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Contrasting Stratospheric Aerosol Injection Geoengineering with Greenhouse Gas Emission Cuts in Mitigating Human Thermal Stress Globally
Abstract
Greenhouse gas-induced climate change is ongoing, increasingly causing heat-related illness, suffering, and death. While carbon emission reduction is recognized as the main approach of mitigation, geoengineering as an emergency response has gained stronger interests in recent years. Stratospheric Aerosol Injection (SAI) is one proposed method of geoengineering to mitigate rising temperatures in the future decades.
Previous studies on SAI have primarily focused on the impacts on surface temperature and precipitation but have lacked a direct and rigorous assessment of human thermal stress indicators, arguably more relevant to the health outcome of vulnerable populations globally.
Using CESM2-WACCM6 model simulation over the period of 2020 – 2100 from CMIP6’s ScenarioMIP and GeoMIP projects, this paper investigates the spatial and temporal evolution of temperatures and a suite of 5 heat indices under a decarbonization emission pathway (SSP245) and an SAI scenario (G6sulfur), relative to the baseline a climate scenario of continued fossil fuel economic development (SSP585). These indices are carefully chosen to embody the meteorological influence via temperature, humidity, solar radiation, and wind speed.
We find that the SAI scenario does a comparably good job of cooling global average temperatures and heat indices, as SSP245. For example, in 2100, the temperature would be cooler than SSP585 by 3.1ºC in the SAI scenario, and 3.3°C in the decarbonization pathway.
However, the cooling is not projected to be uniform across global land regions. For example, the North American region would have stronger cooling benefits under SAI, while regions such as Australia would suffer more under SAI than decarbonization. Therefore, the global disparity of climate impacts are widened rather than reduced.
More importantly, the heat relief when quantified using ESI and AT indices shows even larger disparity enhancement, possibly due to an enhancement of the polar vortex in the Northern Hemisphere, which has been observed during previous large volcanic eruptions stemming from ozone depletion, stratospheric heating, and a decrease in temperature gradient. This impact has not been seen in the Southern Hemisphere, which can lead to disparities in the ability of SAI to evenly distribute cooling effects.
Citation
Muhlenforth, Lexi Rae (2023). Contrasting Stratospheric Aerosol Injection Geoengineering with Greenhouse Gas Emission Cuts in Mitigating Human Thermal Stress Globally. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /199940.