I’m off to Italy for the next two weeks, starting tonight.
I suggested that the Erice seminar of the World Federation of Scientists have a session on Water Cycle Feedback, as this seemed to me to be the most important scientific issue affecting climate sensitivity. I had a couple of motives for suggesting this – first, it seemed to me to be the most important scientific issue involved in climate sensitivity; and second, I wanted to do something constructive for the seminar so that I would be invited back. It was a great visit last year and both my wife and I wanted to go again.
Fortunately, Zichichi and Manoli liked the suggestion and asked me to suggest terms and help with speakers. My description of the issue was:
The big question in climate is the “sensitivity” of global climate to doubled CO2. Estimates in AR4 GCMs vary from 2 to 4.5 deg C. Within the IPCC GCMs, the primary source of sensitivity uncertainty is cloud feedbacks, and, in particular, the shortwave response of low-level clouds (marine boundary layer). Despite a wide range of sensitivity within IPCC GCMs, IPCC GCMs do not necessarily span both sides of relevant characteristics of critical cloud types, e.g in tropical and midlatitude regions, simulations systemically yield clouds that are too optically thick, and not abundant enough in the mid-troposphere and in large-scale subsidence regimes.
- IPCC AR4 pinpointed the largest source of intermodel variability between IPCC models to SW response of low-level clouds. What are the prospects for narrowing this source of uncertainty?
- IPCC AR4 identified several areas of systemic bias in cloud modeling GCMs e.g in tropical and midlatitude regions by simulating clouds generally too optically thick, and not abundant enough in the mid-troposphere and in large-scale subsidence regimes. Do these (or other biases) result in any material risk of under- or over-estimation of climate sensitivity? How could this be tested?
- are cloud (and other GCM) properties sufficiently constrained to confidently exclude the possibility of either very high climate sensitivity (above 4.5 deg C) or low climate sensitivity (under 2 deg C)?
- if not, which modeling components (cloud or otherwise) are mostly likely to result in a large enough systemic bias to yield either a higher or lower climate sensitivity? What steps can be taken to reduce such areas of uncertainty?
- Can paleoclimate and/or other indirect studies add any confidence to constraining climate sensitivity?
I suggested a number of speakers on both sides of the debate. My own hope was that I’d be able to learn something from the debate. The roster has ended up being over-weighted towards “skeptic” speakers: Lindzen, Arking, Choi, Kininmonth, Paltridge, but it is a blue-ribbon “skeptic” session. Invited but unable to attend: Peter Webster, Judy Curry, Andrew Dessler, Stephen Schwartz, Sandrine Bony, Tom Crowley. The invitations were only made in May and schedules had unforunately filled in for many people by then. The final session is:
CLIMATE & CLOUDS
FOCUS: Sensitivity of Climate to Additional CO2 as indicated by Water Cycle Feedback Issues
Chairman A.Zichichi – Co-chair R. Lindzen
10.30 – 12.00
SESSION N° 9
* Dr. William Kininmonth
Australasian Climate Research, Melbourne, Australia
A Natural Constraint to Anthropogenic Global Warming
* Professor Albert Arking
Earth and Planetary Sciences Dept., John Hopkins University, Baltimore, USA
Effect of Sahara Dust on Vertical Transport of Moisture over the Tropical Atlantic and its Impact on Upper Tropospheric Moisture and Water Vapor Feedback.
* Dr. Yon-Sang Choi
Earth, Atmospheric and Planetary Sciences Dept., MIT, Cambridge, USA
Detailed Properties of Clouds and Aerosols obtained from Satellite Data
* Professor Richard S. Lindzen
Department of Earth, Atmospheric & Planetary Sciences, MIT, Cambridge
On the Determination of Climate Feedbacks from Satellite Data
* Professor Garth W. Paltridge
Australian National University and University of Tasmania, Hobart, Australia
Two Basic Problems of Simulating Climate Feedbacks
I’ll check in from time to time from Erice, but my blog attendance will be spotty. We’re going to be traveling in Italy for a few days on either side of the conference – in east Sicily around Siracusa for the next couple of days and Florence for a few days after the conference.
I’ve asked a few regulars to keep an eye on things while I’m away.