Development of ambitious and realistic targets to reduce short-lived climate pollutant emissions in nationally determined contributions: case study for Colombia

Limiting global temperature increases to below 1.5 °C requires reductions in Short-Lived Climate Pollutants (SLCPs), like methane, black carbon, and hydrofluorocarbons (HFCs), which is rarely reflected in targets within Nationally Determined Contributions (NDCs). Colombia’s 2020 NDC is explored as a case study for how Governments can integrate SLCP mitigation targets into climate change commitments. Methane and HFC mitigation contribute approximately 9% of Colombia’s GHG reduction commitment, and a separate target is included to reduce black carbon emissions by 40% by 2030 compared to 2014 levels. These targets are shown to be ambitious, due to the inclusion of a new black carbon target, realistic due to the identification of mitigation measures to achieve them, and additional to CO2 mitigation. Analysis of the planning process establishing these targets emphasises the importance of long-term planning to obtain agreement between coordinating institutions and implementing institutions on the utility of SLCP targets, and capacity-building within national institutions.


Introduction
Short-Lived Climate Pollutants (SLCPs), including black carbon (BC), methane (CH 4 ), tropospheric ozone (O 3 ) and hydrofluorocarbons (HFCs) have, compared to carbon dioxide (CO 2 ), relatively short atmospheric lifetimes (days to ∼15 years) (UNEP/WMO 2011).They contribute to global temperature increases (IPCC 2021), and air pollution's large health burden (Cohen et al 2017, Malley et al 2017).Mitigation of SLCPs is necessary to achieve the Paris Agreement's goal to keep global temperature increases 'well below 2 °C', and ideally to 1.5 °C (IPCC 2018).The extent of the climate change and air quality benefits from SLCP mitigation depends on the specific mitigation measures that are implemented that target major SLCP sources.For example, methane and HFC emission reductions will always result in a net cooling (UNEP CCAC 2021).For black carbon, its main sources (household solid fuel use, diesel transport, biomass burning, waste burning) also emit other pollutants with both positive and negative radiative forcings (Bond et al 2013).The ratio of black carbon to other pollutant emissions for a source, and the extent to which mitigation reduces black carbon and other pollutants, determines the overall climate and air quality impact from targeting major black carbon sources (Aamaas et al 2017, Harmsen et al 2020, Smith et al 2020).
Nationally Determined Contributions (NDCs) communicate countries' contribution to meeting the Paris Agreement (United Nations 2015).Few countries included specific SLCP mitigation in their first NDCs (Malley et al 2022).The Paris Agreement includes a 5-year cycle for countries to update their NDC and increase their climate change mitigation ambition.The inclusion of SLCPs alongside carbon dioxide reductions is one opportunity to increase ambition (CCAC SNAP 2019).To achieve the Paris Agreement, climate change mitigation ambition needs to be increased.Initial pledges were estimated to result in over 3 °C of warming (Rogelj et al 2016, Robiou Du Pont et al 2017), and updated pledges are consistent with 2.4 °C or 'just under 2 °C' (Climate Action Tracker 2021, Meinshausen et al 2022).
In addition to ambition, the need for transparent, and implementable NDCs has also been identified and emphasised, to ensure that NDC targets are realised (Pauw et al 2018, Pauw andKlein 2020).In the context of including SLCP mitigation within NDCs, there are a lack of practical examples as to how countries can submit NDCs that effectively commit to action to reduce SLCPs that are (i) ambitious, and in line with the mitigation necessary to limit global temperature increases to 1.5 °C (IPCC 2018(IPCC , 2021)), (ii) realistic, with a clear plan of the resources required and how the commitment can be achieved (in this context, resources may include technical, human, knowledge and financial, among others), and (iii) additional to necessary reductions in CO 2 emissions.Using these three concepts as criteria for the effective inclusion of SLCPs within NDCs, the aim of this paper is to provide insights into the following questions: • How can countries develop ambitious and realistic targets to reduce SLCPs in their NDCs that are additional to commitments on long-lived GHGs?
• What elements of the planning process are most important for the development of such SLCP targets in NDCs?
To explore these questions, the 2020 NDC update of Colombia is used as a case study.Colombia's first update to their NDC committed to a 51% reduction in GHG emissions in 2030 compared to a 2010 baseline scenario, in line with a long-term vision for net zero emissions by 2050.Colombia also committed to a 40% reduction in black carbon emissions in Colombia by 2030 compared to 2014 levels, making it one of the most ambitious goals to reduce black carbon within NDCs globally (Government of Colombia 2020).Colombia's NDC states that this target was integrated into its updated NDC due to the impact that black carbon has on air pollution in addition to climate change and therefore allows Colombia's climate change actions to have local public health benefits considering that more than 15,000 premature deaths are attributable to air pollution in Colombia with a cost of around 1.5% of GDP on public finances (2015 estimate) (DNP 2018).Assessing how the Government of Colombia developed this SLCP-focused target, the extent to which it is also realistic and additional to action on GHGs, aims to highlight lessons and practical actions that could be relevant to other countries as they consider how to maximise their climate change mitigation ambition, and simultaneously achieve sustainable development benefits such as protecting public health.The first question is explored by analysing how SLCPs are integrated into Colombia's NDC itself (section 2).The second question anlayses the planning process leading to the NDC targets, which is conceptualised as an Intervention Theory model to identify the key elements of the planning process leading to integration of SLCPs within Colombia's NDC (section 3).Finally, limitations and possible improvements, relevant for increasing action in Colombia on SLCPs, as well as other countries, are discussed (section 4).

