In response to the global warming problem, there has been a recent renewed call for geoengineering “solutions” involving injecting particles into the stratosphere or blocking sunlight with satellites between the Sun and Earth. Here we describe different proposed geoengineering designs, and then show climate model calculations with the coupled atmosphere-ocean NASA GISS ModelE GCM that evaluate both their efficacy and their possible adverse consequences. We conduct experiments by simulating global warming with and without continuous emissions of sulfate aerosol precursors both into the tropical lower stratosphere and into the high latitude Northern Hemisphere lower stratosphere. We find that while stratospheric aerosols can cool the planet on a global average basis with tropical emissions or cool the Northern Hemisphere with high latitude emissions, there are also large regional climate changes in temperature and precipitation, with large areas of drought.

At the current level of understanding, there are too many potential problems with geoengineering, and it would be much cheaper and easier to solve the global warming problem by reducing greenhouse gas emissions. These problems will be described, and include cost, continued ocean acidification, obtaining global agreement on the optimum climate, regional climate changes, ozone depletion, reduction of solar energy for power generation, and unexpected consequences.