Geoengineering Increases the Global Land Carbon Sink
Researchers from Oak Ridge National Laboratory and the University of Tennessee Knoxville, with collaborators from the National Center for Atmospheric Research, Rutgers University, Cornell University, and Indiana University examined the impacts of stratospheric aerosol intervention (SAI) on terrestrial ecosystems following the Representative Concentration Pathway 8.5 (RCP8.5) during the 21st century, by analyzing results from a large ensemble Earth system model (ESM) simulations. Comparison of simulations with and without SAI show biogeochemical feedbacks from terrestrial ecosystems can alter the atmospheric CO2 trajectory and in turn adjust the SAI effort required to maintain surface temperature at 2020-levels.
Our analysis shows that SAI induces a lower ecosystem respiration rate and diminished disturbance effects, resulting in increased carbon sequestration in terrestrial ecosystems globally. With these terrestrial biogeochemical (BGC) feedbacks considered, an additional 79 Pg C would be stored on land by the end of the 21st century when SAI is applied, yielding as much as a 4% reduction in atmospheric CO2 mole fraction without marine biogeochemical feedbacks. Such atmospheric CO2 reduction due to terrestrial BGC feedbacks could lessen the aerosol injection amount by 1.4 Tg yr-1 at 2097 as a result of cooler temperature consistent with a lower atmospheric CO2 level.
Intervention strategies have been proposed for years as a means to mitigate the warming caused by rising anthropogenic emissions. Among all strategies, stratospheric aerosol proposals draw attention widely because of their relatively low cost for mitigating the surface temperature warming and their evenly-distributed cooling capability around the world. While many publications have examined the impacts of SAI on climate change, very few have investigated the responses and feedbacks of ecosystems under an extreme SAI mitigation strategy. ESMs driven by prescribed atmospheric CO2 concentration defined in emission scenarios such as RCP8.5 could overlook the BGC feedbacks that alter the atmospheric CO2 trajectory and in turn modify the SAI effort required to stabilize surface temperature. Conducting fully coupled and emissions-forced ESM simulations with both marine and terrestrial BGC feedbacks enabled, as well as including stratospheric and tropospheric chemistry, will be necessary to further reduce uncertainties in quantifying SAI impacts on the Earth system.