cc: t.kleinen@uea.ac.uk date: Wed Nov 7 11:54:55 2007 from: Keith Briffa subject: Re: Query on Arctic sea ice to: Nathan Gillett Hi Nathan We used only the Hadley Centre model .We were looking at sea ice extent, in the expectation that with more rapidly reducing circum North Atlantic tropospheric aerosol inputs (as indicated by the latest estimates and the ice core concentrations) compared to the AR4 assumptions, we might expect more rapid local warming and faster ice melting than has previously been expected. We note that HadCM3 had the lowest ice extent of all the models anyway . We only looked at global mean temperature, which did not warm any faster with reduced aerosol input than before. The sea ice extent was not significantly different from the AR4 run. Thomas can show you these runs . He is still going to extract the spatial pattern of warming from this run (right Thomas?) but other than that we pretty much abandoned the idea of a quick paper indicating drastic immediate ice melt. The runs still indicate no permanent sea ice with 30-50 years which is still amazing - but not publishable. At 11:17 07/11/2007, you wrote: Hi Keith, This sounds interesting, and is new compared to other findings.. I was just at a workshop on polar climate change and I think Marika Holland reported that none of the IPCC models simulate single year decreases in summer minimum ice comparable to that observed this year in the Arctic (some of the models such as the NCAR model do show large interannual changes, but none as large as observed). Were you looking at changes in summer minimum ice, or in annual mean ice? And how were these runs different from e.g. the Hadley Centre's HadCM3 runs? Cheers, Nathan Keith Briffa wrote: Dear all this is best answered by Thomas Kleinen here , as he has just completed some runs with the unified model and lower tropospheric aerosols than were previously input in the recent 20th century - looking at the speed of sea ice melting and temperature change. The bottom line is that the model gets roughly correct melting (close to what we observe ) AND THE LIKELY IMPLICATIONS FOR FUTURE WARMING ARE "not significantly different than what we previously believed would happen". Keith At 09:14 05/11/2007, James Screen wrote: Hi I've been contacted by a Mr Mike Parr regarding the recent loss of Arctic sea ice and it's implications on sea-ice/climate modeling. See email below. I'm sure there is someone better placed than me to answer his query. Most of my studies have focused on Antarctica and I don't consider myself a sea-ice expert. If you think you can help Mr Parr please email him directly (info@pwr.co.uk). Cheers James -----Original Message----- From: Mike Parr [[1]mailto:info@pwr.co.uk] Sent: 04 November 2007 10:46 To: j.screen@uea.ac.uk Subject: Arctic Ice loss Dear Mr Screen, I picked up your name from the CRU web site - forgive me for writing direct but I have a question which you may not be able to answer directly perhaps you know one of your colleagues that could. I'm working with a couple of government agencies (European) on climate change (isn't everybody these days). One of the issues I would like to clear up is, given the recent and surprising loss of arctic summer sea ice how current models may change. If I look at Hadley centre data on this subject (which they seem to obtain from CRU??) it seems somewhat out of kilter with what is actually happening. I was wondering if (and how) models might be modified in light of this year's developments? I would also be interested in the link between arctic summer sea ice loss and if anybody is giving some thought to how a changing arctic ocean albedo might impact on ice outflows from Greenland (one could - not unreasonably - imagine an acceleration in such outflows given an albedo for sea ice of 0.6 to 0.8 and that for water of 0.05?). Any help would be most appreciated, best regards, Mike Parr. -- Professor Keith Briffa, Climatic Research Unit University of East Anglia Norwich, NR4 7TJ, U.K. Phone: +44-1603-593909 Fax: +44-1603-507784 [2]http://www.cru.uea.ac.uk/cru/people/briffa/ -- **************************************************************************** Dr. Nathan Gillett, Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK. Tel: +44 (0) 1603 593 647 Fax: +44 (0) 1603 507 784 Email: n.gillett@uea.ac.uk [3]http://www.cru.uea.ac.uk/~nathan/ **************************************************************************** -- Professor Keith Briffa, Climatic Research Unit University of East Anglia Norwich, NR4 7TJ, U.K. Phone: +44-1603-593909 Fax: +44-1603-507784 [4]http://www.cru.uea.ac.uk/cru/people/briffa/