The response of terrestrial ecosystem carbon cycling under different aerosol-based radiation management geoengineering

Abstract. Geoengineering has been discussed as a potential option to offset the global impacts of anthropogenic climate change, and at the same time help reach global temperature targets of the Paris Agreement. Before any implementation of geoengineering, however, the complex natural responses and consequences of such methods should be fully understood to avoid any unexpected and potentially degrading impacts. Here we assess the response of different terrestrial biomes in their ecosystem carbon exchange and storage storage under three different aerosol-based radiation management (RM) methods applied on top of the baseline RCP8.5 scenario using an Earth System Model (NorESM1-ME). All three methods used in this study (stratospheric aerosol injection, marine sky brightening, cirrus cloud thinning) target the global mean radiation balance at the top of the atmosphere to that of the RCP4.5 scenario. The three different RM methods investigated in this study exhibit vastly different precipitation patterns especially in the tropical forest biome due to the methodological differences in how the aerosols are applied. This resulted in large variability in global vegetation carbon uptake and storage across the three methods as tropical forest biome contribute the largest to global vegetation carbon uptake and storage. Our findings show that there are unforeseen regional consequences in the biogeochemical cycles under geoengineering and these consequences should be taken into account in future climate policies. Although, changes in temperature and precipitation play a large role in vegetation carbon uptake and storage, our results show that CO2 fertilization also plays a considerable role. We find that changes in vegetation carbon storage under geoengineering application was much smaller than what is exhibited under RCP4.5 scenario that uses climate mitigation efforts by afforestation in the tropics. Hence, it would be important to consider the multiple combined effects and responses of land biomes when applying different strategies to reach the global temperature targets of the Paris Agreement.