W 2010 Energy intensity ratios as net energy measures of United States energy production and expenditures Environ. Res. Lett.5 044006

Murphy D J and Hall C A S 2011 Energy return on investment, peak oil, and the end of economic growth in 'Ecological Economics Reviews' ed Robert Costanza, Karin Limburg and Ida Kubiszewski Ann. N.Y. Acad. Sci.1219 52–72

Solow R M 1974 The economics of resources or the resources of economics American Economic Review66 1–14

Odum H T 1973 Environment, Power and Society (New York: Wiley Interscience)

Passell P, Roberts M and Ross L 1972 Review of 'Limits to Growth' New York Times Book Review 2 April 1972

Our knowledge of how agriculture expands, and the types of land it replaces, is remarkably limited across the tropics. Most remote-sensing studies focus on the net gains and losses in forests and agricultural land rather than the land-use transition pathways (Gibbs et al 2010). Only a handful of studies identify land sources for new croplands or plantations, and then only for farming systems aggregated together (e.g., Koh and Wilcove 2008, Morton et al 2006, Gibbs et al 2010). Gutiérrez-Vélez et al (2011), however, have taken a leap forward by tracking the different expansion pathways for smallholder and industrial oil palm plantations.

Using a combination of Landsat, MODIS and field surveys, they investigate whether higher yields in new agricultural lands spare forests in the Peruvian Amazon and in a smaller focus area in the Ucayali region. Across the Peruvian Amazon, they show that between 2000 and 2010, new high-yield oil palm plantations replaced forests 72% of the time and accounted for 1.3% of total deforestation, with most expansion occurring after 2006.

Gutiérrez-Vélez et al went further in the Ucayali region and compared land sources for new high-yield and low-yield plantations. Expansion of higher-yield agricultural lands should logically reduce the total area needed for production, thus potentially sparing forests. In the Ucayali focus area, expansion of high-yield oil palm did convert less total land area but more forest was cleared than with low-yield expansion. Smaller-scale plantations tended to expand into already cleared areas while industrial-scale plantations traded their greater yields for forests, leading to higher land-clearing carbon emissions per production unit (Gibbs et al 2008). Gutiérrez-Vélez et al show that higher yields may require less land for production but more forest may be lost in the process, and they emphasize the need for stronger incentives for land sparing. The potential land-saving nature of these high-yield plantations could be further analyzed by considering whether they help depress global prices, reducing incentives to expand elsewhere (Angelsen and Kaimowitz 2001).

The significance of the study goes well beyond the bounds of Ucayli, and highlights risks to Amazonian forests from oil palm expansion (Butler and Laurance 2010). Oil palm is an astoundingly profitable and productive crop, with typical oil yields more than ten times that of soy. Some have even argued that oil palm is innately land sparing because it would take substantially more land for all other oil-bearing crops to provide the same output. However, most production gains from oil palm have occurred through increased area rather than increased yield, and in many cases expansion has been through forest clearing (Koh and Wilcove 2008, Gibbs et al 2010). The findings of Gutiérrez-Vélez et al (2011) are particularly significant considering that the booming palm oil sectors in Indonesia and Malaysia, which currently produce over 80% of the world's product, are facing a host of pressures that constrain future area expansion. Malaysia has little remaining land suited for plantations and Indonesia faces intensifying international scrutiny over the future of their forestlands. Consequently, the Amazon basin is widely considered the new frontier, with more than half of its forest area suitable for palm oil cultivation (Butler and Laurance 2010) and growing incentives from Brazil's Program for the Sustainable Production of Oil Palm, which aims to utilize degraded lands and spur reforestation efforts.

Their results also illuminate another key issue, namely the constraints faced by large-scale producers when they seek to expand plantation area. Emerging demand-side conservation efforts, such as the Roundtable for Sustainable Palm Oil (RSPO), assume that already cleared and non-forested lands are freely available. Gutiérrez-Vélez et al (2011) hint at the obstacles to using such cleared lands, which is that they are inhabited and often have contested land tenure. We must carefully consider our consumption of these commodities in the face of growing land scarcity (Lambin and Meyfroidt 2011). If high-yield plantations displace low-yield plantations they too may follow the path of industrial agriculture and resume destruction of the forests that conservation efforts aim to protect. Without clear incentives to spare land, we could be trading forest for higher yields.

References

Angelsen A and Kaimowitz D 2001 Agricultural Technologies and Tropical Deforestation (New York: CABI Publishing) (www.cifor.org/publications/pdf files/books/bangelsen0101e0.pdf)

Butler R and Laurance W 2010 Is oil palm the next emerging threat to the Amazon? Trop. Conserv. Sci.2 1–10

Gibbs H K, Johnston M, Foley J A, Holloway T, Monfreda C, Ramankutty N and Zaks D 2008 Carbon payback times for crop-based biofuel expansion in the tropics: the effects of changing yield and technology Environ. Res. Lett.3 034001

Gibbs H K, Ruesch A S, Achard F, Clayton M K, Holmgren P, Ramankutty N and Foley J A 2010 Tropical forests were the primary sources of new agricultural land in the 1980s and 1990s Proc. Natl Acad. Sci.107 16732–7

Gutiérrez-Vélez V H, DeFries R, Pinedo-Vásquez M, Uriarte M, Padoch C, Baethgen W, Fernandes K and Lim Y 2011 High-yield oil palm expansion spares land at the expense of forests in the Peruvian Amazon Environ. Res. Lett.6 044029

Koh L and Wilcove D 2008 Is oil palm agriculture really destroying tropical biodiversity? Conserv. Lett.1 60–4

Lambin E and Meyfroidt P 2011 Inaugural article: global land use change, economic globalization, and the looming land scarcity Proc. Natl Acad. Sci.108 93465–72

Morton D C et al 2006 Cropland expansion changes deforestation dynamics in the southern Brazilian Amazon Proc. Natl Acad. Sci. USA103 14637–41

In November 2011, botanists on a remote island off Papua New Guinea discovered a new species of orchid—uniquely and mysteriously night-flowering [1]. New to science, and with so much more to understand, this flower is threatened by deforestation [2]. Also in November 2011, a survey of 583 conservation scientists reported a unanimous (99.5%) view that 'it is likely a serious loss of biological diversity is underway at a global extent' and that, for scientists, 'protection of biological diversity for its cultural and spiritual values and because of its usefulness to humans were low priorities, which suggests that many scientists do not fully support the utilitarian concept of ecosystem services' [3]. In terms of management, some scientists now advocate controversial conservation strategies such as triage (prioritization of species that provide unique or necessary functions to ecosystems) [4, 5].

Meanwhile, there are many scientists who contend that there is an urgent need to improve our understanding of the importance of biodiversity for human health and well-being, arguing that only an anthropocentric view of biodiversity within a paradigm 'ecosystem service' will enable decision-makers to prioritize the theme [6–9]. A 2011 UN report argues that this need for understanding is especially urgent in fragile and vulnerable ecosystems where communities depend directly on the resources of their environment [10].

Here we have a paradox: international conservation scientists think that we cannot protect biodiversity on the basis of its cultural and spiritual value, nor its usefulness to humans. Other scientists argue that using a utilitarian ecosystem services framework is the only way to get humans to protect biodiversity. Meanwhile, communities directly dependent on biodiverse ecosystems are often those who best understand and protect biodiversity, for exactly these reasons of use and spiritual connection, but they do not hold only a utilitarian view of their environment and its diversity. These communities often define their own 'health' as integrally linked to the 'health' of the ecosystem, and they see themselves as an integral part of the ecosystem [11].

It is generally accepted that the destruction of biodiverse ecosystems internationally is not by communities directly dependent on these ecosystems, but from processes such as deforestation, mining, resource extraction and biopiracy, generated by external human demand [12–16]. Rich countries and their populations are currently particularly responsible for the resource extraction that impacts negatively on biodiversity and on the well-being of local communities [17]. However, increasingly, urban populations in every country demand resources and products from biodiverse regions, and with rising urban populations this threat is likely to increase.

To illustrate, we can take one example. Amazonia is one of Earth's most important biodiverse tropical moist forest ecosystems. As the Amazonian forest reaches the Andes it becomes a contiguous and equally vital ecosystem: the Yungas or Cloud Forest [18]. These two sister forests are amongst the most biodiverse ecosystems of the world, spanning several Latin American countries (including Brazil, Argentina, Peru, Bolivia, Venezuela, Colombia and Ecuador), and over 7 million square kilometres [18, 19]. For millennia, across modern geopolitical boundaries, Amazonia/Yungas has been protected by over 1000 different indigenous peoples [20]. In turn, Amazonia/Yungas has provided health and spiritual well-being for indigenous peoples via food, medicines, home and culture [21]. Using a utilitarian view of the ecosystem, these forests also provide the world with some of its most important ecosystem services in terms of forest and food resources, current and potential new medicines, rainfall regulation and a global carbon sink [19, 22].

In terms of protection of these ecosystems, there is evidence that recognized 'indigenous territories' within Amazonia/Yungas are better protected, in terms of biodiversity and environmental damage, than other conservation units such as national or regional reserves [23, 24]. Yet deforestation, resource extraction and climate change threaten all parts of the Amazonia/Yungas [19, 25–28], and indigenous communities, amongst the most marginalized peoples in Latin America [29], are experiencing increasing threats to their territories, and their health and well-being [20]. Figures 1–3 show different aspects of the Andean Yungas and high mountain ecosystems of Argentina. The ecosystems are highly biodiverse. We are only beginning to understand the extent of their importance for human well-being, and these incredible forests are at risk from deforestation, mining and climate change.

Figure 1. Rio Cochuna in Tucumán, Argentina, part of the vital and extensive river system of the Andean Yungas, home to amazing and underexplored biodiversity. By Carolyn Stephens.

Figure 2.Argiope argentata—widespread and striking, this spider can eat twice her weight in insects and her venom is thought to have medicinal properties. By Carolyn Stephens.

Figure 3. Humming birds may not seem to have a direct ecosystem service, but they, along with many insect species, are important pollinators of plants and trees which themselves may be directly important for human health. By Alfredo Gutierrez.

