Abstract
Stratospheric aerosol injection (SAI) is considered as a backup approach to mitigate global warming, and understanding its climate impact is of great societal concern. It remains unclear how differently global monsoon (GM) precipitation would change in response to tropical and Arctic SAI. Using the Community Earth System Model, a control experiment and a suite of 140-year experiments with CO2 increasing by 1% per year (1% CO2) are conducted, including ten tropical SAI and ten Arctic SAI experiments with different injecting intensity ranging from 10 to 100 Tg yr−1. For the same amount of injection, a larger reduction in global temperature occurs under tropical SAI compared with Arctic SAI. The simulated result in the last 40 years shows that, for a 10 Tg yr−1 injection, GM precipitation decreases by 1.1% (relative to the 1% CO2 experiment) under Arctic SAI, which is weaker than under tropical SAI (1.9%). Further, tropical SAI suppresses precipitation globally, but Arctic SAI reduces the Northern Hemisphere monsoon (NHM) precipitation by 2.3% and increases the Southern Hemisphere monsoon (SHM) precipitation by 0.7%. Under the effect of tropical SAI, the reduced GM precipitation is mainly due to the thermodynamic term associated with the tropical cooling-induced decreased moisture content. The hemispheric antisymmetric impact of Arctic SAI arises from the dynamic term related to anomalous moisture convergence influenced by the anomalous meridional temperature gradient.
Highlights
Global monsoon (GM) precipitation has been viewed as the dominant mode of annual variation in the tropical region, which imposes substantial impacts on the society and living environment of two-thirds of the world’s people (Wang and Ding 2008; Wang et al 2012)
We use Community Earth System Model (CESM) to analyze the impacts of tropical and Arctic Stratospheric aerosol injection (SAI) on GM precipitation changes compared to a 140-yr experiment with C O2 increasing by 1% every year (1% CO2)
We find that an increased global mean temperature occurs during 101–140 in the tropical SAI experiments with intensity less than or equal to 40 Tg yr−1, while a decreased global temperature only occurs in the
Summary
Global monsoon (GM) precipitation has been viewed as the dominant mode of annual variation in the tropical region, which imposes substantial impacts on the society and living environment of two-thirds of the world’s people (Wang and Ding 2008; Wang et al 2012). Nalam et al (2018) found that Arctic geoengineering shifts the ITCZ southward and causes the precipitation decrease (increase) over the Northern (Southern) Hemisphere monsoon regions using the Community Atmosphere Model version 4 (CAM4) coupled to a slab ocean model These studies use the different injection intensities for the tropical/global and Arctic SAI experiments, which is hard to reflect the contribution of tropical and Arctic SAI to the climate changes. Recent studies using the CESM1-CAM5 and proxy data found a weakened (strengthened) Northern (Southern) Hemisphere monsoon following northern eruptions (Fasullo et al 2019; Meng et al 2019) They suggested that the dynamic process associated with atmospheric circulation change plays an essential role in precipitation response.
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