How SLCP mitigation is reflected in Colombia's NDC
2.1.Framework for assessment of SLCP mitigation targets CCAC SNAP (2019) describes a framework for the inclusion of SLCP mitigation and air pollution co-benefits within NDCs.The framework is centred on four 'opportunities' for including SLCPs within an NDC target, for which different options are outlined to achieve these.Emphasised in this framework is the identification of specific mitigation measures that can reduce SLCPs so that targets are informed by actions that can achieve them.The four opportunities are (i) include mitigation measures on methane and HFCs in NDC, (ii) include mitigation measures on black carbon in NDC, (iii) include mitigation measures to reduce CO 2 in NDCs that contribute to achieving air quality goals, and (iv) align action to achieve the NDC with other plans and strategies.To evaluate Colombia's NDC in terms of its effectiveness at integrating SLCP mitigation, we used this framework to assess how (i) ambitious, (ii) realistic and (iii) additional to GHG reductions the NDC was in terms of SLCP mitigation.To evaluate these three criteria the framework was used as follows to answer the following questions: • Ambition: How many of the opportunities outlined in the framework were included in the NDC to reduce SLCPs?
• Realistic: Were the opportunities linked to concrete mitigation measures to reduce SLCPs?
• Additional: Were the inclusion of opportunities for SLCP mitigation in the NDC clearly additional, rather than an alternative to CO 2 mitigation?
There have been a variety of definitions for these three criteria across climate policy, including NDC evaluation frameworks.Frameworks to evaluate aspects of NDCs fall into two categroies, those that evaluate how the NDC reflects the central purpose of NDCs, as set out in the Paris Agreement, i.e. to reduce greenhouse gas emissions consistent with the Paris Agreement (Fransen et al 2017, Höhne et al 2018, King and Van Den Bergh 2019, WRI and UNDP 2019, Peterson et al 2023), and those that evaluate how NDCs consider other issues that are not the central purpose of an NDC, e.g.sustainable development, human health etc. (Iyer et al 2018, Dickin et al 2020, Dasandi et al 2021, Mantlana et al 2021).For those frameworks that assess GHG emission reductions included within NDCs, ambition is often defined only in terms of the magnitude of GHG emission reduction targets.For example, WRI and UNDP (2019) states that an 'enhanced' NDC is more ambitious if when fully implemented it results in lower cumulative greenhouse gas emissions than the full implementation of the previous NDC.This definition of ambition is also used in frameworks that assess the ambition of other climate policies and plans, such as those submitted by subnational and non-state actors (Hale et al 2021).
Ambition is defined differently here because reducing short-lived climate pollutants is not an explicit requirement of NDCs (although SLCPs such as methane and hydrofluorocarbons are also greenhouse gases.Here, ambition is the scope of actions included within an NDC document to achieve a goal (reducing SLCPs) that is not explicitly required by the Paris Agreement.This definition reflects that there are multiple pollutants grouped as SLCPs, and multiple ways by which an NDC could state how these will be achieved (CCAC SNAP 2019).Within this definition, an NDC is considered to contain more ambition to reduce SLCPs if it includes actions that achieve reduction across a broader set of SLCPs.This definition of ambition does not explicitly assess the magnitude of SLCP emission reductions committed to within the NDC, as previous frameworks have defined ambition in relation to GHGs.However, in contrast to GHGs, where the majority of NDCs submitted a quantitative reduction target (UNFCCC 2021), only one NDC was submitted pre-2020 with an SLCP reduction target (Malley et al 2022).The low inclusion of SLCP-related actions in the initial round of NDCs means that assessing the ambition of post-2020 NDCs (such as Colombia's submitted in December 2020) using the definition of ambition in this work will identify NDCs that, if fully implemented, would lead to larger SLCP emission reductions compared to the previously submitted NDC.Within frameworks that outline how the ambition of NDCs can be enhanced, Fransen et al (2017) provides broad definition of actions that constitute enhanced GHG mitigation ambition, including adopting new GHG emission reduction, or adopting a new sectoral non-GHG target.These types of actions that have been defined as enhancing 'ambition' regarding GHG emission reductions are the most comparable with the definition of ambition used here for SLCP mitigation.
The definition of ambition used here is consistent with previous frameworks for evaluating how non-GHG activities are included within NDCs.For example, multiple studies have assessed the extent to which sustainable development goals (SDGs) are reflected in NDCs.In these cases the number of linkages to different SDGs is often used to identify the breadth of integration within NDCs, comparable with the evaluation of 'ambition' in this work of the number of SLCP reduction opportunities that are reflected in NDCs (Iyer et al 2018, Dickin et al 2020, Mantlana et al 2021).