It is notable that, recognizing their vital role in ecosystem understanding protection, indigenous peoples and local communities now play an important part in global policy processes, including the United Nations Convention on Biological Diversity (CBD) and the UN Framework Convention on Climate Change (UNFCCC) [30]. In 2011, the IUCN met with indigenous representatives and conservation organizations to discuss conservation priorities in the context of indigenous rights. IUCN agreed to review the implementation of resolutions related to indigenous peoples taken at the 4th World Conservation Congress (WCC4) in 2008, and to advance their implementation. These resolutions, along with the Durban Action Plan and the Programme of Work on Protected Areas of the United Nations Convention on Biological Diversity (CBD), are often termed as the 'new conservation paradigm' [31].

Scientists, UN agencies, and indigenous and local communities agree that we have reached a critical time for biodiversity globally. But who will decide on the policies for protection of biodiversity? Triage may be on the agenda of pessimistic conservation scientists, but indigenous and local communities would rarely have such hubris as to assume that they have the wisdom to make triage decisions, and nor would many communities have the arrogance to think they have the right to intervene in this way in their complex ecosystems.

While debates continue and biodiversity declines annually, there is a group of actors who will be crucial in decisions on our planet's future, including biodiversity and climate change. The world's population is now predominantly urban [32]. It is urban citizens who are driving the exploitation of the world's ecosystems and the model of unsustainable over-consumption [33]. It is highly likely that it is urban populations who will decide the fate of biodiversity and climate change, through their decisions about resource use and consumption [34, 35].

We demand a great deal of urban populations when we ask them to lead a sustainable future. The majority of urban citizens are trained, as are most scientists, to hold a utilitarian view of the environment. Perhaps this is the great hubris of recent human history—the assumptions of the anthropocentric view of the global ecosystem: seeing our planet only for its services or its threats, and viewing ourselves as somehow external to the integrity of the ecosystem. And our most profound arrogance is in the assumption that we understand the implications of our destruction of biodiversity for the well-being of future generations.

There is much to be learnt from the indigenous and local communities who depend directly on, value spiritually, and fight for, their biodiverse ecosystems. And perhaps the most difficult thing to learn is the humility that these communities have—they do not assume that they know enough about the ecosystem to be able to decide which species the planet needs and which it does not. They do not hold a model that sees human beings as separate from their global ecosystem in all its complex biological and cultural diversity. They do not see themselves as owners of the planet, but as guardians of it for the future.

2012 will see a plethora of UN and government meetings devoted to the Rio  +20 summit and its theme of a green economy in the context of sustainable development and poverty eradication. Biodiversity and climate change should be key concerns of this meeting. But it will not be global summits that protect biodiversity or reduce the emissions that produce climate change—and it will not be scientists arguing for and against the utilitarian concept of ecosystem services. The real decision-makers will be every human on the planet and their resource needs and their choices. We have some evidence of what the global population 'needs', in terms of food, water and shelter [36], but we do not know for sure what they will 'choose'. More worryingly, even if the global population chooses to change their view of the planet and their place in it, and to reduce resource consumption to sustainable levels, we do not know if we will be in time.

ERL focus issue on biodiversity, human health and well-being

ERL is contributing to Rio  +  20 through a special issue devoted to the issues of biodiversity, human health and well-being. We particularly welcome papers from scientists and community groups working on biodiversity from the perspective of a broad understanding of health and well-being, including spiritual, cultural and intergenerational aspects; urban groups working on biodiversity and well-being; and the links of biodiversity to the green economy in the context of sustainable development and poverty alleviation.

References

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[2] Kinver M and Gill V 2011 Botanists discover 'remarkable' night-flowering orchid BBC News Science and Environment (www.bbc.co.uk/news/science-environment-15818662)

[3] Rudd M A 2011 Scientists' opinions on the global status and management of biological diversity Conserv. Biol.25 1165–75

[4] Bottrill M C et al 2008 Is conservation triage just smart decision making? Trends Ecol. Evol.23 649–54

[5] Parr M J et al 2009 Why we should aim for zero extinction Trends Ecol. Evol.24 181 Bottrill M C et al 2009 Finite conservation funds mean triage is unavoidable Trends Ecol. Evol.24 183–4

[6] Pushpangadan P and Behl H M 2005 Environment & Biodiversity: Agenda for Future (Lucknow: International Society of Environmental Botanists) (http://isebindia.com/icpep-3/icpep3-s-2.html)

[7] Alves R and Rosa I 2007 Biodiversity, traditional medicine and public health: where do they meet? J. Ethnobiol. Ethnomed.3 14

[8] Center for Biodiversity and Conservation 1997 Biodiversity and Human Health: A Guide for Policymakers (New York: American Museum of Natural History)

[9] Chivian E 1997 Global environmental degradation and biodiversity loss: implications for human health Biodiversity and Human Health ed F Grifo and J Rosenthal (Washington, DC: Island) pp 7–38

[10] UNEP-WCMC 2011 Health and Well Being of Communities Directly Dependent on Ecosystem Goods and Services: An Indicator for the Convention on Biological Diversity (Cambridge: UNEP-World Conservation Monitoring Centre)

[11] Nettleton C, Stephens C and Bristow F 2007 Utz Wachil: a study of indigenous perceptions of health and environment in five countries Ecohealth4 461–772

[12] Jones G P et al 2004 Coral decline threatens fish biodiversity in marine reserves Proc. Natl Acad. Sci.101 8251–3

[13] Merson J 2000 Bio-prospecting or bio-piracy: intellectual property rights and biodiversity in a colonial and postcolonial context Osiris15 282–96

[14] Soejarto D D 1996 Biodiversity prospecting and benefit-sharing: perspectives from the field J. Ethnopharmacol.51 1–15

[15] Foley J A et al 2007 Amazonia revealed: forest degradation and loss of ecosystem goods and services in the Amazon Basin Front. Ecol. Environ.5 25–32

[16] King S R, Carlson T J and Moran K 1996 Biological diversity, indigenous knowledge, drug discovery and intellectual property rights: creating reciprocity and maintaining relationships J. Ethnopharmacol.51 45–57

[17] Witzig R and Ascencios M 1999 The road to indigenous extinction: case study of resource exportation, disease importation, and human rights violations against the Urarina in the Peruvian Amazon Health Hum. Rights4 60–81

[18] Fundacion Proyungas 2007 Bitácora de las Yungas: Bosques Nublados (Tucuman: Fundacion de las Yungas)

[19] US Government 2003 Conserving Biodiversity in the Amazon Basin: Context and Opportunities for USAID (Washington, DC: USAID)

[20] Montenegro R A and Stephens C 2006 Indigenous health in Latin America and the Caribbean Lancet367 1859–69

[21] Stephens C, Nettleton C and Bristow F (ed) 2003 Utz' Wach'il: Health and Well-Being Among Indigenous Peoples (London: Health Unlimited and the London School of Hygiene and Tropical Medicine) (http://www.lshtm.ac.uk/php/sehr/indigenous/docs/utzpamphlet.pdf)

[22] Brown A et al 2007 Finca San Andres—Un Espacio de Cambios Ambientales y Sociales en el Alto Bermejo (Ediciones del Subtropico: Yerba Buena)

[23] Ramos A and Junqueira R 2010 The contribution of indigenous people to forest conservation and recovery Everything is Connected: Climate and Biodiversity in a Fragile World ed C Foley (London: DEFRA) (http://sd.defra.gov.uk/2010/11/everything-is-connected-climate-and-biodiversity-in-a-fragile-world/)

[24] Dunning E, Osti M and Pavese H 2010 The role of protected areas in mitigating climate change and conserving biodiversity Everything is Connected: Climate and Biodiversity in a Fragile World ed C Foley (London: DEFRA) pp 7–10 (http://sd.defra.gov.uk/2010/11/everything-is-connected-climate-and-biodiversity-in-a-fragile-world/)

[25] Kunst C R, Bravo S and Panagatti J L (ed) 2003 Fuego en los Ecosistemas Argentinos (Santiago del Estero: Instituto Nacional de Tecnología Agropecuaria)

[26] Miranda C P 2003 Tucumán y Los Recursos Naturales. Biodiversidad Los Recursos Silvestres, Los Ambientes Naturales y Las Areas Protegidas (Tucumán: Gobierno de La Provincia de Tucumán)

[27] Redford K H, Naughton L and Ráez-Luna E F 2000 Forest wildlife and its exploitation by humans The Conservation Atlas of Tropical Forests: The Americas ed C S Harcourt and J A Sayer (New York: Simon and Schuster/IUCN)

[28] Kappelle M and Brown A (ed) 2001 Bosques Nublados del Neotrópico (San Jose: Editorial INBio)

[29] Hall G and Patrinos H A 2005 Indigenous Peoples, Poverty and Human Development in Latin America: 1994–2004 (Washington, DC: The World Bank)

[30] Macchi M 2008 Indigenous and Traditional Peoples and Climate Change (Geneva: IUCN)

[31] IUCN 2011 IUCN to review and advance implementation of the 'new conservation paradigm' focusing on rights of indigenous peoples CEESP News, 2 May 2011 (available from: www.iucn.org/about/union/commissions/ceesp/ceesp news/?7399/IUCN-to-review-and-advance-implementation-of-the-new-conservation-paradigm, cited 29 November 2011)

[32] UN Habitat 2010 State of the World's Cities 2010/2011: Bridging the Urban Divide (Nairobi: UN Human Settlements Programme) (first published by Earthscan 2008)

[33] Rees W 1996 Ecological footprints of the future. Overview People Planet5 (2) 6–9

[34] Stephens C 2011 Revisting urban health and social inequalities: the devil is in the detail and the solution is in all of us Environ. Urban.23 29–40

[35] Anderson J M 2005 Blueprint for a greener city: growth need not cost the earth Water Sci. Technol.52 61–7

[36] United Nations Population Division 2008 World Urbanization Prospects: The 2007 Revision Population Database (New York: United Nations Population Division)

Myhrvold and Caldeira worked out the climate consequences of various ways in which the world's current fleet of coal power plants could evolve into something different [1]. They imagined one-fortieth of the world's coal plants being closed down each year for 40 years. Two limiting cases are (1) nothing is built to take the place of this power, because efficiency gains have made them unnecessary, and (2) coal plants exactly like those now running take their place. Since coal power is the most carbon-intensive form of power, all other options fall between these limits. They looked at six single-technology alternatives: taking over from coal as we know it are coal with carbon dioxide capture and storage, natural gas, nuclear power and three forms of intermittent renewables (presented as baseload options). Moreover, whatever the alternative, it remains in place unchanged from year 40 through year 100.

