Xavier, A., Bala, G., Roose, S., & Kh, U. (2024). An investigation of the relationship between tropical monsoon precipitation changes and stratospheric sulfate aerosol optical depth. Oxford Open Climate Change, 4(1), kgae016.
Abstract
Stratospheric aerosol geoengineering (SAG) is one of the several solar geoengineering options that have been proposed to counteract climate change. In the case of SAG, reflective aerosols injected into the stratosphere would reflect more sunlight and cool the planet. When assessing the potential efficacy and risks of SAG, the sensitivity of tropical monsoon precipitation changes should be also considered. Using a climate model, we perform several stylized simulations with different meridional distributions and amounts of volcanic sulfate aerosols in the stratosphere. Because tropical monsoon precipitation responds to global mean and interhemispheric difference in radiative forcing or temperature, we quantify the sensitivity of tropical monsoon precipitation to SAG in terms of two parameters: global mean aerosol optical depth (GMAOD) and interhemispheric AOD difference (IHAODD). For instance, we find that the simulated northern hemisphere monsoon precipitation has a sensitivity of −1.33 ± 0.95% per 0.1 increase in GMAOD and −7.62 ± 0.27% per 0.1 increase in IHAODD. Our estimated precipitation changes in terms of the two sensitivity parameters for the global mean precipitation and for the indices of tropical, northern hemisphere, southern hemisphere and Indian summer monsoon precipitation are in good agreement with the model simulated precipitation changes. Similar sensitivity estimates are also made for unit changes in global mean and interhemispheric differences in effective radiative forcing and surface temperature. Our study based on planetary energetics provides a simpler framework for understanding the tropical monsoon precipitation response to external forcing agents.
"Live recording of Oliver Morton (The Economist) talk at Cornell University, as part of the 14th GeoMIP workshop.
Carl Sagan and Jim Pollack wrote together in 1993: "Clearly more work is needed, but comparatively inexpensive and environmentally prudent methods of mitigating greenhouse warming on Earth may be within reach in the next few decades." Sagan always thought
about planetary climates as things which could be engineered, with papers on terraforming Mars and Venus in the 1960s and 1970s; it is a way of thinking which can be traced back to that of Arrhenius and the other early comparative planetologists of the late 19th/early 20th century. Applying it in a straightforward way to the Earth is problematic in ways Sagan may well not have appreciated. But what he wrote with Pollack thirty years ago was arguably true then and seems true now. What are we to make of the possibility?"
