Sorry for the slow blogging, but with the AGU fun run starting at 6.15am, and the Awards ending at around ~10pm, and the actual science portion of the day squeezed in the middle, little time was available on Wednesday for reporting. Thursday seemed equally busy. So today you get two days in one.
One session on Wednesday that was really quite good was the session on Earth System Sensitivity. We’ve discussed this before (notably in discussing Hansen’s Target CO2 paper). The main idea is that the sensitivity of the climate system to a radiative forcing is not going to be constrained to effect only the factors included in GCM in 1979. That is, other feedbacks come into play – vegetation, ice sheets, aerosols, CH4 etc. will all change as a function a warming (or cooling), which are not included in the standard climate sensitivity definition. Talks by Eelco Rohling, Dan Lunt, and Jim Hansen all made excellent points on how one should think about constraints on ESS from paleo-climate records. The periods considered were mainly the Pleistocene ice age cycles, the LGM and the Pliocene, but Paul Valdes provided some interesting modeling that also included the Oligocene, the Turonian, the Maastrichtian and Eocene, indicating the importance of the base continental configuration, ice sheet position, and ocean circulation for sensitivity. Vegetation feedbacks were invariably reported as an amplifying feedback – which is interesting because that encompasses both ‘fast’ and ‘slow’ feedbacks.
Wednesday night was the awards, and as we reported, one of us (Gavin) was presented with the inaugural prize for Climate Communication. He will be posting a specific piece on this honor in a couple of days.
Thursday, there was a keynote (video available here) from Ben Santer at the Stephen Schneider event who persuasively argued that in doing the science necessary to refute baseless claims made in the media and in front of Congress, actual progress can be made beyond simply demonstrating that the original claim was made up. Specifically, he addressed a claim made by Will Happer, a Princeton professor, that no models demonstrate decadal variability in trends (which was not the case), and explored in depth the signal to noise ratio in determining climate trends much more comprehensively than had been done previously.
In sessions, there were a lot of papers on new approaches to estimating the climate of the common era (since 0 AD) – many of them using Bayesian methods of one sort or another. Hugues Goosse gave an interesting talk on paleo-data assimilation. A poster session had some first results from the CMIP5 models – including some intriguing results from Ben Booth looking at the Hadley Centre simulations of the role of aerosols in forcing multi-decadal variability in the North Atlantic.