Results are presented as 100 yr trajectories for the increment in the average global surface temperature due only to this power production. For the coal-for-coal scenario, the surface temperature increase is about 0.13 °C in 40 yr and 0.31 °C in 100 yr. For the efficiency-for-coal scenario, the rise is 0.07 °C in 40 yr and 0.06 °C in 100 yr. Clearly, temperature rise is approximately proportional to emissions and these are self-consistent answers. For example, after 40 yr efficiency-for-coal has brought approximately half the temperature rise of coal-for-coal, and there have been exactly half the emissions. The efficiency-for-coal trajectory falls ever so slightly between years 40 and 100, because once CO₂ enters the atmosphere it lingers.

As for the absolute magnitude of the coal-to-coal trajectory, today's global coal power production (8300 TWh in 2008) is almost exactly what would be produced from one thousand one-gigawatt coal plants running flat out (8760 TWh), which is the coal power production assumed by Myhrvold and Caldeira. From table S1 of their paper, each GW-year of coal power production is accompanied by 6.59 Mt of CO₂ emissions. Thus, a century of this coal will emit 659 billion tons of CO₂. A rule of thumb recently promoted associates each trillion tons of carbon emissions (each 3.7 trillion tons of CO₂ emissions) with a long-term temperature rise whose fifth and 95th per cent confidence intervals are 1.0 and 2.1 °C [2]. With this rule of thumb, the long-term temperature rise should fall between 0.18 and 0.38 °C, so the estimated rise of 0.31 °C agrees with the rule of thumb.

Much of the paper is about estimates of the emissions for the alternatives to coal and efficiency. Emissions are estimated for building the physical stock as well as running it. The authors cite a high and a low value for each alternative, and the lower limits, with one exception, are close to what most analysis assumes. (The exception is natural gas, whose lower limit is 60% of the value for coal, even though values of 50% or lower are widely claimed.) The high limits are unorthodox and are already creating consternation. The high limit for hydropower reflects large emissions of methane from the lakes that form behind dams. In the cases of nuclear power, solar electric power, solar thermal power and wind power, the high limits can be attributed to emissions during construction. One suspects that these high values are straw men, avoidable with care.

It is illuminating to compare the Myhrvold–Caldeira partial emissions scenarios with the two full blown scenarios of the International Energy Agency (IEA)—the Current Policy Scenario and the 450 Scenario, presented in World Energy Outlook 2010 [3]. Both IEA scenarios go only to 2035. In the Current Policies Scenario, coal emissions approximately double by 2035 (to 16 500 TWh); Myhrvold and Caldeira actually do not tell us that this is where global coal power is heading, in the absence of new policies and priorities.

As for the IEA's 450 Scenario, it provides insight into the 40 yr phase-out for global coal power chosen by Myhrvold and Caldeira as their base case. In the 450 Scenario, global coal power falls to 5600 TWh in 2035, down one third from its 2008 value. By contrast, the pace for coal phase-out explored in the Myhrvold and Caldeira paper is about twice as fast: if their 40 yr phase-out had started in 2008, by 2035—27 yr later—global coal production would have fallen by about two thirds. I think one can view the 450 Scenario as capturing the IEA's judgment about the fastest achievable decarbonization of the world energy system. It is sobering to realize that allowing 40 yr for the closing out of world coal power production, which might strike some readers as relaxed, is actually so intense as to stretch credibility.

The IEA 450 Scenario also sheds light on the small fraction of the potential change in the future of the global energy system that the Myhrvold–Caldeira paper captures. The 2700 TWh reduction in coal power production between 2008 and 2035 in the 450 Scenario is smaller in magnitude than the increases in wind power (3900 TWh), nuclear power (3700 TWh), and hydropower (2800 TWh) in the same interval. Myhrvold and Caldeira present a textbook exercise, not to be confused with an exploration of the full range of possible futures.

I would not recommend this paper for its insight into energy systems. Rather, I would recommend it, strongly, as one of the rare papers that adequately confronts both of the sources of inertia that characterize our world: the inertia of the climate system epitomized by the durability of atmospheric CO₂ and the inertia of the energy system epitomized by the durability of our capital stock. Confronting this inertia can lead us to despair that what we can change for the better each year matters so little. Or it can inspire us, because what we do each year that points in the wrong direction will take so long to undo.

References

[1] Myhrvold N P and Caldeira K 2012 Greenhouse gases, climate change and the transition from coal to low-carbon electricity Environ. Res. Lett.7 014019

[2] Matthews H D, Gillett N P, Stott P A and Zickfeld K 2009 Nature459 829

[3] IEA 2010 World Energy Outlook 2010 (Paris: IEA)

A novel synergistic approach to reducing emissions from residential wood combustion (RWC) is presented. Wood energy fuel cycle optimization (FCO) aims to provide cleaner burning fuels through optimization of forestry and renewable energy management practices. In this work, beech and spruce forests of average and high quality were modelled and analysed to determine the volume of fuel wood and its associated bark fraction produced during typical forestry cycles. Two separate fuel wood bark production regimes were observed for beech trees, while only one production regime was observed for spruce. The single tree and stand models were combined with existing thinning parameters to replicate existing management practices. Utilizing estimates of initial seedling numbers and existing thinning patterns a dynamic model was formed that responded to changes in thinning practices. By varying the thinning parameters, this model enabled optimization of the forestry practices for the reduction of bark impurities in the fuel wood supply chain. Beech forestry cycles responded well to fuel cycle optimization with volume reductions of bark from fuel wood of between ∼10% and ∼20% for average and high quality forest stands. Spruce, on the other hand, was fairly insensitive to FCO with bark reductions of 0–5%. The responsiveness of beech to FCO further supports its status as the preferred RWC fuel in Switzerland. FCO could easily be extended beyond Switzerland and applied across continental Europe and North America.

This letter presents the contribution of black carbon (BC) to the total aerosol optical depth (AOD) and subsequently to the direct radiative forcing (DRF) at Manora Peak in the Indian Himalayan foothills. Measurements of the chemical composition of aerosols, carried out from July 2006 to May 2007, together with concurrently measured BC mass concentrations were used in an aerosol optical model to deduce the radiatively important aerosol optical parameters for composite aerosols. On the other hand, BC mass concentrations alone were used in the optical model to deduce the optical parameters solely for BC aerosols. The derived aerosol optical parameters were used independently in a radiative transfer model to estimate the DRF separately for composite and BC aerosols. The average BC mass concentration was found to be 0.98 (±0.68) μg m⁻³ during the entire observation period, which contributes <3% to the total aerosol mass and ∼17% to the total AOD at Manora Peak. The mean surface forcing was found to be  − 14.0 (±9.7) and  − 7.4 (±2.1) W m⁻², respectively for composite and BC aerosols whereas mean atmospheric forcing was about +14 (±10) and +10 (±3) W m⁻² for these aerosols. These results suggest that BC aerosols exert relatively large surface heating (∼45% higher) as compared to composite aerosols and contribute ∼70% to the total atmospheric forcing at Manora Peak. Such a large warming effect of BC may affect the strength of Himalayan glaciers, monsoon circulation and precipitation over the Indian region.

Eleven years (2000–10) of monthly observations from the National Aeronautics and Space Administration (NASA) Terra Moderate-resolution Imaging Spectroradiometer (MODIS) show the diurnal, seasonal, and inter-annual variations of skin temperature over the Tibetan plateau (75–100°E, 27–45°N) at 0.05° × 0.05° resolution. A slight warming trend is observed during this period of time, although the relatively short duration of the observation makes such a trend uncertain. More importantly, using the most recent climatology of land skin temperature, spatially high correlation coefficients are found among normalized difference vegetation index (NDVI), water vapor and cloud relations, indicating that the land surface, vegetation and atmosphere influence one another. Such a quantitative understanding of these relationships at high spatial resolution would be helpful for modeling the biosphere–atmosphere–land surface interaction processes over the Tibetan plateau.

The relationship between summer temperature, total cloud cover and precipitation over Eurasia was investigated using observation-based products of temperature and precipitation, and satellite-derived cloud cover and radiation products. We used a partial least squares regression approach to separate the local influences of cloud cover and precipitation on temperature variations. Our results suggest that the variance of summer temperature is partly explained by changes in summer cloudiness. The summer temperature dependence on cloud cover is strong at the high latitudes and in the middle latitude semi-humid area, while the dependence on precipitation is strong in the Central Asia arid area and the southern Asia humid area. During the period 1982–2009, the damped warming in extended West Siberia was accompanied with increases in cloud cover, and the pronounced warming in Europe and Mongolia was associated with a decrease in cloud cover and precipitation. Our results suggest that cloud cover may be the important local factor influencing the summer temperature variation in Eurasia while precipitation plays an important role at the middle latitudes.

The power generated by a wind turbine largely depends on the wind speed. During time periods with identical hub-height wind speeds but different shapes to the wind profile, a turbine will produce different amounts of power. This variability may be induced by atmospheric stability, which affects profiles of mean wind speed, direction and turbulence across the rotor disk. Our letter examines turbine power generation data, segregated by atmospheric stability, in order to investigate power performance dependences at a West Coast North American wind farm. The dependence of power on stability is clear, regardless of whether time periods are segregated by three-dimensional turbulence, turbulence intensity or wind shear. The power generated at a given wind speed is higher under stable conditions and lower under strongly convective conditions: average power output differences approach 15%. Wind energy resource assessment and day ahead power forecasting could benefit from increased accuracy if atmospheric stability impacts were measured and appropriately incorporated in power forecasts, e.g., through the generation of power curves based on a range of turbulence regimes.