The second criteria for evaluating the inclusion of SLCPs in NDCs was whether the inclusion of SLCP reductions was realistic, defined as whether reductions in SLCPs were linked to concrete mitigation measures that could achieve SLCP emission reductions.Previous frameworks to evaluate the likliehood of NDC implementation include quantifying the probability of achieving an NDC target based on quantified 'ambition gaps' and 'implementation gaps' (Jin 2023).Different definitions of the 'feasibility' of climate change plans, including NDCs, have been defined.Frameworks assessing feasibility include assessment of the technical potential, i.e. whether the proposed initiative can lead to emission reductions to achieve a target, and other elements necessary for actual implementation, e.g.sometimes referred to as 'initiative feasibility', i.e. the likliehood of the action being adopted by those who can achieve emission reductions, and 'behavioural plasticity', the likliehood of the initiative inducing changes in people's behaviour (Nielsen et al 2020, Stern et al 2022, 2023).In this paper, realistic is defined only whether an NDC identifies specific actions that can lead to SLCP reductions.This is only one component of the broader definition of feasibility used in other climate policy evaluation frameworks (Stern et al 2023), but understanding the proposed initiatives to achieve SLCP emission reduction is nevertheless a prerequisite to developing understanding of their feasibility, taking into account broader societal, political, economic and other factors than their technical SLCP reduction potential.
The final criteria evaluated here, additionality, is not commonly used within other climate policy frameworks, particularly those focussed on greenhouse gases within NDCs.The inclusion of this criteria reflects the specific, and different climate responses of GHGs and SLCPs.When SLCPs were first being considered within climate policy development their relatively shorter atmospheric lifetimes compared to long-lived GHGs means that actions to reduce SLCP emissions (i) can reduce global temperature increases in the short-term (Shindell et al 2012), and (ii) cannot be a substitute for reductions in long-lived GHGs (Bowerman et al 2013).Some argued that action on SLCPs could delay action on carbon dioxide reductions (Myhre et al 2011), while other recent studies have noted some evidence for the fungibility of SLCPs with GHGs in NDCs (Low and Boettcher 2020).This final criteria is therefore a necessary criteria of this framework to assess whether the efforts to reduce SLCPs, which may be ambitious, and realistic, are not included at the expense of strong targets to reduce long-lived GHGs.

Colombia's target to reduce black carbon emissions
Colombia submitted its first NDC in 2018 (Colombia Ministry of Environment and Sustainable Development 2018).Total GHG emissions were estimated to be 224 million tonnes CO 2 -equivalent in 2010, and 335 million tonnes in 2030 in the baseline scenario.The first NDC pledged an unconditional 20% reduction in national total GHG emissions in 2030 compared to a baseline scenario, with a conditional commitment to increase from 20% to 30% reduction subject to international support.The only reflection of SLCPs in the 2018 NDC was that methane and HFCs were two of the GHGs included in the scope of the NDC target, without specifying specific reductions.
Colombia's 2020 NDC update incorporates three of the four opportunities to integrate SLCPs and air pollutants from CCAC SNAP (2019) (Government of Colombia 2020).Opportunity 1 is the inclusion of specific HFC and methane mitigation measures.Colombia's 2020 NDC does not set specific targets for methane or HFC mitigation, but these SLCPs are included in the overall GHG reduction target, which is increased compared to the 2018 NDC.Total GHG emissions were estimated to be 234 million tonnes CO 2 -equivalent emissions in 2015, and 346 million tonnes in 2030 in the baseline, 3% higher than the 2018 NDC estimates.The GHG reduction target was increased to a 51% reduction compared to the 2030 baseline emissions, i.e. a maximum GHG emission in 2030 of 169.44 million tonnes CO 2 -equivalent emissions.An additional update is the detailed description of 148 mitigation measures that will achieve the overall GHG reduction target including those that specifically target methane and HFCs.This update allows assessment of the contribution of methane and HFC mitigation to achieving the overall GHG reduction target.Table 1 includes all mitigation measures that explicitly target SLCPs.The six actions that target major methane and HFC sources were estimated to reduce overall 16.7 million tonnes CO 2 -eq emissions in 2030 compared to the baseline, equivalent to 9% of Colombia's updated GHG reduction pledge.This is likely an underestimate of the total contribution of SLCP mitigation to achieving Colombia's GHG mitigation pledge, as actions that target CO 2 emissions may also reduce methane that is coemitted (e.g. from biomass combustion).
Opportunity 2 in the CCAC SNAP (2019) framework is the inclusion of specific actions that target major sources of black carbon.No information on black carbon was included in Colombia's 2018 NDC.A supplementary target, i.e. in addition to the overall GHG reduction, to reduce black carbon emissions by 40% in 2030 compared to 2014 levels was included in Colombia's 2020 NDC update, i.e. to reduce black carbon emissions from 15,325 tonnes in 2014 (excluding forest fires) to 9195 tonnes by 2030.The mitigation measures to achieve the black carbon target are explicitly outlined in the NDC, and include 3 black carbon-specific measures (table 1).These measures reduce black carbon emissions in addition to black carbon emission reductions that result from implementation of GHG mitigation measures.
