Hi Andy‹Your agreement with the dismissive statement on Greenland seems terribly short-sighted. Over the coming decade (if not already), we¹ll be setting a course for Greenland that will lead to much higher sea level in the future (and the contributions from Greenland and Antarctica will end up being far more than from thermal expansion and melting glaciers). A key issue at present among politicians is the impacts we are imposing on future generations (national debt, etc.)--well, dealing with Greenland melting is quite the predicament we would be posing to future generations (so the children and grandchildren of today¹s politicians).
Mike On 1/28/13 9:56 AM, "Andy Revkin" <[email protected]> wrote: > A sideshow to sea-level questions on policy-relevant time scales. (2100-ish at > best).. > > You're talking geological scale here. > > Tad Pfeffer's 2008 analysis of worst-case discharge rate still a keystone to > clear thinking on this. > > > On Mon, Jan 28, 2013 at 2:38 PM, Thomas Homer-Dixon <[email protected]> > wrote: >> ³Greenland . . . is a sideshow in the sea level question.² >> >> I see nothing in the Dahl-Jensen article that could possible justify such a >> sweeping and dismissive claim. Alley himself says: ³We have high confidence >> that warming will shrink Greenland, by enough to matter a lot to coastal >> planners.² >> >> Thomas Homer-Dixon >> University of Waterloo >> >> >> >> >> On Jan 28, 2013 5:12 PM, "Andrew Revkin" <[email protected]> wrote: >> There's also fresh input from Richard A. (and Waleed Abdalati) on Greenland >> and sea level in this new dot earth post: >> >> >> >> Eyes Turn to Antarctica as Study Shows Greenland's Ice Has Endured Warmer >> Climates http://nyti.ms/Yq7uhA >> >> >> >> I turned to Richard Alley >> <http://dotearth.blogs.nytimes.com/2009/02/06/richard-alleys-orbital-and-clim >> ate-dance/> , who¹s become a vital touchstone for me on such research, for >> some insights. Here¹s his comment, followed by my closing thoughts: >>> I have three immediate responses: Satisfaction in the great success of the >>> collaboration, concern that this slightly increases worries about future >>> sea-level rise from human-caused warming, but technical questions that may >>> leave us more-or-less where we were before on the biggest picture. >>> Taken in turn: >>> Having watched colleagues go to the immense effort of learning what >>> information is desired by policymakers and other citizens, assemble the >>> logistical and scientific abilities to supply that information, and actually >>> do it over a lot of years, and knowing just how many of their kids¹ soccer >>> games and recitals some of the scientist-parents missed, I have to smile >>> when the team succeeds so well. >>> As to the big picture, there is strong evidence from the history of sea >>> level on coasts from the Eemian that both Greenland and Antarctic ice sheets >>> shrank notably, contributing to a globally averaged sea-level rise of very >>> roughly 20 feet. This occurred primarily in response to a rearrangement of >>> where sunshine reached the planet and when during the year, with more summer >>> sunshine in the north but very little total change. And, some uncertainty >>> has remained on the exact balance between Greenland and Antarctic >>> contributions. The new paper suggests that the contribution from Greenland >>> was on the low end of the prior estimates, but has little effect on the >>> estimated total sea-level change, which points to a larger Antarctic source >>> than the previous best estimate. >>> In my opinion (and I believe the opinions of many colleagues), we have >>> greater understanding of Greenland¹s ice than Antarctica¹s, and we have >>> greater confidence that Greenland will be ³well-behaved² ‹ we will more >>> easily project changes in Greenland¹s ice, with greater confidence that >>> changes begun now will take centuries or longer to be mostly completed. >>> By shifting more of the sea-level rise into the less-understood ice, and >>> thus into the ice with greater chance of doing something rapidly, I believe >>> the new paper at least slightly increases the concerns for coastal planners, >>> even if the chance of a rapid change from Antarctic ice remains small. >>> As to the technical parts, as described in many sources, we have lots of >>> paleothermometers for the central Greenland ice cores over the last 100,000 >>> years, providing multiple validation and high confidence that temperatures >>> have been estimated accurately. The very changes in the ice sheet that are >>> of greatest