Effects of Solar Geoengineering on Indian Monsoon Precipitation Patterns

Abstract

The unlikelihood of staying below the Paris Climate goal of 1.5-2°C has led some to more seriously consider geoengineering to cool the planet as we continue cutting emissions. Injecting sulfate aerosols into the stratosphere cools the planet, mimicking volcanic eruptions, however, it is likely to alter global precipitation patterns. Few studies have been done on more regional scales to examine these changes in precipitation. This thesis investigates the precipitation changes in the Indian summer monsoon under four scenarios: double-CO2, 1% reduction in solar radiation (offsets half of global warming), a northern hemisphere volcanic eruption, and a southern hemisphere eruption.

It is found that -1% solar radiation reduces Indian monsoon rainfall in a similar spatial pattern as double-CO2 increases rainfall, implying solar geoengineering might moderate, rather than exacerbate precipitation changes in India. The asymmetric, volcanic eruptions lead to more complex spatial variations in precipitation changes, with some parts of India increasing in precipitation, while others decrease. It is also found that the Agung (SH) eruption leads to fractional precipitation changes of comparable magnitude to the double-CO2 and -1% solar radiation experiments, indicating an uneven deployment of aerosols could be just as impactful as a doubling of CO¬2¬. The mechanisms of these precipitation changes are partially explained by changes in moist static stability, energy convergence, and specific humidity, but leave large residuals, indicating other mechanisms like horizontal advection, eddies, and the subtropical jet stream may also be important in diagnosing the causes of precipitation changes associated with global warming and solar geoengineering.