The third opportunity is the inclusion of mitigation measures that reduce CO 2 but that simultaneously reduce SLCPs and air pollutants.Colombia's NDC explicitly identifies that the black carbon target will be in part achieved through the implementation of GHG mitigation measures, specifically those that target panela production, brick production, and more efficient biomass cookstoves (table 1).In addition, many of the other CO 2 mitigation measures will implicitly lead to reductions in other pollutants, for example the penetration of electric vehicles, energy efficiency measures and increases in renewable electricity generation.
Therefore, regarding the ambition of how SLCPs have been included in Colombia's NDC, three of the four approaches have been utilised, reflecting a broad consideration of SLCPs within the NDC.A wide range of actions covering methane, HFCs, and black carbon emissions have been covered, and not just one SLCP.The methane and HFC mitigation measures contribute to a substantially more ambitious GHG reduction target compared to the 2018 NDC, as outlined above, as well as a new supplementary black carbon target.While black carbon emissions would be decreased by the achievement of Colombia's 2018 NDC, due to the overlapping sources of GHGs and black carbon, and other air pollutants, this was not quantified.The black carbon reduction target included in the 2020 NDC therefore constitutes a more explicit commitment to reduce black carbon compared to Colombia's 2018 NDC.It is also among the largest black carbon emission reduction targets in any NDC.Several countries have included SLCPs and black carbon in their NDCs, but only Colombia, Mexico and Chile have included quantitative targets.Colombia's target, a 40% reduction compared to 2014 levels, compares with a 51% black carbon emission reduction in 2030 compared to a baseline scenario in Mexico (Government of Mexico 2016), and a 25% reduction compared to 2016 levels in Chile (Government of Chile 2020).
The key update compared to the 2018 NDC that increases how realistic Colombia's NDC is, is the identification of the specific mitigation measures that will achieve the GHG and black carbon emission reduction targets.This clarifies how the reductions in SLCPs will occur, what actions need to be taken, and the contribution each action will make to the overall achievement of targets (shown in table 1).For each mitigation measure, the NDC specifies details on their implementation, including financing mechanisms, co-benefits and alignment with sustainable development goals, and the key institutions responsible for implementation (Government of Colombia 2020).While describing these details does not guarantee their implementation, it allows institutions within and outside Colombia to understand where resources need to be directed, and provides the basis for detailed monitoring of NDC implementation.(1) In Colombia's NDC, Global Warming Potentials (GWP) from the 5th IPCC Assessment Report were used to convert emissions to carbon dioxide equivalent (i.e. for Methane, a GWP of 28 was used).
(2) Emission reduction potentials are taken from Colombia's NDC and is compared to 2030 baseline scenario emission (3) CO2-eq emission includes methane and others GHG.
Finally, the mitigation measures included in Colombia's NDC are clearly additional to those included to reduce long-lived GHGs.The specification of the mitigation measures allows the contribution of measures which target methane and HFCs to achieve the overall GHG reduction target to be determined, in addition to those measures that target long-lived GHGs.Two arguments have been outlined against defining a target to reduce black carbon, on top of those to reduce GHGs.Firstly, that black carbon emission reductions are achieved automatically when CO 2 mitigation measures are implemented, and therefore the black carbon target does not lead to additional emission reductions over and above those achieved from implementing a GHG target.Secondly, that a black carbon reduction target may divert attention, or mask lower ambition on GHG mitigation (Myhre et al 2011, Bowerman et al 2013, Allen 2015, Low and Boettcher 2020).In Colombia, a portion of the black carbon target will be achieved through the implementation of GHG mitigation measures, with the key measures that have GHG and black carbon reductions highlighted in the NDC (table 1).However, there is also clear additionality from the black carbon target because of the inclusion of three additional measures (i) Euro VI vehicle emission standards, (ii) Emission standards for off-road machinery and (iii) reducing open burning of agricultural residues, that specifically target major black carbon sources, and which were not selected because of their effectiveness in reducing CO 2 emissions.The black carbon target is also included alongside a GHG reduction target for 2030 that is aligned with a long-term net-zero vision by 2050.Therefore, the inclusion of a black carbon target has not resulted in a GHG reduction target that is less ambitious than other countries committed to decarbonisation by 2050, but without specific provisions for SLCP mitigation within their NDCs (UNFCCC 2021).

Framework to conceptualise NDC update process for black carbon in Colombia
To assess how a planning process can be structured to effectively integrate SLCPs within NDCs, its key elements are conceptualised as an 'intervention theory' model (Linnér et al 2012, Malley et al 2021).Intervention theory is a conceptual framework that has been used to develop models of policy or decision making processes, including environmental policy processes (Chen 2005, Linnér et al 2012, Malley et al 2021).An intervention theory model aims to assess the effectiveness of different activities in achieving the intended goals.An intervention is defined here as the overall group of activities undertaken with the intention of achieving a specific goal.In this work the goal is 'the development of ambitious, realistic targets to reduce SLCPs that are additional to actions to reducing CO 2 .The intervention encompasses all activities within Colombia related to SLCPs that have been implemented since 2012, when Colombia joined the Climate and Clean Air Coalition and began implementing activities on SLCPs.