Observed changes such as increasing global temperatures and the intensification of the global water cycle in the 20th century are robust results of coupled general circulation models (CGCMs). In spite of these successes, model-to-model variability and biases that are small in first order climate responses, however, have considerable implications for climate predictability especially when multi-model means are used. We show that most climate simulations of the 20th and 21st century A2 scenario performed with CMIP3 (Coupled Model Inter-comparison Project Phase 3) models have deficiencies in simulating the global atmospheric moisture balance. Large biases of only a few models (some biases reach the simulated global precipitation changes in the 20th and 21st centuries) affect the multi-model mean global moisture budget. An imbalanced flux of −0.14 Sv exists while the multi-model median imbalance is only −0.02 Sv. Moreover, for most models the detected imbalance changes over time. As a consequence, in 13 of the 18 CMIP3 models examined, global annual mean precipitation exceeds global evaporation, indicating that there should be a 'leaking' of moisture from the atmosphere whereas for the remaining five models a 'flooding' is implied. Nonetheless, in all models, the actual atmospheric moisture content and its variability correctly increases during the course of the 20th and 21st centuries. These discrepancies therefore imply an unphysical and hence 'ghost' sink/source of atmospheric moisture in the models whose atmospheres flood/leak. The ghost source/sink of moisture can also be regarded as atmospheric latent heating/cooling and hence as positive/negative perturbation of the atmospheric energy budget or non-radiative forcing in the range of −1 to +6 W m⁻² (median +0.1 W m⁻²). The inter-model variability of the global atmospheric moisture transport from oceans to land areas, which impacts the terrestrial water cycle, is also quite high and ranges from 0.26 to 1.78 Sv. In the 21st century this transport to land increases by about 5% per century with a model-to-model range from 1 to 13%. We suggest that this variability is weakly correlated to the land–sea contrast in air temperature change of these models. Spatially heterogeneous forcings such as aerosols contribute to the variability in moisture transport, at least in one model. The polewards shifts of dry zones in climate simulations of the 21st century are also assessed. It is shown that the multi-model means of the two subsets of models with negative and positive imbalances in the atmospheric moisture budget produce spatial variability in the dry zone positions similar in size to the spatial shifts expected from 21st century global warming. Thus, the selection of models also affects the multi-model mean dry zone extension. In general, we caution the use of multi-model means of E − P fields and suggest self-consistency tests for climate models.

The most up to date consensus from global climate models predicts warming in the Northern Hemisphere (NH) high latitudes to middle latitudes during boreal winter. However, recent trends in observed NH winter surface temperatures diverge from these projections. For the last two decades, large-scale cooling trends have existed instead across large stretches of eastern North America and northern Eurasia. We argue that this unforeseen trend is probably not due to internal variability alone. Instead, evidence suggests that summer and autumn warming trends are concurrent with increases in high-latitude moisture and an increase in Eurasian snow cover, which dynamically induces large-scale wintertime cooling. Understanding this counterintuitive response to radiative warming of the climate system has the potential for improving climate predictions at seasonal and longer timescales.

Blowing dust from agricultural fields has serious health and economic effects, which can be mitigated by soil conservation techniques. However, it is difficult to isolate improved land management in downstream records of airborne dust. In this letter we present multi-decadal (1961–2006) records of airborne dust frequency from seven weather stations across the Canadian Prairies. We related temporal changes in dust frequency to the climatic wind erosion potential and agricultural census data. We identified a statistically significant regime shift in the region-wide dust time series at 1990, with a substantial reduction in dust frequency thereafter. The correspondence between dust frequency and the climatic wind erosion potential improved from 1961–90 (r² = 0.154, p < 0.001) to 1991–2006 (r² = 0.429, p < 0.001). We interpret this as indicating that the climate signal was obscured by poor soil conservation practices in 1961–90, leading to dustier conditions. Post 1990, improved land management reduced the impact of land-use practices; only the most severe climate forcings resulted in detectable dust. The dramatic reduction of dust from 1990 onward appears to represent a region-wide threshold crossing, where the effects of soil conservation efforts began to materialize. Overall, the results suggest that soil conservation initiatives have had an impact in reducing airborne dust on the Canadian Prairies.

The majority of the world's food production capability is inextricably tied to global precipitation patterns. Changes in moisture availability—whether from changes in climate from anthropogenic greenhouse gas emissions or those induced by land cover change (LCC)—can have profound impacts on food production. In this study, we examined the patterns of evaporative sources that contribute to moisture availability over five major global food producing regions (breadbaskets), and the potential for land cover change to influence these moisture sources by altering surface evapotranspiration. For a range of LCC scenarios we estimated the impact of altered surface fluxes on crop moisture availability and potential yield using a simplified linear hydrologic model and a state-of-the-art ecosystem and crop model. All the breadbasket regions were found to be susceptible to reductions in moisture owing to perturbations in evaporative source (ES) from LCC, with reductions in moisture availability ranging from 7 to 17% leading to potential crop yield reductions of 1–17%, which are magnitudes comparable to the changes anticipated with greenhouse warming. The sensitivity of these reductions in potential crop yield to varying magnitudes of LCC was not consistent among regions. Two variables explained most of these differences: the first was the magnitude of the potential moisture availability change, with regions exhibiting greater reductions in moisture availability also tending to exhibit greater changes in potential yield; the second was the soil moisture within crop root zones. Regions with mean growing season soil moisture fractions of saturation >0.5 typically had reduced impacts on potential crop yield. Our results indicate the existence of LCC thresholds that have the capability to create moisture shortages adversely affecting crop yields in major food producing regions, which could lead to future food supply disruptions in the absence of increased irrigation or other forms of water management.

The Community Land Model version 4 (CLM4) is applied to explore the spatial–temporal patterns of spring (April–May) vegetation growth trends over the northern mid–high latitudes (NMH) (>25°N) between 1982 and 2004. During the spring season through the 23 yr period, both the satellite-derived and simulated normalized difference vegetation index (NDVI) anomalies show a statistically significant correlation and an overall greening trend within the study area. Consistently with the observed NDVI–temperature relation, the CLM4 NDVI shows a significant positive association with the spring temperature anomaly for the NMH, North America and Eurasia. Large study areas experience temperature discontinuity associated with contrasting NDVI trends. Before and after the turning point (TP) of the temperature trends, climatic variability plays a dominant role, while the other environmental factors exert minor effects on the NDVI tendencies. Simulated vegetation growth is broadly stimulated by the increasing atmospheric CO₂. Trends show that nitrogen deposition increases NDVI mostly in southeastern China, and decreases NDVI mainly in western Russia after the temperature TP. Furthermore, land use-induced NDVI trends vary roughly with the respective changes in land management practices (crop areas and forest coverage). Our results highlight how non-climatic factors mitigate or exacerbate the impact of temperature on spring vegetation growth, particularly across regions with intensive human activity.

The Energy Independence and Security Act of 2007 set an annual US national production goal of 39.7 billion l of cellulosic ethanol by 2020. This paper explores the possibility of meeting that target by growing and processing Miscanthus  ×  giganteus. We define and assess six production scenarios in which active cropland and/or Conservation Reserve Program land are used to grow to Miscanthus. The crop and biorefinery locations are chosen with consideration of economic, land-use, water management and greenhouse gas (GHG) emissions reduction objectives. Using lifecycle assessment, the net GHG footprint of each scenario is evaluated, providing insight into the climate costs and benefits associated with each scenario's objectives. Assuming that indirect land-use change is successfully minimized or mitigated, the results suggest two major drivers for overall GHG impact of cellulosic ethanol from Miscanthus: (a) net soil carbon sequestration or emissions during Miscanthus cultivation and (b) GHG offset credits for electricity exported by biorefineries to the grid. Without these factors, the GHG intensity of bioethanol from Miscanthus is calculated to be 11–13 g CO₂-equivalent per MJ of fuel, which is 80–90% lower than gasoline. Including soil carbon sequestration and the power-offset credit results in net GHG sequestration up to 26 g CO₂-equivalent per MJ of fuel.

The viability of global climate models for forecasting the Indian monsoon is explored. Evaluation and intercomparison of model skills are employed to assess the reliability of individual models and to guide model selection strategies. Two dominant and unique patterns of Indian monsoon climatology are trends in maximum temperature and periodicity in total rainfall observed after 30 yr averaging over India. An examination of seven models and their ensembles reveals that no single model or model selection strategy outperforms the rest. The single-best model for the periodicity of Indian monsoon rainfall is the only model that captures a low-frequency natural climate oscillator thought to dictate the periodicity. The trend in maximum temperature, which most models are thought to handle relatively better, is best captured through a multimodel average compared to individual models. The results suggest a need to carefully evaluate individual models and model combinations, in addition to physical drivers where possible, for regional projections from global climate models.

Observations worldwide are providing an increasing amount of atmosphere–ecosystem flux data. Thus, the establishment of a data mining methodology to detect significant trends and attribute changes to specific factors is important. This study examined the possibility of detecting significant trends in observed data at a test site with one of the longest records of flux measurements (Takayama, Japan). Statistical tests using non-parametric methods showed a 'likely' trend (i.e., detected at 66–90% confidence level) of increasing carbon sequestration. To investigate the change in carbon sequestration in relation to biological and environmental factors (ambient CO₂, temperature, radiation, precipitation and disturbance), mechanistic and numerical methods were applied. A process-based model was used for the mechanistic attribution of change, and an optimal fingerprinting method in combination with model-based sensitivity simulations was used for numerical attribution. At the study site, local disturbances appeared to exert an impact on the observed carbon sequestration, whereas climatic factors made moderate contributions. These results indicate the feasibility of detection and attribution using current flux measurement data, although more evidence is needed to confirm global coherence.

This letter proposes a new carbon labelling scheme to improve the visibility of products' life cycle carbon emissions (sometimes defined as carbon footprint). This approach starts by normalizing carbon emissions data on a common scale of 'carbon emissions intensity', and a new indicator 'carbon emissions intensity ratio' is generated based upon its ratio to the annual national greenhouse gas emission per gross domestic product. Five ranges (extremely low, low, medium, high and extremely high) are used to represent the level of carbon emissions intensity ratio by a simple diagram with colour gradation. Case examples are presented, in which the carbon emissions intensity ratios of various selected products, both distinct and related, are calculated and compared. The limitations of this approach are then discussed, laying a foundation for further work.

The Kyoto Protocol's Clean Development Mechanism (CDM) has experienced a rapid growth. Up to 2010, 2763 projects have been registered, standing for about 433 million ton CO₂ equivalent (CO₂-eq.) of annual carbon credits. However, the performances of CDM host countries are remarkably unbalanced. Previous literature suggested that economic and investment conditions, energy intensity, energy structure, the share of annual carbon credits from high global warming potential (GWP) green house gas (GHG), capacity and institutional buildings of domestic CDM governance can play important roles in promoting CDM. This quantitative analysis shows that domestic economic and investment conditions are the most decisive factors determining the performance of the CDM host countries. Additionally, the influence of carbon intensity of energy consumption is relatively modest, and energy intensity of GDP as well as the share of annual carbon credits from high GWP GHG is less significant. Moreover, several leading CDM countries are not as successful as they seem to be, when the influences of their vast territories, distinguished economic and investment conditions are excluded. Therefore, to simply transplant the CDM governances of these countries can hardly guarantee that other countries will boost their carbon credit outputs.

