A new study on probably the leading climate geoengineering scheme, stratospheric sulfur dioxide injection, has been published in the journal Atmospheric, Chemistry and Physics Discussions, Jones, et al., Geoengineering by Stratospheric SO2 Injection: Results From the Met Office HadGEM2 Climate Model and Comparison with the Goddard Institute for Space Studies ModelE, 10 Atmos. Chem. Phys. Discuss. 7421-7434 (2010) (open access). The study compares the results of two models to simulate geoengineering by continuous injection of sulfur dioxide, the Met Office Hadley Centre’s HadGEM2-AO climate model and the Goddard Institute for Space Studies ModelE. The article is written well and would be approachable for graduate students in a climate policy course, as well as law students; it is also a good case study to emphasize several important themes in the context of climate geoengineering, including large abiding uncertainties about effectiveness, a good discussion about some of the potential downsides of sulfur injection, and suggestions for a future research agenda.
Among the key take-aways from the study:
- Both models revealed dramatic cooling in the first decade of injection of 5 teragrams of sulfur dioxide per year, 0.74K for the Hadley model, and 0.47K for the Goddard model; both models show approximately a -0.7K drop in temperatures in the second decade relative to corresponding A1B scenarios. The authors do caution that this assumes instantaneous full activation of the scheme, as opposed to a more incremental approach;
- The strongest cooling in both models occurs in higher norther latitudes, and cooling is generally stronger over land than oceans in both models;
- After about 30 years, global-mean near-surface temperatures under the Hadley simulation are about the same as at the start of the simulation, meaning that any further global warming due to increasing atmospheric concentrations of GHGs could be avoided.
- However, there would be regional variability. For example, the models project some land areas in central Africa and Australia would be up to 1K cooler than during the period of 1990-1999, whereas the Amazon region would be warmer by a similar amount. Most strikingly, the polar amplification of temperatures due to ice-albedo feedbacks would result in an overwhelming of the cooling effect of geoengineering at these latitudes;
- The models do not agree on regional precipitation changes associated with sulfur dioxide injection in some cases with the Goddard model showing a reduction in the eastern USA, whereas the Hadley model shows a increase. On the other hand, both models agree that tropical precipitation maxima over the Atlantic and much of the Pacific oceans would be displaced southwards, resulting in precipitation reductions in sub-Saharan Africa and land areas around the Bay of Bengal (at least vis-a-vis a A1B scenario v. current conditions);’
- The Hadley model suggests that sulfur dioxide injection would defer a given amount of warming under the A1B scenario by 30-35 years, though rapid warming would occur if geoengineering wasn’t maintained;
- Future research should focus on further assessment of geoengineering models, ideally using common experiment designs, before any serious consideration of potential deployment of the scheme could be considered.
Some of the discussion questions that might be used in association with this study include:
1. Does the “Sword of Damocles” that sulfur dioxide geoengineering might engender, i.e. the need to maintain injections lest very rapid warming occur after cessation, argue against such a scheme?;
2. Why do regional variations occur in terms of warming and precipitation? What are the equitable concerns associated with these variations, and how would a system of governance address these issues?
3. What other potential negative impacts of sulfur dioxide injection could you envision?