The intervention theory model decomposes an intervention into three components that interact and determine the contribution and causes of achieveing (or not) the intended goal (Chen 2005).Firstly, the context describes the social, political, economic, and/or physical systems within which the intervention takes place.Here, the context encompasses the NDC update process, the responsibilities and relationships between stakeholders (e.g.Government departments, civil society, NGOs), the major source sectors emitting SLCPs, GHGs and air pollutants, and the existing regulatory, legal, monitoring and enforcement frameworks in place to control emissions.
The second component is the change model, which outlines how an intervention and its constituent activities are intended to achieve its goal in a given context.The change model describes the different activities, and the outputs, and outcomes produced from each activity (or group of activities) to map the linkages and causal processes that achieve the overall goal.The change model identifies the individual activities that Colombia has undertaken on SLCP planning, and the linkage between activities that resulted in ambitious, realistic and additional SLCP targets being included in Colombia's 2020 NDC.
Finally, the third component is the action model.The action model describes the specific actions, and those who take them, that produce the outputs and outcomes for each component of the change model.The change model describes the overarching 'theory of change' as to how the goal of the intervention is achieved, i.e. how the activities 'add up' to achieve the overarching goal.The action model focuses on the practical steps by which the activities are actually implemented, including what actions are taken to achieve the outputs, and who undertakes them.
The intervention theory model was developed through the experience of the authors, who have been involved in the development of Colombia's national Short-Lived Climate Pollutant planning in different roles and for different time periods.The author's experience includes Ministry of Environment and Sustainable Development officials leading the initial SLCP planning projects that culminated in the development of Colombia's National SLCP Strategy, and those coordinating the development of Colombia's NDC.It also includes international partners who have provided technical, administrative and project management support to these initiatives.These different perspectives were used to build an initial intervention theory model which was then evaluated against documentation of the SLCP Planning process and NDC update process undertaken between 2016 and 2022.
The inclusion criteria for relevant documents were all those developed within two initiatives undertaken by the Ministry of Environment and Sustainable Development of Colombia related to SLCPs.The first was projects, implemented between 2016 and 2022, funded by the Climate and Clean Air Coalition to enhance national Short-Lived Climate Pollutant mitigation planning in Colombia.Documents reviewed were Colombia's National SLCP Strategy (Colombia Ministry of Environment and Sustainable development 2020), the National Black Carbon Emission Inventory (IDEAM 2020), and a black carbon mitigation assessment undertaken in 2020-2021.The second initiative was the process to enhance Colombia's NDC, undertaken between 2020 and 2021.Documents reviewed included Colombia's updated NDC (Government of Colombia 2020), Annexes to the updated NDC on the mitigation component, and a World Health Organisation technical report on the air pollution health benefits from implementation of Colombia's updated NDC (WHO 2023).These documents were developed during each planning process, and written by a broader range of authors than the researchers included within this work.They therefore provided a useful resource against which to evaluate, and adjust the intervention theory model.The documents were reviewed for all references to Short-Lived Climate Pollutants and related terms (i.e.air pollution, health, Climate and Clean Air Coalition, methane, black carbon, hydroflurocarbons, tropospheric ozone) to determine (i) how SLCPs were represented in the NDC itself, and (ii) how SLCPs were considered during the process for NDC development.The information extracted from each document was then compared against the initial change and action models developed by the author team to either (i) confirm the chain of activities, outputs, and outcomes that achieved the overall goal, and the specific activities undertaken within each intervention, or (ii) revise the model based on additional information extracted from the documents.

Key elements of planning process leading to SLCP integration in Colombia's NDC
Figure 1 summarises the intervention theory model for the goal of establishing ambitious, realistic, and additional targets for SLCPs in Colombia's NDC.The context highlights that, in common with many countries, there are substantial overlap in the sources of SLCPs, GHG and air pollutants, and major SLCP sources including residential cooking, transport, agriculture, and brick production (IDEAM 2020).This shows the key sectors where taking action can lead to substantial national-level reductions in SLCPs and therefore where target-setting should focus.
The second key element of the context are the existing structures, processes and institutions in Colombia that manage climate change and air quality planning.SLCP mitigation is inherently, and principally about integrating the agendas of these two processes, to ensure that the actions, policies and measures put in place for mitigating climate change, and for improving air quality are aligned, and account for possible trade-offs.Given the existing institutions responsible for air quality and climate change, the context emphasises the need to ensure these two institutions communicate and align their agendas.
Finally, the context also highlights the broader climate change planning and decision-making process to determine Colombia's NDC targets.Different models used for setting national climate change mitigation targets include 'top-down' approaches in which a target is politically defined, and 'bottom-up' approaches in which targets are determined through the compilation/aggregation of the emission reduction potential of mitigation actions (CCAC SNAP 2019, WRI and UNDP 2019, Hermansen and Sundqvist 2022).In Colombia, for the 2020 NDC update, a hybrid approach was used.The Office of the Presidency was responsible for the overall NDC targets, and sectoral ministries were responsible for identifying mitigation measures to reduce emissions.The Ministry of Environment was responsible for the evaluation of emission reductions achievable from implementing these mitigation measures.This could inform recommendations to the Presidency on climate change mitigation ambition achieveable from a set of nationally-defined mitigation measures.The implication from this context is the need to (i) define and evaluate specific mitigation measures in terms of their SLCP emission reduction potential, and (ii) engage sectoral ministries in defining these mitigation measures, given their responsibility for identifying, and ultimately implementing mitigation measures underpinning climate change mitigation targets.
