Poster's note - One argument for geoengineering readiness is the risk of a climate runaway. The classic runaway case is that of Venus, which goes 'to infinity and beyond' (Lightyear, 1995). Hansen, as I recall, has argued that this is feasible on earth as a result of AGW. The model run below suggests otherwise. However, I can't see any evidence that methane feedback was considered, which may provide sufficient additional radiative forcing. Nevertheless, a sensitivity of 8C at any point on the curve suggests we have some serious trouble ahead if they've underestimated sensitivity at lower CO2 levels.
Fast Atmosphere–ocean Model Runs with Large Changes in CO2 - Russell - GRL - Wiley http://onlinelibrary.wiley.com/doi/10.1002/2013GL056755/abstract How does climate sensitivity vary with the magnitude of climate forcing? This question was investigated with the use of a modified coupled atmosphere–ocean model, whose stability was improved so that the model would accommodate large radiative forcings, yet be fast enough to reach rapid equilibrium. Experiments were performed in which atmospheric CO2 was multiplied by powers of two, from 1/64 to 256 times the 1950 value. From 8 to 32 times the 1950 CO2, climate sensitivity for doubling CO2 reaches 8 °C due to increases in water vapor absorption and cloud top height, and to reductions in low level cloud cover. As CO2 amount increases further, sensitivity drops as cloud cover and planetary albedo stabilize. No water vapor induced runaway greenhouse caused by increased CO2 was found for the range of CO2examined. With CO2 at or below 1/8 of the 1950 value, runaway sea ice does occur as the planet cascades to a snowball Earth climate with fully ice covered oceans and global mean surface temperatures near – 30 °C. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/groups/opt_out.