interest here also make the effort quite difficult. The melting >>> of the Eemian interferes with gas-based paleothermometry, and with the >>> total-gas technique that provides constraints on changes in surface >>> elevation. >>> A U.S. government CCSP report on Arctic paleoclimates a few years ago (to >>> which I contributed) [link >>> <http://dotearth.blogs.nytimes.com/2013/01/24/eyes-turn-to-antarctica-as-stu >>> dy-shows-greenlands-ice-has-endured-warmer-climates/%3Ehttp:/www.climatescie >>> nce.gov/Library/sap/sap1-2/final-report/default.htm> ] estimated changes in >>> temperature and ice volume for this interval. The new estimates overlap with >>> the older ones. Were I working on that report now, I would recommend >>> expanding the uncertainties a little to include the new results. However, >>> considering that ice shrinkage on Greenland has a feedback effect (exposing >>> rocks allows more sun to be absorbed, causing more warming), considering the >>> evidence of Eemian warmth from marine records around Greenland, considering >>> climate model runs for that time, considering other studies of Greenland, >>> and recalling the notable uncertainties associated with untangling the >>> changes in total gas and in the ice sheet itself, I suspect that the >>> estimates in that CCSP report will stand up pretty well, with the new work >>> primarily confirming the prior understanding of climate changes and >>> ice-sheet and sea-level response in the Eemian. >>> If anyone is thinking that this paper means we can crank up the temperature >>> without worrying about sea level, they should seriously re-think. Overall, a >>> great and successful scientific effort leaves us with the knowledge that >>> warming does tend to melt ice, and that contributes to sea-level rise. >> In a followup note to him, I said: >>> Beautifully articulated. but I do think [the new work] closes the case that >>> Greenland, despite all of its drama (moulins, for example >>> <http://dotearth.blogs.nytimes.com/2008/07/03/a-tempered-view-of-greenlands- >>> gushing-drainpipes/> ) ‹ drama that focused my attention for a few years too >>> ‹ is a sideshow in the sea level question. >>> That¹s not how it¹s been cast. There¹s been talk of regional geo-engineering >>> to ³save² the ice sheet >>> <http://iopscience.iop.org/1755-1315/6/45/452009/pdf/1755-1315_6_45_452009.p >>> df> . The dramatic surface melting >>> <http://www.washingtonpost.com/blogs/capital-weather-gang/post/greenland-ice >>> -sheet-surface-melt-huge-deal-or-overblown/2012/07/25/gJQAlfcT9W_blog.html> >>> , while important to track and understand (as is being done by Jason Box and >>> others) has little policy significance. >> Alley replied: >>> I do think it has been clear for a while that interactions with the ocean >>> provide the greatest potential for surprises and rapid changes, and that >>> Greenland¹s ice sheet would mostly pull out of the ocean before it lost most >>> of its mass. The discussion in the attached, as well as in Ian Joughin¹s and >>> my [West Antarctic Ice Sheet] review in 2011 >>> <http://www.nature.com/ngeo/journal/v4/n8/box/ngeo1194_BX1.html> , were >>> pointing in that direction. The lack of huge danger from the lake drainages >>> probably was argued (possibly for the first time) by Byron Parizek and I >>> in Quaternary Science Reviews >>> <http://www.journals.elsevier.com/quaternary-science-reviews/> in 2004. >>> There are dynamics issues, but the biggest ones go away once shrinkage pulls >>> the ice out of the ocean. Then, a serious focused research effort should be >>> able to produce (and indeed, is producing) quantified projections with >>> useful uncertainties that can be narrowed by continuing effort on the >>> established research path. We are still thinking about one or two >>> interesting and possibly surprising things, but Greenland looks like it is >>> mostly the known-unknown ice sheet. >>> >>> >> >> >> >> On Mon, Jan 28, 2013 at 11:56 AM, David Lewis <[email protected]> >> wrote: >> Richard Alley discussed the potential Greenland and Antarctic contribution to >> sea level rise in a talk at Stanford in late October 2012 which is available >> on Youtube >> <http://www.youtube.com/watch?feature=player_embedded&v=o4oMsfa_30Q&noredirec >> t=1> >> >> On Monday, January 28, 2013 2:45:00 AM UTC-8, Oliver Tickell wrote: >> http://grist.org/climate-energy/why-greenlands-melting-could-be-the-biggest-c >> limate-disaster-of-all/ -- 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]. 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