The change model highlights three key outcomes necessary to achieving an SLCP target in the NDC (figure 1).Obtaining broad agreement to include an SLCP reduction target within Colombia's NDC is required because the Paris Agreement does not require specific SLCP reduction targets (United Nations 2015).Consequently, stakeholers needed to that it was useful and appropriate to set SLCP-focussed targets.The key activity that achieved this agreement was the development, endorsement and publication of a National SLCP Strategy (Colombia Ministry of Environment and Sustainable Development 2020).
The development of Colombia's National SLCP Strategy followed a four-year planning process in which the Ministry of Environment engaged a broad range of stakeholders to describe SLCPs and the link between air pollution and climate change mitigation.The National SLCP Strategy set objectives and goals to integrate SLCP mitigation into national planning and policy-making processes.One of these objectives was evaluation of mitigation measures to reduce black carbon, to provide the basis for the integration of black carbon mitigation within climate change planning.Other objectives included quantification of black carbon emissions in national greenhouse gas inventories, so that any target can be tracked effectively, and the development of cost-benefit assessments to evaluate the costs and the benefits (economic and public health) of implementing these measures.These objectives also highlighted the need to enhance capacity to undertake these assessments, e.g. through expanding human resources and training of staff, within the Ministry of Environment (as the main entity responsible for the implementation of the SLCP strategy) and affiliated institutions, e.g.empowering subnational entities to increase efforts to reduce black carbon emissions Agreement of the goals within Colombia's National SLCP Strategy was particularly important to obtain from the two divisions within the Ministry of Environment responsible for air quality and climate change mitigation, due to the overlapping contribution SLCP mitigation makes to both of these issues.The National SLCP Strategy includes objectives and targets that align the air quality and climate change planning processes.For example, goals and objectives include the integration of the black carbon emission inventory into the national GHG emission inventory, which allows for the consistent assessment of GHGs, SLCPs and air pollutant emissions.Simultaneously, SLCP planning has been integrated into air quality planning, and facilitated alignment between solving these two problems.In 2019, Colombia released their first National Air Quality Strategy.In this strategy, the national black carbon and other air pollutant emission inventory was the basis for identifying the major air pollutant emission sources that require control, meaning that the basis for the actions in the strategy is consistent with the underlying information used to set the NDC black carbon target (see below) (Colombia Ministry of Environment and Sustainable development 2019).
The implication of formalising these objectives within a National SLCP Strategy was that the Ministry of Environment is now responsible for their implementation.This responsibility includes publicly reporting and monitoring progress on implementation, creating accountability for achieving the objectives, and empowering sub-national entities to increase efforts to reduce black carbon emissions.
The National SLCP Strategy facilitated inclusion of an SLCP reduction target in the NDC by recommending a potential target level based on the evaluation of specific mitigation measures that could reduce black carbon emissions (figure 1).A mitigation assessment was undertaken that identified the reduction in black carbon emissions from a discrete set of mitigation measures.This mitigation assessment was one of the key objectives included in Colombia's National SLCP Strategy (Colombia Ministry of Environment and Sustainable development 2020).To quantify the black carbon emission reductions that could be recommended as a possible target in the NDC, a set of mitigation measures were first identified.These included both the GHG mitigation measures put forward by sectoral ministries as part of the NDC revision process and additional measures targeting black carbon, identified by the Ministry of Environment, and ministries responsible for key black carbon emitting sources (e.g.transport).The black carbon emission reduction potential of the selected mitigation measures was quantified (table 1).
To recommend a black carbon target level, a clear reference point was needed.For GHGs, the regular development of national GHG emission inventories provides this reference (even if the GHG target is expressed compared to a theoretical 2030 baseline emission value, the national GHG emission for a historical year is usually the starting point for such a projection).The development and endorsement of a national black carbon emission inventory by the institution in Colombia responsible for the national GHG emission inventory (the Institute for Hydrology, Meteorology, and Environmental Studies (IDEAM)) provided an equivalent reference for a black carbon target (IDEAM 2020).This is shown in the 2020 NDC, in which the black carbon reduction target is a reduction of 40% compared to 2014 emission levels as quantified in the national black carbon emission inventory (Government of Colombia 2020).An authoritative national institution such as IDEAM developing these black carbon emission estimates meant that as well as providing a reference emission, there is a national institution capable, and responsible, for updating the black carbon emission inventory to monitor against the target during NDC implementation.
Finally, once the technical analysis recommended a potential target level, this needed political and public endorsement.The draft NDC was submitted to public consultation before being sent to the Office of the Presidency for final approval and endorsement.This high-level political approval process increased the magnitude of the black carbon reduction target, beyond the level recommended based on evaluation of the reductions achievable from the mitigation measures identified.This, therefore, provided additional ambition to reduce SLCPs, alongside additional ambition to reduce GHGs, within the final NDC.
