Predicting the Effects of Targeted Spectral Band Attenuation in Solar Geoengineering

Abstract:

Solar geoengineering could alleviate the impact of climate change. However, solar geoengineering cannot exactly offset the effects of CO2. For example, previous modeling results have suggested that it is not possible to restore both global average temperature and precipitation rates at the same time. The reason is that, per unit of forcing, stratospheric aerosols and CO2 have different effects on the atmospheric energy budget, and therefore on precipitation. However, previous modeling results have focused on solar geoengineering methods that reduce solar insolation roughly uniformly across the solar spectrum. Here we investigate the potential effects of solar geoengineering which attenuates only certain bands of the solar spectrum. This band-specific approach provides a greater level of control for balancing radiative energy fluxes at different heights throughout the atmosphere, allowing a closer match between the effects of solar geoengineering and CO2 on the atmospheric energy budget. As a proof-of-principal, we first demonstrate that the band-specific approach can simultaneously restore temperature and precipitation to their unperturbed values in idealized cloud-resolving simulations of radiative-convective equilibrium. Next, we use the Community Earth System Model (CESM) to investigate the effects of targeted spectral band attenuation on the atmosphere’s energy budget in a comprehensive global simulation. The results of this study test the proposition that spectral band attenuation could simultaneously return both the total radiative energy budget and the precipitation levels back towards those of the pre-industrial era. The latter outcome is potentially a major advantage over that of applying the more commonly proposed method of dimming the full spectrum of solar radiation.