Regional climate responses to geoengineering with tropical and Arctic SO₂ injections

Abstract

[1] Anthropogenic stratospheric aerosol production, so as to reduce solar insolation and cool Earth, has been suggested as an emergency response to geoengineer the planet in response to global warming. While volcanic eruptions have been suggested as innocuous examples of stratospheric aerosols cooling the planet, the volcano analog actually argues against geoengineering because of ozone depletion and regional hydrologic and temperature responses. To further investigate the climate response, here we simulate the climate response to both tropical and Arctic stratospheric injection of sulfate aerosol precursors using a comprehensive atmosphere-ocean general circulation model, the National Aeronautics and Space Administration Goddard Institute for Space Studies ModelE. We inject SO 2 and the model converts it to sulfate aerosols, transports the aerosols and removes them through dry and wet deposition, and calculates the climate response to the radiative forcing from the aerosols. We conduct simulations of future climate with the Intergovernmental Panel on Climate Change A1B business-as-usual scenario both with and without geoengineering and compare the results. We find that if there were a way to continuously inject SO 2 into the lower stratosphere, it would produce global cooling. Tropical SO 2 injection would produce sustained cooling over most of the world, with more cooling over continents. Arctic SO 2 injection would not just cool the Arctic. Both tropical and Arctic SO 2 injection would disrupt the Asian and African summer monsoons, reducing precipitation to the food supply for billions of people. These regional climate anomalies are but one of many reasons that argue against the implementation of this kind of geoengineering.

Modelling the size distribution of geoengineered stratospheric aerosols

“…In previous studies, it was assumed that geoengineered stratospheric aerosols would be smaller in size than their volcanic analogue (Crutzen, 2006, Robock et al, 2008Rasch et al, 2008). Our studies confirm findings of H09 that geoengineered stratospheric particles are likely to be larger than those observed in the stratosphere after large volcanic eruptions.…”

“…So far, only a few modelling studies addressed the global impact of geoengineered stratospheric aerosols by interactively treating the aerosol size (Rasch et al, 2008;Robock et al, 2008;Tilmes et al, 2009). However, in these studies, the aerosol size spectrum was not determined by aerosol microphysical processes.…”

Climate response to aerosol injection at different stratospheric locations

“…Equilibrium aerosol mass in the atmosphere (Figure 1) is achieved after approximately 2-3 years. It equals 3.6 Mt, therefore life time of aerosol is 0.9 years, that is not far from 12 months obtained by Robock et al (2008). Equilibrium temperature and precipitation response is reached 10-15 years from the beginning of injection.…”

A comparison of the climate impacts of geoengineering by stratospheric SO2 injection and by brightening of marine stratocumulus cloud

“…For geoengineering via stratospheric SO 2 injection, we use the simulations of Jones et al (2010) which follows Robock et al (2008) injecting 2.5 Tg [S] year −1 into the lower stratosphere (∼16-23 km). The standard version of HadGEM2 (model top at ∼40 km) is not a dedicated 'stratospheric' configuration, so to reduce any problems with stratospheric transport, SO 2 injection was applied uniformly across the globe.…”