These activities within the change model could be applied in other countries to define SLCP targets, and could lead to broader enhancement of NDCs.Some of the activities identified as contributing to Colombia's SLCP targets have been shown in other assessments to be important determinants of enhanced GHG reduction targets within NDCs.Previous studies, analysing hundreds of NDCs, identified that broad stakeholder engagement, including engagement with civil society organisations as being a significant factor in countries submitting enhanced GHG reduction targets within their NDCs (Tørstad et al 2020, Peterson et al 2023).This indicates that there is an opportunity for countries where stakeholder engagement and public consultation support the development of GHG targets in NDCs to simultaneously support the definition of SLCP targets.Conversely, where consultations are less prevalent in climate change planning, the ability to integrate discussion of SLCP target within consultative processes is more limited.Other areas where the process undertaken in Colombia may be challenging to replicate in other countries is in the development of technical assessments of emission reductions, which have been highlighted as a barrier to the development of GHG reduction targets (Vaidyula and Hood 2018), and which many countries requested international assistance during the last round of NDC revisions (2020-2022) (Victor et al 2022).
The action model provides a more detailed set of practical lessons that could be used by other countries to enhance climate change mitigation ambition and achieve local benefits through actions that reduce SLCPs.Three key practical insights emerge that can aid in setting achievable, ambitious targets on SLCPs from Colombia's experience (figure 1).
1. National ownership of planning and analysis is essential: Firstly, who undertakes the different components of the interventions matters.In many low-and middle-income countries, national and international consultants commonly develop the technical assessments that underpin the definition of targets and mitigation components in climate change plans.A limitation of this approach is that often different consultants undertake assessments for different planning processes (e.g.NDCs, National Communications, Biennial Update Reports, etc.).This limits consistency between assessments and does not contribute to the strengthening of capacity within national institutions to undertake these assessments within the country.In Colombia, the national black carbon emissions inventory was undertaken by the national institution responsible for emission inventories (IDEAM).Their development and endorsement of the national black carbon emission inventory provided a strong basis for i) understanding the major sources of black carbon where mitigation actions needed to be focussed, and ii) the reference emission level against which a target could be set.This instilled confidence across stakeholders that a black carbon mitigation target was developed taking into account national circumstances, and a commitment that the inventory will be regularly updated, providing the basis for monitoring the progress on the implementation of the black carbon target.The importance of national institutions leading key elements of the process to determine SLCP targets is consistent with studies analysing the credibility of NDCs.The quality of national political institutions was highlighted as among the key factors that determine the credibility of an NDC (Victor et al 2022).National ownership over the planning process to develop SLCP targets may be challenging for many countries.During the last round of NDCs revisions, countries with lower human development index scores were more likely to request international support for the NDC development (Mehrotra and Benjamin 2022).Ensuring that this type of support directly contributes to enhancing the capacity of national institutions is important to enhance the credibility of GHG reduction targets.The case study for Colombia indicates that building capacity in national institutions could also support establishment of SLCP targets.However, as SLCP emission reductions contribute to direct benefits where action is taken, inclusion of SLCPs within this capacity building may enhance the sustainability of capacity building, as national institutions are motivated to achieve local benefits within their jurisdiction.
2. Long-term planning and sustainable capacity enhancement is needed: While the NDC revision process spanned just over a year between 2019 and 2020, the intervention for the black carbon target lasted over 8 years.A focus on long-term planning and strengthening capacity in national institutions are necessary for the establishment of realistic SLCP targets (or other aspects of low-emission development planning) to have broad support.The importance of the black carbon emission inventory to set the target is outlined above, and its development started in 2016, before being published in 2020.The development of the technical assessment of emission reductions from mitigation measures involved training workshops including the Ministry of Environment and other stakeholders and technical support from international institutions to ensure that it could be completed by the responsible national team.A focus on long-term planning and strengthening capacity in national institutions helps to ensure that when targets are set there is broad support because stakeholders have been sensitized, and contributed to, the recommended target.It also ensures that systems are in place for the target to be operationalized and implemented, making it more realistic than a target that has been defined solely within a short-term planning process focusing on the NDC in isolation.Ongoing initiatives to build capacity on SLCP mitigation planning suggest that there is an increasing group of countries where the capacity of national institutions could emulate the SLCP planning in Colombia (CCAC SNAP 2019, Malley et al 2021).
3. A package of mitigation measures is essential to robustness and implementation of SLCP target: The focus on a clear package of measures to reduce black carbon emissions is a common theme throughout the activities of the change model.In Colombia's National SLCP Strategy, one objective is to identify and evaluate the effectiveness of measures to reduce black carbon.Once identified, the initial level of the recommended NDC black carbon target was based on the black carbon emission reductions achieveable from a set of mitigation measures (table 1).This emphasizes that the target is realistic, because there is a clear basis for how the target can be achieved.It also demonstrates the additionality to CO 2 mitigation because of the additional measures included specifically to reduce black carbon emissions.Following review by the Presidency, the target ambition was increased.The existing capacity within Colombia for the assessment of black carbon emission reductions for particular mitigation measures means that additional mitigation measures can be identified and evaluated to assess how the additional emission reductions can be realised.

