cc: Keith Briffa , Tim Osborn , Bo Vinther date: Wed, 7 Nov 2007 11:48:07 +0000 from: Thomas Kleinen subject: Re: Query on Arctic sea ice to: Nathan Gillett Hi Nathan. I guess I best answer this one directly. Bo Vinther had approached us with the observation that sulphate aerosol emissions in North America and Europe had decreased a lot stronger than the projections in the SRES scenarios assume, and he had speculated that this might be one of the reasons for the rapid sea ice decline in the Arctic (less aerosol cooling). So I did two quick runs, one with SRES CO2 and sulphate, and one with sulphate decreasing a lot quicker. I looked at both annual and September sea ice coverage, and the difference between the two runs is not significant in any way. What Keith is referring to is the fact that even under the normal SRES scenarios sea ice in HadCM3 is disappearing rather quickly already - starting from an already very low sea ice coverage. The attached plot shows September sea ice cover in the arctic, blue is SRES B2, red is changed aerosol. So HadCM3 already has a strong decrease in sea ice for the late 20th century, which would imply a nearly ice-free Arctic in the 2050 timeframe, if the trend continues. The values for 2007 are actually pretty close to observed sea ice coverage (4-and-a-bit 10^12 m^2), but the 20th century sea ice cover was underestimated by nearly 25%, and therefore reduction is not as strong as in the real world. The second figure is from the Stroeve et al. GRL 2007, showing this for all IPCC models and observations (2007 still missing). Here HadCM3 is the very lowest... Cheers, Thomas On Wednesday 07 November 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 [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 > > > > http://www.cru.uea.ac.uk/cru/people/briffa/ Attachment Converted: "c:\documents and settings\tim osborn\my documents\eudora\attach\icearea_sep2.eps" Attachment Converted: "c:\documents and settings\tim osborn\my documents\eudora\attach\stroeve.jpg"