A number of options are available for adapting ecosystem management to improve resilience in the face of climatic changes. However, uncertainty exists as to the effectiveness of these options. A report prepared for the US Climate Change Science Program reviewed adaptation options for a range of federally managed systems in the United States. The report included a qualitative uncertainty analysis of conceptual approaches to adaptation derived from the review. The approaches included reducing anthropogenic stressors, protecting key ecosystem features, maintaining representation, replicating, restoring, identifying refugia and relocating organisms. The results showed that the expert teams had the greatest scientific confidence in adaptation options that reduce anthropogenic stresses. Confidence in other approaches was lower because of gaps in understanding of ecosystem function, climate change impacts on ecosystems, and management effectiveness. This letter discusses insights gained from the confidence exercise and proposes strategies for improving future assessments of confidence for management adaptations to climate change.

We present measurements of potential gradient (PG) with associated meteorological variables and cloud profiles for two examples of convective boundary layer processes. Aerosol acts as a tracer layer to show lofting of the convective boundary layer; the rising aerosol layer results in a decrease in PG. In foggy conditions, the PG is seen to increase during the fog and then reduce as the fog lifts, as expected.

The 2009 'Black Saturday' bushfires led to 172 civilian deaths, and were proclaimed as one of Australia's worst natural disasters. The Victorian Bushfires Royal Commission was set up in the wake of the fires to investigate the circumstances surrounding the death of each fatality. Here, results from an analysis undertaken for the Commission to examine the household preparedness policy 'Prepare, Stay and Defend, or Leave Early' ('Stay or Go'), plus an examination of the Commission's recommendations, are explored in the broader context of adaptation to bushfire. We find Victoria ill adapted to complex bushfire risk events like Black Saturday due to changing settlement patterns and the known vulnerabilities of populations living in fire prone areas, and increasingly in the future due to the influence of climate change extending fire seasons and their severity. We suggest that uncertainty needs to be better acknowledged and managed in fire risk situations, and that the responsibility for fire preparedness should be more justly distributed. We suggest that a transformation in adaptation is required to effectively manage complex bushfire risk events like Black Saturday, and provide four key ways in which transformation in bushfire preparedness could be achieved.

A transition from the global system of coal-based electricity generation to low-greenhouse-gas-emission energy technologies is required to mitigate climate change in the long term. The use of current infrastructure to build this new low-emission system necessitates additional emissions of greenhouse gases, and the coal-based infrastructure will continue to emit substantial amounts of greenhouse gases as it is phased out. Furthermore, ocean thermal inertia delays the climate benefits of emissions reductions. By constructing a quantitative model of energy system transitions that includes life-cycle emissions and the central physics of greenhouse warming, we estimate the global warming expected to occur as a result of build-outs of new energy technologies ranging from 100 GW_e to 10 TW_e in size and 1–100 yr in duration. We show that rapid deployment of low-emission energy systems can do little to diminish the climate impacts in the first half of this century. Conservation, wind, solar, nuclear power, and possibly carbon capture and storage appear to be able to achieve substantial climate benefits in the second half of this century; however, natural gas cannot.

A method for estimating the area of crop damage due to tropical cyclones (TCs) by using fragility curves (FCs) is proposed. FCs, which represent the probability of damage caused by external forces, are one method considered appropriate for estimating structural damage caused by natural disasters. Here, FCs are applied to estimate the area of damage to paddy rice resulting from typhoons in Japan. The FCs for paddy rice are assumed to vary with growth stage. Statistical data on areas damaged by 42 typhoons that have struck Japan between 1991 and 2007, together with observed meteorological data, are used to derive the FCs. In general, our estimates agree with the reported areas of damage for the 42 typhoons, especially for typhoons that affected large areas of paddy rice. Moreover, from statistical data on crop damage due to typhoons, the proposed method successfully shows that the heading stage of paddy rice is the stage most vulnerable to typhoons, as found in earlier experimental studies and post-disaster investigations.

Himalayan glaciers are a vital water source for people in the high regions of Asia. Their complete melting would be a crisis for approximately 1 billion people. Albedo is one of the key parameters that affect the energy balance of the snow and ice surfaces. Since 2000, albedos have been retrieved from satellite data for eleven representative Himalayan glaciers. It was found that most of the glaciers showed declining trends in the albedo of their upper areas, indicating that they have generally become darker in the past decade. A simulation case study in conjunction with in situ measurements showed that light-absorbing constituents (e.g., black carbon and dust) could be partly responsible for this phenomenon during late springtime; the background regional warming could also be responsible. The current surface radiation absorption in Himalayan glaciers could lead to significant melting, causing most of them to be in danger of rapid mass loss.

The post-depositional enrichment of black soot in snow-pack was investigated by measuring the redistribution of black soot along monthly snow-pits on a Tien Shan glacier. The one-year experiment revealed that black soot was greatly enriched, defined as the ratio of concentration to original snow concentration, in the unmelted snow-pack by at least an order of magnitude. Greatest soot enrichment was observed in the surface snow and the lower firn-pack within the melt season percolation zone. Black carbon (BC) concentrations as high as 400 ng g⁻¹ in the summer surface snow indicate that soot can significantly contribute to glacier melt. BC concentrations reaching 3000 ng g⁻¹ in the bottom portion of the firn pit are especially concerning given the expected equilibrium-line altitude (ELA) rise associated with future climatic warming, which would expose the dirty underlying firn and ice. Since most of the accumulation area on Tibetan glaciers is within the percolation zone where snow densification is characterized by melting and refreezing, the enrichment of black soot in the snow-pack is of foremost importance. Results suggest the effect of black soot on glacier melting may currently be underestimated.

A method for defining and classifying heatwave events in the Euro-Mediterranean region is presented. The definition is based on the 95th centile of the local temperature probability density function, with additional criteria for spatial and temporal extension. The heatwave events are then classified into six classes by cluster analysis. The six heatwave patterns of Europe are described and compared to the existing literature. The most catastrophic extreme heatwaves (e.g. 2003 in Europe, 2010 in Russia) are shown to belong to one of these classes. It is then shown that the different classes are associated with different physical mechanisms. The effect of synoptic circulation and hydrological conditions are notably investigated. In particular, a drought appears to be a pre-requisite to heatwave occurrence in some clusters but not all.

Regional climate models can successfully simulate tropical cyclones and typhoons. This has been shown and was evaluated for hindcast studies of the past few decades. But often global and regional weather phenomena are not simulated at the observed location, or occur too often or seldom even though the regional model is driven by global reanalysis data which constitute a near-realistic state of the global atmosphere. Therefore, several techniques have been developed in order to make the regional model follow the global state more closely. One is spectral nudging, which is applied for horizontal wind components with increasing strength for higher model levels in this study.

The aim of this study is to show the influence that this method has on the formation of tropical cyclones (TC) in regional climate models. Two ensemble simulations (each with five simulations) were computed for Southeast Asia and the Northwestern Pacific for the typhoon season 2004, one with spectral nudging and one without. First of all, spectral nudging reduced the overall TC number by about a factor of 2. But the number of tracks which are similar to observed best track data (BTD) was greatly increased. Also, spatial track density patterns were found to be more similar when using spectral nudging. The tracks merge after a short time for the spectral nudging simulations and then follow the BTD closely; for the no nudge cases the similarity is greatly reduced. A comparison of seasonal precipitation, geopotential height, and temperature fields at several height levels with observations and reanalysis data showed overall a smaller ensemble spread, higher pattern correlations and reduced root mean square errors and biases for the spectral nudged simulations. Vertical temperature profiles for selected TCs indicate that spectral nudging is not inhibiting TC development at higher levels. Both the Madden–Julian Oscillation and monsoonal precipitation are reproduced realistically by the regional model, with results slightly closer to reanalysis data for the spectral nudged simulations. On the basis of this regional climate model hindcast study of a single typhoon season, spectral nudging seems to be favourable since it has mostly positive effects on typhoon formation, location and general circulation patterns in the generation areas of TCs.

The agronomic use of charcoal from biomass pyrolysis (biochar) represents an interesting option for increasing soil fertility and sequestering atmospheric CO₂. However, before moving toward large-scale biochar applications, additional research must evaluate all possible land–atmosphere feedbacks. Despite the increasing number of studies investigating the effect of biochar on soil physical, chemical and biological properties, only a few have been done on surface albedo variations on agricultural lands. The present work had the aim of characterizing the annual albedo cycle for a durum wheat crop in Central Italy, by means of a spectroradiometer measurement campaign. Plots treated with biochar, at a rate of 30–60 t ha⁻¹, showed a surface albedo decrease of up to 80% (after the application) with respect to the control in bare soil conditions, while this difference tended to decrease during the crop growing season, because of the prevailing effect of canopy development on the radiometer response. After the post-harvesting tillage, the soil treated with biochar again showed a lower surface albedo value (<20–26% than the control), while the measurements taken in the second year after application suggested a clear decrease of biochar influence on soil color. The modeling of the surface energy balance highlighted changes in the partitioning of heat fluxes and in particular a substantial increase of ground heat fluxes on an annual basis.

We applied a land water mass balance equation over 59 major river basins during 2003–9 to estimate evapotranspiration (ET), using as input terrestrial water storage anomaly (TWSA) data from the GRACE satellites, precipitation and in situ runoff measurements. We found that the terrestrial water storage change cannot be neglected in the estimation of ET on an annual time step, especially in areas with relatively low ET values. We developed a spatial regression model of ET by integrating precipitation, temperature and satellite-derived normalized difference vegetation index (NDVI) data, and used this model to extrapolate the spatio-temporal patterns of changes in ET from 1982 to 2009. We found that the globally averaged land ET is about 604  mm yr⁻¹ with a range of 558–650  mm yr⁻¹. From 1982 to 2009, global land ET was found to increase at a rate of 1.10 mm yr⁻², with the Amazon regions and Southeast Asia showing the highest ET increasing trend. Further analyses, however, show that the increase in global land ET mainly occurred between the 1980s and the 1990s. The trend over the 2000s, its magnitude or even the sign of change substantially depended on the choice of the beginning year. This suggests a non-significant trend in global land ET over the last decade.

