Carbon dioxide (CO2) emissions from humans are taken up by the atmosphere, land, and ocean. However, the robustness of carbon sinks is unclear, and complex Earth system models are time-consuming to run. This study used a simple global carbon/climate model to track emissions, explore the long-term destination of CO2, and examine the overall implications for carbon cycle dynamics. Researchers found that a quarter of emissions ended up in the atmosphere, while over half are taken up by the land. Land and ocean carbon sinks tend to have stable or increasing CO2 absorption over time.
Hector, a simple global climate model, has a novel carbon tracking feature and fast run time, providing a unique and powerful tool to analyze global carbon dynamics and probabilities through large ensemble runs. As such, this study provides further evidence for the robustness of the land and ocean carbon sinks in a future of intensifying climate change. By identifying emissions sources and sinks that are not differentiable through measurements, this study provides insights into the dynamics of anthropogenic CO2 in the Earth system and emphasizes the importance of future work in this area.
Atmospheric CO2 concentrations have increased as a direct result of human activity. However, the magnitude and future dynamics of land and ocean carbon sinks are not well understood. The observational amount of anthropogenic fossil fuel emissions that remain in the atmosphere (the airborne fraction) is poorly constrained. This work aimed to quantify the sources and controls of atmospheric CO2, the fate of anthropogenic CO2 over time, and any potential trend in the airborne fraction. Researchers used Hector v3.0, a coupled simple climate and carbon cycle model, to track CO2 flowing through the Earth system. By running Hector, researchers found that roughly 52% of emitted CO2 stayed in the atmosphere in the historical period (from 1960 to 2020), consistent with observational studies of the contemporary airborne fraction. These results suggest that current-day land and ocean sinks are not weakening and are continuing to sequester almost half of anthropogenic emissions. By using Hector to model future outcomes, this study also provides insights into the dynamics of anthropogenic CO2 in the Earth system. Model projections indicated that the future percentage of atmospheric CO2 with anthropogenic origins ranged across different CO2 emission scenarios from 39% to 88% in 2100, meaning that atmospheric CO2 is primarily anthropogenic in origin. However, only a quarter of these future anthropogenic emissions ended up in the atmosphere, with over half taken up by land on centennial timescales, highlighting the significance of the land sink in taking up future anthropogenic CO2.