Limitations, improvements, and next steps for setting targets on SLCPs in climate change commitments
While the process summarised in the intervention theory model led to the ambitious, realistic, and additional inclusion of SLCPs within Colombia's 2020 NDC, there were also limitations in the SLCP planning process and NDC update which could be overcome to make the planning process more effective.Firstly, the assessment of black carbon emission reductions was undertaken separately from the GHG mitigation assessment.This resulted in two teams developing parallel mitigation assessments, including data collection, implementing emission modeling methods, etc. which have a substantial overlap for GHGs and black carbon.It also meant that an extra step in the black carbon mitigation assessment was necessary to compare the assessments to ensure that the black carbon emission results were consistent with those for GHGs.Undertaking an integrated assessment of GHG, SLCP, and other air pollutant mitigation in a single assessment would increase efficiency, and ensure consistency with the emission reduction estimates for different pollutants and remove the need for comparison.It would also facilitate identifying those strategies that can simultaneously be beneficial for mitigating GHGs and SLCPs (Kuylenstierna et al 2020, Nakarmi et al 2020).
Secondly, within the SLCP planning processes, the reduction in emissions of other air pollutants was not quantified or included within the revised NDC.Strategies to mitigate SLCPs can also reduce emissions of other air pollutants (and in some cases GHGs like CO 2 ) that are emitted from the same source.Therefore, the simultaneous reduction in other air pollutants like organic carbon, directly emitted PM 2.5 particles, nitrogen oxides, sulfur dioxide, and volatile organic compounds, makes a substantial contribution to determining the overall impact on air pollution and climate change (e.g cooling effects on the atmosphere) from implementing SLCP strategies.Therefore, a complement to an NDC black carbon target would be to also include the expected change in emissions of other air pollutants, and GHGs, that would result from its achievement, seen in other SLCP mitigation assessments (Kuylenstierna et al 2020, Agbossou et al 2022).
Since the publication of Colombia's NDC, the reduction in emissions of other air pollutants has been quantified.In addition to providing a more comprehensive overview of the effect of achieving Colombia's black carbon target on a fuller range of atmospheric emissions, it also allows for the quantification of societal, economic and public health impacts from achieving this target.The quantification of all GHG, SLCP, and air pollutant emission reductions allows changes in exposure to air pollutants to be quantified, and the resultant changes in incidence of diseases that are associated with air pollution exposure (Kuylenstierna et al 2020).Undertaking this health impact assessment demonstrates directly the local benefits that can be achieved in Colombia from implementing their international climate change commitment, helping to build a broader coalition of support for its implementation (Linnér et al 2012, Malley et al 2021).

Conclusions
Mitigation of Short-Lived Climate Pollutants (SLCPs) provides a clear way to increase national climate change mitigation ambition, while simultaneously achieving local development benefits by improving air quality and protecting public health.Inclusion of SLCP mitigation in NDCs formalises this type of action within climate change mitigation pledges, and help facilitate access to climate finance for activities that achieve local benefits.This paper has demonstrated, using the NDC update for Colombia, how such targets on SLCPs can be developed and included within NDCs as ambitious, realistic targets that are additional CO 2 mitigation.This includes in particular ensuring that targets are underpinned by specific mitigation measures to achieve them.This allows the contribution of reductions in methane and HFCs (SLCPs that are also GHGs) to achieving an overall GHG reduction target to be clarifiedand ensures that targets are realistic, as there is a clear program of actions to achieve them.
In Colombia, the establishment of SLCP mitigation targets within the NDC was a result of an intervention in SLCP planning that focussed on long-term planning and strengthening capacity within national institutions.Producing Colombia's National SLCP Strategy before the NDC raised awareness among relevant stakeholders of the need and opportunity for actions on SLCPs.The development of key technical resources on SLCPs, such as the national black carbon emission inventory provided a nationally recognized reference point against which targets could be set.Now that an SLCP target has been set in Colombia's NDC, the long-term planning, and capacity built means that Colombia is well positioned to implement this target, because stakeholders have endorsed and identified the specific measures to achieve it, and key national institutions have the technical capacity to monitor the implementation of the target, through regular updating and reporting of the national black carbon emission inventory.As other countries consider the inclusion of SLCP mitigation within NDCs, the experience in Colombia emphasizes the advantage of doing so by i) ensuring that all relevant stakeholders, including implementing agencies, are aware, endorse and contribute to setting the level of the target, and ii) putting in place programs and activities to build long-term capacity within national institutions to evaluate the effect of mitigation actions to reduce SLCPs, mitigate climate change and improve air quality so that any target set is realistic, and to monitor the implementation once the target has been set.

Figure 1 .
Figure 1.Overview of intervention theory model for SLCP integration into Colombia's NDC.

Table 1 .
Mitigation measures included in Colombia's NDC that specifically target major source of SLCPs (methane, HFCs and black carbon).