Collaborative Research in Evaluation of Suggestions to Geoengineer the Climate System Using Stratospheric Aerosols and Sun Shading

Principal Investigators: Alan Robock and Richard P. Turco
Co-Principal Investigators: Georgiy Stenchikov, Martin Bunzl

Project Summary
In response to the global warming problem, there has been a recent renewed call for geoengineering “solutions” involving injecting anthropogenic aerosols into the stratosphere. While simple calculations have shown that sulfate aerosols would cool the planet on a global average basis, both tropical and high-latitude volcanic eruptions also produce large regional climate changes in temperature and precipitation. Furthermore, aerosols injected into the stratosphere move with atmospheric winds and interact with the climate system to change that very circulation. In addition, aerosols, whether formed from gases or injected as aerosols, evolve in the atmosphere both chemically and physically. Taking advantage of our experience with modeling the climate response to volcanic eruptions, we propose to simulate the climate response to various suggested geoengineering schemes, including injecting aerosols or precursors into the tropical stratosphere or polluting just the Arctic stratosphere. As part of the evaluation, we will calculate how the particle size distributions and optical properties vary in time due to interactions with each other and chemical interactions with gases, and impacts of those changes on radiative heating and atmospheric circulation. We will calculate the climate response to the changing aerosols and radiatively important gases as a function of the location and timing of injections. We will calculate the transformation, transport, and removal of the aerosols and impacts on the surface, including acid precipitation. We will also consider schemes to block solar radiation outside the atmosphere. This work will consider a range of scenarios and produce a systematic evaluation of both the efficacy and potential consequences of proposed geoengineering schemes. In addition, we will explicitly address the ethics and policy implications of such schemes.