We tested the effects of ungulate grazing and nutrient availability on the temperature sensitivity of soil respiration (CO₂) and methane (CH₄) emissions in semi-natural temperate grassland. To do this, soil taken from long term grazed and ungrazed grassland was incubated at four temperatures (4, 10, 15 and 20 °C) with two levels of nutrient (NP) addition. The results showed that the variation in soil CO₂ and CH₄ emissions was explained by temperature and grazing, with grazing increasing the temperature sensitivity of CO₂ and CH₄ production by between 15 and 20 °C. This response was constrained by nutrient availability for CO₂, but not CH₄. These findings suggest that grazing could potentially have important impacts on the temperature sensitivity of greenhouse gas emissions in nutrient limited grasslands.

Global warming has the potential to negatively affect one of Canada's primary sources of winter recreation: hockey and ice skating on outdoor rinks. Observed changes in winter temperatures in Canada suggest changes in the meteorological conditions required to support the creation and maintenance of outdoor skating rinks; while there have been observed increases in the ice-free period of several natural water bodies, there has been no study of potential trends in the duration of the season supporting the construction of outdoor skating rinks. Here we show that the outdoor skating season (OSS) in Canada has significantly shortened in many regions of the country as a result of changing climate conditions. We first established a meteorological criterion for the beginning, and a proxy for the length of the OSS. We extracted this information from daily maximum temperature observations from 1951 to 2005, and tested it for significant changes over time due to global warming as well as due to changes in patterns of large-scale natural climate variability. We found that many locations have seen a statistically significant decrease in the OSS length, particularly in Southwest and Central Canada. This suggests that future global warming has the potential to significantly compromise the viability of outdoor skating in Canada.

High-albedo white and cool roofing membranes are recognized as a fundamental strategy that dense urban areas can deploy on a large scale, at low cost, to mitigate the urban heat island effect. We are monitoring three generic white membranes within New York City that represent a cross section of the dominant white membrane options for US flat roofs: (1) an ethylene–propylene–diene monomer (EPDM) rubber membrane; (2) a thermoplastic polyolefin (TPO) membrane; and (3) an asphaltic multi-ply built-up membrane coated with white elastomeric acrylic paint. The paint product is being used by New York City's government for the first major urban albedo enhancement program in its history. We report on the temperature and related albedo performance of these three membranes at three different sites over a multi-year period. The results indicate that the professionally installed white membranes are maintaining their temperature control effectively and are meeting the Energy Star Cool Roofing performance standards requiring a three-year aged albedo above 0.50. The EPDM membrane shows evidence of low emissivity; however this had the interesting effect of avoiding any 'winter heat penalty' for this building. The painted asphaltic surface shows high emissivity but lost about half of its initial albedo within two years of installation. Given that the acrylic approach is such an important 'do-it-yourself', low-cost, retrofit technique, and, as such, offers the most rapid technique for increasing urban albedo, further product performance research is recommended to identify conditions that optimize its long-term albedo control. Even so, its current multi-year performance still represents a significant albedo enhancement for urban heat island mitigation.

Researchers around the world are developing sustainable plant-based liquid transportation fuels (biofuels) to reduce petroleum consumption and greenhouse gas emissions. Algae are attractive because they promise large yields per acre compared to grasses, grains and trees, and because they produce oils that might be converted to diesel and gasoline equivalents. It takes considerable energy to produce algal biofuels with current technology; thus, the potential benefits of algal biofuels compared to petroleum fuels must be quantified. To this end, we identified key parameters for algal biofuel production using GREET, a tool for the life-cycle analysis of energy use and emissions in transportation systems. The baseline scenario produced 55 400 g CO₂ equivalent per million BTU of biodiesel compared to 101 000 g for low-sulfur petroleum diesel. The analysis considered the potential for greenhouse gas emissions from anaerobic digestion processes commonly used in algal biofuel models. The work also studied alternative scenarios, e.g., catalytic hydrothermal gasification, that may reduce these emissions. The analysis of the nitrogen recovery step from lipid-extracted algae (residues) highlighted the importance of considering the fate of the unrecovered nitrogen fraction, especially that which produces N₂O, a potent greenhouse gas with global warming potential 298 times that of CO₂.

Estimating emissions from deforestation and degradation of forests in many developing countries is so uncertain that the effects of changes in forest management could remain within error ranges (i.e. undetectable) for several years. Meanwhile UNFCCC Parties need consistent time series of meaningful performance indicators to set credible benchmarks and allocate REDD+ incentives to the countries, programs and activities that actually reduce emissions, while providing social and environmental benefits. Introducing widespread measuring of carbon in forest land (which would be required to estimate more accurately changes in emissions from degradation and forest management) will take time and considerable resources. To ensure the overall credibility and effectiveness of REDD+, parties must consider the design of cost-effective systems which can provide reliable and comparable data on anthropogenic forest emissions. Remote sensing can provide consistent time series of land cover maps for most non-Annex-I countries, retrospectively. These maps can be analyzed to identify the forests that are intact (i.e. beyond significant human influence), and whose fragmentation could be a proxy for degradation. This binary stratification of forests biomes (intact/non-intact), a transition matrix and the use of default carbon stock change factors can then be used to provide initial estimates of trends in emission changes. A proof-of-concept is provided for one biome of the Democratic Republic of the Congo over a virtual commitment period (2005–2010). This approach could allow assessment of the performance of the five REDD+ activities (deforestation, degradation, conservation, management and enhancement of forest carbon stocks) in a spatially explicit, verifiable manner. Incentives could then be tailored to prioritize activities depending on the national context and objectives.

Sound policies for protecting coastal communities and assets require good information about vulnerability to flooding. Here, we investigate the influence of sea level rise on expected storm surge-driven water levels and their frequencies along the contiguous United States. We use model output for global temperature changes, a semi-empirical model of global sea level rise, and long-term records from 55 nationally distributed tidal gauges to develop sea level rise projections at each gauge location. We employ more detailed records over the period 1979–2008 from the same gauges to elicit historic patterns of extreme high water events, and combine these statistics with anticipated relative sea level rise to project changing local extremes through 2050. We find that substantial changes in the frequency of what are now considered extreme water levels may occur even at locations with relatively slow local sea level rise, when the difference in height between presently common and rare water levels is small. We estimate that, by mid-century, some locations may experience high water levels annually that would qualify today as 'century' (i.e., having a chance of occurrence of 1% annually) extremes. Today's century levels become 'decade' (having a chance of 10% annually) or more frequent events at about a third of the study gauges, and the majority of locations see substantially higher frequency of previously rare storm-driven water heights in the future. These results add support to the need for policy approaches that consider the non-stationarity of extreme events when evaluating risks of adverse climate impacts.

Because sea level could rise 1 m or more during the next century, it is important to understand what land, communities and assets may be most at risk from increased flooding and eventual submersion. Employing a recent high-resolution edition of the National Elevation Dataset and using VDatum, a newly available tidal model covering the contiguous US, together with data from the 2010 Census, we quantify low-lying coastal land, housing and population relative to local mean high tide levels, which range from ∼0 to 3 m in elevation (North American Vertical Datum of 1988). Previous work at regional to national scales has sometimes equated elevation with the amount of sea level rise, leading to underestimated risk anywhere where the mean high tide elevation exceeds 0 m, and compromising comparisons across regions with different tidal levels. Using our tidally adjusted approach, we estimate the contiguous US population living on land within 1 m of high tide to be 3.7 million. In 544 municipalities and 38 counties, we find that over 10% of the population lives below this line; all told, some 2150 towns and cities have some degree of exposure. At the state level, Florida, Louisiana, California, New York and New Jersey have the largest sub-meter populations. We assess topographic susceptibility of land, housing and population to sea level rise for all coastal states, counties and municipalities, from 0 to 6 m above mean high tide, and find important threat levels for widely distributed communities of every size. We estimate that over 22.9 million Americans live on land within 6 m of local mean high tide.

The depth of the 2006–9 drought in the humid, southeastern US left several metropolitan areas with only a 60–120 day water supply. To put the region's recent drought variability in a long-term perspective, a dense and diverse tree-ring network—including the first records throughout the Apalachicola–Chattahoochee–Flint river basin—is used to reconstruct drought from 1665 to 2010 CE. The network accounts for up to 58.1% of the annual variance in warm-season drought during the 20th century and captures wet eras during the middle to late 20th century. The reconstruction shows that the recent droughts are not unprecedented over the last 346 years. Indeed, droughts of extended duration occurred more frequently between 1696 and 1820. Our results indicate that the era in which local and state water supply decisions were developed and the period of instrumental data upon which it is based are amongst the wettest since at least 1665. Given continued growth and subsequent industrial, agricultural and metropolitan demand throughout the southeast, insights from paleohydroclimate records suggest that the threat of water-related conflict in the region has potential to grow more intense in the decades to come.

China is the world's largest emitter of greenhouse gases (GHGs) and the agricultural sector in China is responsible for 17–20% of annual emissions and 62% of total freshwater use. Groundwater abstraction in China has increased rapidly from 10 km³ yr⁻¹ in the 1950s to more than 100 km³ yr⁻¹ in the 2000s, such that roughly 70% of the irrigated area in northern China is now groundwater-fed. Pumping of water for irrigation is one of the most energy consuming on-farm processes; however, to date this source of GHG emissions in China and elsewhere has been relatively neglected. We derive the first detailed estimate of GHG emissions from groundwater pumping for irrigation in China, using extensive village survey data from 11 provinces, broadly representative of the situation during the mid-2000s. The 11 provinces cover roughly half of China's irrigated cropland and we upscale to the national level using government statistics for the remaining 20 provinces. Our results show emissions of 33.1 MtCO₂e, just over half a per cent of the national total. Groundwater abstraction represents an important source of GHG emissions that has been rapidly increasing and which at present is largely unregulated. Water scarcity in China is already driving policies to improve water conservation. These results suggest that significant potential exists to promote the co-benefits of water and energy saving in order to meet national planning targets.

