CO2-induced terrestrial climate feedback mechanism: From carbon sink to aerosol source and back
Feedbacks mechanisms are essential components of our climate system, as they either increase or decrease changes in climate-related quantities in the presence of external forcings. In this work, we provide the first quantitative estimate regarding the terrestrial climate feedback loop connecting the increasing atmospheric carbon dioxide concentration, changes in gross primary production (GPP) associated with the carbon uptake, organic aerosol formation in the atmosphere, and transfer of both diffuse and global radiation. Our approach was to combine process-level understanding with comprehensive, long-term field measurement data set collected from a boreal forest site in southern Finland. Our best estimate of the gain in GPP resulting from the feedback is 1.3 (range 1.02-1.5), which is larger than the gains of the few atmospheric chemistry-climate feedbacks estimated using large-scale models. Our analysis demonstrates the power of using comprehensive field measurements in investigating the complicated couplings between the biosphere and atmosphere on one hand, and the need for complementary approaches relying on the combination of field data, satellite observations model simulations on the other hand.