Exploring the Climate Impacts of Solar Geoengineering on Land-Atmosphere Interactions

Abstract

We are already on our way to a much warmer world. As humans continue to emit greenhouse gases into the atmosphere, avoiding the worst increases in surface temperature will likely require climate mitigation or even climate intervention. Solar geoengineering refers to a set of proposed methods to mitigate climate changes from greenhouse warming by manipulating the incoming solar radiation. To fully understand the consequences of solar geoengineering, research is needed to examine the impacts it will have on the climate system and understand how those impacts compare to the climate changes induced by a warming world. This thesis explores the climate impacts of solar geoengineering in a modeling context, focusing in particular on land-atmosphere coupling, terrestrial water cycling, regional climate variability, and vegetation-climate interactions. Modeling studies have demonstrated the potential of solar geoengineering to compensate temperature increases from climate change. We examine changes in the terrestrial hydrologic cycle under global model simulations of solar geoengineering and increased greenhouse gas forcing. The interactions between vegetation water cycling and climate drive global and regional changes when uniform solar reductions are used to compensate elevated carbon dioxide (CO2) levels. We expand our modeling framework to utilize multiple large ensembles of simulations to examine how climate variability is impacted by solar geoengineering on a regional scale. Summer heat extremes decrease under solar geoengineering relative to a high-CO2 climate, and in some cases extremes decrease relative to present-day climate. The coupling between soil moisture and daily maximum temperature is identified as a key mechanism in driving the variability response. We explore the sensitivity of land surface model parameters using a state-of- the-art land surface model. We identify the parameters which soil moisture and evapotranspiration are most sensitive to, based on possible ranges of values from the literature. Our results provide a foundation for understanding and interpreting the land surface feedbacks and mechanisms identified by the solar geoengineering modeling studies in this thesis. We return to a global coupled modeling framework and examine impacts on terrestrial ecosystems under solar geoengineering designed to hold anthropogenic radiative forcing fixed, relative to a mid-range future emissions scenario. Although potential changes in biodiversity are not completely avoided, the outlook for conservation improves under solar geoengineering relative to a warming climate.