Glaciers in Southern Chile (39–43°S) are characterized by frontal retreats and area losses in response to the ongoing climatic changes at a timescale of decades. Superimposed on these longer-term trends, volcanic activity is thought to impact glaciers in variable ways. Debris–ash covered Glaciar Pichillancahue-Turbio only retreated slightly in recent decades in spite of been located on Volcán Villarrica which has experienced increased volcanic activity since 1977. In contrast, the negative long-term Volcán Michinmahuida glacier area trend reversed shortly before the beginning of the explosive eruption of nearby Volcán Chaitén in May 2008, when Glaciar Amarillo advanced and a lahar type of mudflow was observed. This advancing process is analysed in connection to the nearby eruption, producing albedo changes at Michinmahuida glaciers, as well as a possible enhanced basal melting from higher geothermal flux. Deconvolution of glacier responses due to these processes is difficult and probably not possible with available data. Much more work and data are required to determine the causes of present glacier behaviour.

To assess the impact of climate change on freshwater resources, change in mean annual runoff (MAR) is only a first indicator. In addition, it is necessary to analyze changes of river flow regimes, i.e. changes in the temporal dynamics of river discharge, as these are important for the well-being of humans (e.g. with respect to water supply) and freshwater-dependent biota (e.g. with respect to habitat availability). Therefore, we investigated, in a global-scale hydrological modeling study, the relation between climate-induced changes of MAR and changes of a number of river flow regime indicators, including mean river discharge, statistical low and high flows, and mean seasonal discharge. In addition, we identified, for the first time at the global scale, where flow regime shifts from perennial to intermittent flow regimes (or vice versa) may occur due to climate change. Climate-induced changes of all considered river flow regime indicators (except seasonal river flow changes) broadly follow the spatial pattern of MAR changes. The differences among the computed changes of MAR due to the application of the two climate models are larger than the differences between the change of MAR and the change of the diverse river flow indicators for one climate model. At the sub-basin and grid cell scales, however, there are significant differences between the changes of MAR, mean annual river discharge, and low and high flows. Low flows are projected to be more than halved by the 2050s in almost twice the area as compared to MAR. Similarly, northern hemisphere summer flows decrease more strongly than MAR. Differences between the high emissions scenario A2 (with emissions of 25 Gt C yr⁻¹ in the 2050s) and the low emissions scenario B2 (16 Gt C yr⁻¹) are generally small as compared to the differences due to the two climate models. The benefits of avoided emissions are, however, significant in those areas where flows are projected to be more than halved due to climate change. If emissions were constrained to the B2 scenario, the area with ecologically relevant flow regime shifts would be reduced to 5.4%–6.7% of the global land area as compared to 6.3%–7.0% in A2. In particular, under the B2 scenario, fewer rivers will change from perennial to intermittent (or transitional) river flows.

There is compelling evidence that glaciers are retreating in many mountainous areas of the world due to global warming. With this glacier retreat, new habitats are being exposed that are colonized by microorganisms whose diversity and function are less well studied. Here, we characterized bacterial diversity along the chronosequences of the glacier No. 1 foreland that follows glacier retreat. An average of 10 000 sequences was obtained from each sample by 454 pyrosequencing. Using non-parametric and rarefaction estimated analysis, we found bacterial phylotype richness was high. The bacterial species turnover rate was especially high between sites exposed for 6 and 10 yr. Pyrosequencing showed tremendous bacterial diversity, among which the Acidobacteria, Actinobacteria, Bacteroidetes and Proteobacteria were found to be present at larger numbers at the study area. Meanwhile, the proportion of Bacteroidetes and Proteobacteria decreased and the proportion of Acidobacteria increased along the chronosequences. Some known functional bacterial genera were also detected and the sulfur- and sulfate-reducing bacteria were present in a lower proportion of sequences. These findings suggest that high-throughput pyrosequencing can comprehensively detect bacteria in the foreland, including rare groups, and give a deeper understanding of the bacterial community structure and variation along the chronosequences.

In the Copenhagen Accord, nations agreed on the need to limit global warming to two degrees to avoid potentially dangerous climate change, while in policy circles negotiations have placed a particular emphasis on emissions in years 2020 and 2050. We investigate the link between the probability of global warming remaining below two degrees (above pre-industrial levels) right through to year 2500 and what this implies for emissions in years 2020 and 2050, and any long-term emissions floor. This is achieved by mapping out the consequences of alternative emissions trajectories, all in a probabilistic framework and with results placed in a simple-to-use set of graphics.

The options available for carbon dioxide-equivalent (CO₂e) emissions in years 2020 and 2050 are narrow if society wishes to stay, with a chance of more likely than not, below the 2 °C target. Since cumulative emissions of long-lived greenhouse gases, and particularly CO₂, are a key determinant of peak warming, the consequence of being near the top of emissions in the allowable range for 2020 is reduced flexibility in emissions in 2050 and higher required rates of societal decarbonization. Alternatively, higher 2020 emissions can be considered as reducing the probability of limiting warming to 2 °C. We find that the level of the long-term emissions floor has a strong influence on allowed 2020 and 2050 emissions for two degrees of global warming at a given probability. We place our analysis in the context of emissions pledges for year 2020 made at the end of and since the 2009 COP15 negotiations in Copenhagen.

This review paper summarizes current understanding of the transport of organic carbon to, and the fate of organic carbon within, the East Siberian Arctic Shelf (ESAS), and of processes determining carbon dioxide (CO₂) and methane (CH₄) fluxes from the ESAS to the atmosphere achieved from analyzing the data sets obtained on 20 expeditions performed from 1999 to 2011. This study of the ESAS was aimed at investigating how redistribution of old carbon from degrading terrestrial and sub-sea permafrost and from coastal erosion contributes to the carbon pool of the ESAS, how changes in the hydrological cycle of the surrounding land and alteration of terrestrial carbon cycles affect the hydrological and biogeochemical parameters of shelf water masses, and which factors control CH₄ and CO₂ emissions from the ESAS. This report describes selected results achieved by a developing international scientific partnership that has been crucial at every stage of the study and will be even more important in the future.

Stressors including regional climate change, economic development effects upon land use and an increasing demand for food production have resulted in significant impacts on the dryland ecosystems in the East Asia (DEA) region. Ecosystem services, such as its provisional services in providing forage for grazing as well as its functional services in regulating water and carbon fluxes, have been significantly altered over the past three decades. Conversely, changes in the landscape, particularly land cover types, have also been blamed for intensified climatic events such as dust storms and severe and frequent droughts within the region. The interactive nature of climate, ecosystems and society is complex and not fully understood, making it difficult, if not impossible, to develop effective adaptation strategies for the region. A special synthesis workshop on 'Dryland Ecosystems in East Asia: State, Changes, Knowledge Gaps, and Future' was held from 18–20 July 2011 in Kaifeng, Henan Province, China, with the aim of identifying knowledge gaps, quantifying impacts and developing a future research agenda for the region. The specific objectives of this workshop were to answer some key socio-environmental questions, including the following. (1) What do we know about the drylands in DEA? (2) What are the knowledge gaps? (3) What are the solutions to these issues? This paper provides a synthesis of the workshop consensus and findings on the state of knowledge and challenges in addressing these science issues for the DEA region.

An overview of the current status of the operational seasonal climate prediction for North Eurasia is presented. It is shown that the performance of existing climate models is rather poor in seasonal prediction for North Eurasia. Multi-model ensemble forecasts are more reliable than single-model ones; however, for North Eurasia they tend to be close to climatological ones. Application of downscaling methods may improve predictions for some locations (or regions). However, general improvement of the reliability of seasonal forecasts for North Eurasia requires improvement of the climate prediction models.

The discovery of oiled and non-oiled honeycomb material in the Gulf of Mexico surface waters and along coastal beaches shortly after the explosion of Deepwater Horizon sparked debate about its origin and the oil covering it. We show that the unknown pieces of oiled and non-oiled honeycomb material collected in the Gulf of Mexico were pieces of the riser pipe buoyancy module of Deepwater Horizon. Biomarker ratios confirmed that the oil had originated from the Macondo oil well and had undergone significant weathering. Using the National Oceanic and Atmospheric Administration's records of the oil spill trajectory at the sea surface, we show that the honeycomb material preceded the front edge of the uncertainty of the oil slick trajectory by several kilometers. We conclude that the observation of debris fields deriving from damaged marine materials may be incorporated into emergency response efforts and forecasting of coastal impacts during future offshore oil spills, and ground truthing predicative models.

Recent densification of shrub cover is now documented in many Arctic regions. However, most studies focus on global scale responses, yielding very little information on the local patterns. This research aims to quantify shrub cover increase at northern treeline (Québec, Canada) in two important types of environment, sandy terraces and hilltops (which cover about 70% of the landscape), and to identify the species involved. The comparison of a mosaic of two aerial photographs from 1957 (137 km²) and one satellite image taken in 2008 (151 km²) revealed that both hilltops and terraces recorded an increase in shrub cover. However, the increase was significantly greater on terraces than on hilltops (21.6% versus 11.6%). According to ground truthing, the shrub cover densification is associated mainly with an increase of Betula glandulosa Michx. The numerous seedlings observed during the ground truthing suggest that shrub densification should continue in the future.

Recent observations suggest that while some arctic landscapes are undergoing rapid change, others are apparently more resilient. In this study, we related surface cover and energy balance to microtopography in a degraded polygonal peat plateau (baydjarakh field) near Churchill, Manitoba in mid-summer 2010. The landscape consists of remnant high-centered polygons divided by troughs of varying widths. Historical aerial photos indicate these topographical features have been stable for over 80 years. Our goal was to explore patterns that might explain the apparent stability of this landscape over this time period and to evaluate remote sensing methods for characterizing microtopographic patterns that might resist change in the face of climate warming. Summertime surface albedo measurements were combined with several years of winter snow depth, snow heat flux, summer thaw depth and annual surface temperature, all of which had striking contrasts between wet troughs and high polygon centers. Measurements of albedo and the snowpack heat transfer coefficient were lowest for wet troughs (areas of standing water) dominated by graminoids, and were significantly higher for high polygon centers, dominated by dwarf shrubs and lichens. Snow depth, surface temperature and thaw depth were all significantly higher for wet troughs than high polygon centers. Together these patterns of cover and energy balance associated with microtopographic variation can contribute to the stability of this landscape through differential heat transfer and storage. We hypothesize that local thermal feedback effects, involving greater heat trapping in the troughs than on the baydjarakh tops, and effective insulation on the baydjarakh edges, have ensured landscape stability over most of the past century. These results suggest that high-resolution remote sensing, combined with detailed field monitoring, could provide insights into the dynamics or stability of arctic landscapes, where cover often varies over short distances due to microtopographic effects.

