About half of the anthropogenic CO2 emissions remain in the atmosphere and half are taken up by the land and ocean1. If the carbon uptake by land and ocean sinks becomes less efficient, for example, owing to warming oceans2 or thawing permafrost3, a larger fraction of anthropogenic emissions will remain in the atmosphere, accelerating climate change. Changes in the efficiency of the carbon sinks can be estimated indirectly by analysing trends in the airborne fraction, that is, the ratio between the atmospheric growth rate and anthropogenic emissions of CO2 (refs. 4,5,6,7,8,9,10). However, current studies yield conflicting results about trends in the airborne fraction, with emissions related to land use and land cover change (LULCC) contributing the largest source of uncertainty7,11,12. Here we construct a LULCC emissions dataset using visibility data in key deforestation zones. These visibility observations are a proxy for fire emissions13,14, which are — in turn — related to LULCC15,16. Although indirect, this provides a long-term consistent dataset of LULCC emissions, showing that tropical deforestation emissions increased substantially (0.16 Pg C decade−1) since the start of CO2 concentration measurements in 1958. So far, these emissions were thought to be relatively stable, leading to an increasing airborne fraction4,5. Our results, however, indicate that the CO2 airborne fraction has decreased by 0.014 ± 0.010 decade−1 since 1959. This suggests that the combined land–ocean sink has been able to grow at least as fast as anthropogenic emissions.
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The Python code that was used to assimilate the raw data and perform the analyses is available at https://doi.org/10.5281/zenodo.5617953.
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This research was funded by the European Research Council (ERC) grant number 280061 and the Netherlands Organization for Scientific Research (NWO) (Vici scheme research programme, no. 016.160.324).
The authors declare no competing interests.
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Extended data figures and tables
Extended Data Fig. 1 RCP8.5-projected and observed evolution of atmospheric CO2 growth using our LULCC data.
RCP8.5-projected (background) and observed (forefront) atmospheric CO2 growth over 2010–2020 on the basis of observed concentrations, sources from fossil fuel burning, cement manufacturing and LULCC based on this study. Sink strength is computed as the residual. AF is short for airborne fraction and the numbers indicate what the difference is between observed values and RCP8.5 projections for each component.
Extended Data Fig. 2 Evolution of RCP8.5-projected and observed anthropogenic emissions and atmospheric CO2 growth rate over 2000–2019.
Fossil fuel emissions increased less than projected in RCP8.5 after 2012, but this was partly compensated for by higher-than-projected LULCC emissions in most years.
Extended Data Fig. 3 RCP8.5-projected and observed evolution of atmospheric CO2 growth on the basis of other LULCC datasets.
RCP8.5-projected (background) and observed (forefront) evolution of atmospheric CO2 growth over 2010–2020 on the basis of observed concentrations, sources from fossil fuel burning, cement manufacturing and LULCC on the basis of the GCP (a) and H&N (b). Sink strength is computed as the residual. AF is short for airborne fraction and the numbers indicate what the difference is between observed values and RCP8.5 projections for each component.
This overview shows our method to construct LULCC emissions on the basis of fire emissions in key deforestation zones of GFED4s (1997–2019) and visibility-based Bext anchored to GFED4s for the preceding period. These were supplemented by non-fire emissions including those stemming from peat dynamics in EQAS.
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van Marle, M.J.E., van Wees, D., Houghton, R.A. et al. RETRACTED ARTICLE: New land-use-change emissions indicate a declining CO2 airborne fraction. Nature 603, 450–454 (2022). https://doi.org/10.1038/s41586-021-04376-4
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