The U.S. House Committee on Science and Technology has held a series of hearings over the past year on climate geoengineering. The recent testimony of Dr. Philip Rasch of the Pacific Northwest National Laboratory would be a very good class reading for a geoengineering module because it explores a number of important issues, including the potential cost of such schemes, the contours of research and deployment, potential time lags in impacts, and a good explanation of the mechanisms of the two primary solar radiation management, stratospheric sulfate aerosol and tropospheric cloud seeding.
Among the key take-aways in the testimony:
- Relevant activities for geoengineering research include assessment and evaluation of potential strategies, computer modeling, , labor and field works, technology development and deployment;
- Even prior to deployment, any nation engaging in a geoengineering program would require “enormous activity,” comparable in scope to the Intergovernmental Panel on Climate Change’s modeling and assessing activities, the Manhattan Project, or both;
- A rough estimate of the cost of full deployment of a stratospheric sulfur dioxide aerosol scheme would be a few billion dollars; expenditure of $10-50 million annually would have “an enormous effect” on research activities;
- While we would have “strong hints” as to whether stratospheric sulfate aerosols were effective within a couple of years of deployment, scientists would be more comfortable with such an assessment in 5-10 years; it also would take multiple years to sort out both the positive and potential negative implications of deployment (negative implications could include regional declines in precipitation, depletion of the ozone layer);
- There would be substantial difficulties in evaluating sulfur dioxide aerosol injection schemes without full deployment; for example introducing aerosol over a small patch of Earth would result in rapid dilution, and thus we wouldn’t expect the aerosols to dilute in the same way as with more extensive deployment;
- If society were to deploy a cloud seeding scheme to enhance cloud albedo, noticeable temperature impacts would occur within a couple of years, but it would also take a number of years to assess potential negative consequences, e.g. changes in major precipitation systems.