There is a growing body of empirical evidence documenting the expansion of shrub vegetation in the circumpolar Arctic in response to climate change. Here, we conduct a series of idealized experiments with the Community Climate System Model to analyze the potential impact on boreal climate of a large-scale tundra-to-shrub conversion. The model responds to an increase in shrub abundance with substantial atmospheric heating arising from two seasonal land–atmosphere feedbacks: a decrease in surface albedo and an evapotranspiration-induced increase in atmospheric moisture content. We demonstrate that the strength and timing of these feedbacks are sensitive to shrub height and the time at which branches and leaves protrude above the snow. Taller and aerodynamically rougher shrubs lower the albedo earlier in the spring and transpire more efficiently than shorter shrubs. These mechanisms increase, in turn, the strength of the indirect sea-ice albedo and ocean evaporation feedbacks contributing to additional regional warming. Finally, we find that an invasion of tall shrubs tends to systematically warm the soil, deepen the active layer, and destabilize the permafrost (with increased formation of taliks under a future scenario) more substantially than an invasion of short shrubs.

Satellite-based measurements of the normalized difference vegetation index (NDVI; an index of vegetation greenness and photosynthetic capacity) indicate that tundra environments are generally greening and becoming more productive as climates warm in the Arctic. The greening, however, varies and is even negative in some parts of the Arctic. To help interpret the space-based observations, the International Polar Year (IPY) Greening of the Arctic project conducted ground-based surveys along two >1500 km transects that span all five Arctic bioclimate subzones. Here we summarize the climate, soil, vegetation, biomass, and spectral information collected from the North America Arctic transect (NAAT), which has a more continental climate, and the Eurasia Arctic transect (EAT), which has a more oceanic climate. The transects have broadly similar summer temperature regimes and overall vegetation physiognomy, but strong differences in precipitation, especially winter precipitation, soil texture and pH, disturbance regimes, and plant species composition and structure. The results indicate that summer warmth and NDVI increased more strongly along the more continental transect.

Trees at Alaskan treelines are assumed to be limited by temperature and to expand upslope and/or to higher latitudes with global warming. However, recent studies describe negative temperature responses and drought stress of Alaskan treeline trees in recent decades. In this study, we have analyzed the responses of treeline white spruce to temperature and precipitation according to different climatic regimes in Alaska, described as negative (cool) and positive (warm) phases of the Pacific Decadal Oscillation (PDO). We found that in three consecutive phases (positive from 1925–46, negative from 1947–76, and positive again from 1977–98), the growth responses to temperature and precipitation differed markedly. Before 1947, in a phase of warm winters and with summer temperatures being close to the century mean, the trees at most sites responded positively to summer temperature, as one would expect from treeline trees at northern high latitudes. Between 1947 and 1976, a phase of cold winters and average summers, the trees showed similar responses, but a new pattern of negative responses to the summer temperature of the year prior to growth coupled with positive responses to the precipitation in the same year emerged at some sites. As the precipitation was relatively low at those sites, we assume that drought stress might have played a role. However, the climate responses were not uniform but were modified by regional gradients (trees at northern sites responded more often to temperature than trees at southern sites) and local site conditions (forest trees responded more often to precipitation than treeline trees), possibly reflecting differences in energy and water balance across regions and sites, respectively. However, since the shift in the PDO in 1976 from a negative to a positive phase, the trees' climate–growth responses are much less pronounced and climate seems to have lost its importance as a limiting factor for the growth of treeline white spruce. If predictions of continued warming and precipitation increase at northern high latitudes hold true, the growth of Alaskan treeline trees will likely depend on the ratio of temperature and precipitation increase more than on their absolute values, as well as on the interaction of periodic regime shifts with the global warming trend. Once a climatic limitation is lifted, other factors, such as insect outbreaks or interspecific competition, might become limiting to tree growth.

Numerous studies have evaluated the dynamics of Arctic tundra vegetation throughout the past few decades, using remotely sensed proxies of vegetation, such as the normalized difference vegetation index (NDVI). While extremely useful, these coarse-scale satellite-derived measurements give us minimal information with regard to how these changes are being expressed on the ground, in terms of tundra structure and function. In this analysis, we used a strong regression model between NDVI and aboveground tundra phytomass, developed from extensive field-harvested measurements of vegetation biomass, to estimate the biomass dynamics of the circumpolar Arctic tundra over the period of continuous satellite records (1982–2010). We found that the southernmost tundra subzones (C–E) dominate the increases in biomass, ranging from 20 to 26%, although there was a high degree of heterogeneity across regions, floristic provinces, and vegetation types. The estimated increase in carbon of the aboveground live vegetation of 0.40 Pg C over the past three decades is substantial, although quite small relative to anthropogenic C emissions. However, a 19.8% average increase in aboveground biomass has major implications for nearly all aspects of tundra ecosystems including hydrology, active layer depths, permafrost regimes, wildlife and human use of Arctic landscapes. While spatially extensive on-the-ground measurements of tundra biomass were conducted in the development of this analysis, validation is still impossible without more repeated, long-term monitoring of Arctic tundra biomass in the field.

How the greening of Arctic landscapes manifests as a change in ecosystem structure and function remains largely unknown. This study investigates the likely implications of plant community change on ecosystem function in tundra near Barrow, Alaska. We use structural data from marked plots, established in 1972 and resampled in 1999, 2008 and 2010 to assess plant community change. Ecosystem functional studies were made close to peak growing season in 2008 and 2010 on destructive plots adjacent to marked plots and included measurement of land–atmosphere CH₄ and CO₂ exchange, hyperspectral reflectance, albedo, water table height, soil moisture, and plant species cover and abundance. Species cover and abundance data from marked and destructive plots were analyzed together using non-metric multi-dimensional scaling (NMS) ordination. NMS axis scores from destructive plots were used to krig ecosystem function variables in ordination space and produce surface plots from which time series of functional attributes for resampled plots were derived. Generally, the greatest functional change was found in aquatic and wet plant communities, where productivity varied and soil moisture increased, increasing methane efflux. Functional change was minimal in moist and dry communities, which experienced a general decrease in soil moisture availability and appeared overall to be functionally more stable through time. Findings suggest that the Barrow landscape could have become less productive and less responsive to change and disturbance over the past few decades. This study is a contribution to the International Polar Year-Back to the Future Project (512).

Knowledge of how arctic plant communities will respond to change has been largely derived from plot level experimental manipulation, not from trends of decade time scale environmental observations. This study documents plant community change in 330 marked plots at 33 sites established during the International Biological Program near Barrow, Alaska in 1972. Plots were resampled in 1999, 2008 and 2010 for species cover and presence. Cluster analysis identified nine plant communities in 1972. Non-metric multidimensional scaling (NMS) indicates that plant communities have changed in different ways over time, and that wet communities have changed more than dry communities. The relative cover of lichens increased over time, while the response of other plant functional groups varied. Species richness and diversity also increased over time. The most dramatic changes in the cover of bryophytes, graminoids and bare ground coincided with a lemming high in 2008.

This letter reviews the scientific literature on whether and how environmental changes affect the risk of violent conflict. The available evidence from qualitative case studies indicates that environmental stress can contribute to violent conflict in some specific cases. Results from quantitative large-N studies, however, strongly suggest that we should be careful in drawing general conclusions. Those large-N studies that we regard as the most sophisticated ones obtain results that are not robust to alternative model specifications and, thus, have been debated. This suggests that environmental changes may, under specific circumstances, increase the risk of violent conflict, but not necessarily in a systematic way and unconditionally. Hence there is, to date, no scientific consensus on the impact of environmental changes on violent conflict. This letter also highlights the most important challenges for further research on the subject. One of the key issues is that the effects of environmental changes on violent conflict are likely to be contingent on a set of economic and political conditions that determine adaptation capacity. In the authors' view, the most important indirect effects are likely to lead from environmental changes via economic performance and migration to violent conflict.

Environmental factors, such as the frequency, intensity and duration of extreme weather events, are important drivers of migration and displacement of people. There is therefore a growing need for regional climate predictions for the coming seasons to decades. This paper reviews the current state of the art of seasonal to decadal climate prediction, focusing on the potential sources of skill, forecasting techniques, current capability and future prospects.

This letter probes the causal links between migration, remittances and resilience to environmental change. Three case studies have been chosen, Western Mexico, the Central Plateau of Burkina Faso and Eastern India, where satellite imagery shows recent regeneration of vegetative cover and where there is evidence of high rates of migration. The findings are analysed through a framework that draws on concepts of ecological anthropology, new economics of labour theories and livelihood analyses of migration drivers and impacts.

This article reviews the channels through which sea level rise can affect economic growth, namely the loss of land, the loss of infrastructure and physical capital, the loss of social capital, the additional cost from extreme events and coastal floods, and the increased expenditure for coastal protection. It discusses how existing studies on the direct impact of sea level rise could be used to investigate the resulting consequences on economic growth, emphasizes research needs on this question, and discusses consequences on migration.

Many countries in the more developed world, and some in the less developed, are facing new economic and social pressures associated with the ageing of their populations. Europe, in particular, is forecast to have a demographic deficit, which may be alleviated by in-migration to the region. However, several commentators have proposed that Europe will not be able to successfully compete with other regions, in particular Asia, in the coming years for the skills it will require. This letter explores these themes, arguing that climate change will increase the attractiveness of Europe as a destination of economic choice for future skilled workers, to the detriment of more environmentally challenged regions.

We omitted an acknowledgment of funding in our letter. It should read: Acknowledgments This research was funded by the National Oceanic and Atmospheric Administration Center for Sponsored Coastal Ocean Research under contract number NA09NOS4780208. This article is contribution No.3188 of the Virginia Institute of Marine Science.

The acknowledgment should additionally state: 'We would like to thank Drs Caroline Taylor and Heather Youngs from the Energy Biosciences Institute for their help in this research.'