Emergent constraints on global carbon-climate feedbacks from regional atmospheric aridity

Abstract:

The vulnerability of terrestrial carbon sequestration to increases in fossil-fuel emissions is one of the most important feedbacks in the Earth System. However, the relative importance of temperature and moisture controls on regional terrestrial CO₂ fluxes varies substantially, and it is critical to unravel their roles in carbon—climate feedbacks. Here, we employ the Hierarchical Emergent Constraint (HEC) approach to quantify an emergent relationship between 1) spatially explicit carbon-flux sensitivity to atmospheric aridity and 2) the long-term sensitivity of tropical-land carbon storage to atmospheric aridity, across an ensemble of Earth System Models (ESMs). Our results show that interannual fluctuations in atmospheric aridity, as an important driver of atmospheric water demand for plants, substantially impact the terrestrial carbon sink. Furthermore, this analysis, which is conditioned on observations, results in a substantially lower feedback than predicted by ESMs alone. Finally, we show that a relatively small number of regions have an outsized impact on global carbon—climate feedbacks. Our findings underscore the role of both water and temperature on carbon—climate feedbacks, while the regional attribution provided by the HEC approach points to regions where further investigation of the feedback process might be targeted.