The paper trail of the ¹³C of atmospheric CO₂ since the industrial revolution period

The ¹³C concentration in atmospheric CO₂ has been declining over the past 150 years as large quantities of ¹³C-depleted CO₂ from fossil fuel burning are added to the atmosphere. Deforestation and other land use changes have also contributed to the trend. Looking at the ¹³C variations in the atmosphere and in annual growth rings of trees allows us to estimate CO₂ uptake by land plants and the ocean, and assess the response of plants to climate. Here I show that the effects of the declining ¹³C trend in atmospheric CO₂ are recorded in the isotopic composition of paper used in the printing industry, which provides a well-organized archive and integrated material derived from trees' cellulose. ¹³C analyses of paper from two European and two American publications showed, on average, a − 1.65 ± 1.00‰ trend between 1880 and 2000, compared with − 1.45 and − 1.57‰ for air and tree-ring analyses, respectively. The greater decrease in plant-derived ¹³C in the paper we tested than in the air is consistent with predicted global-scale increases in plant intrinsic water-use efficiency over the 20th century. Distinct deviations from the atmospheric trend were observed in both European and American publications immediately following the World War II period.