"Greenland . . . is a sideshow in the sea level question."
I see nothing in the Dahl-Jensen article that could possible justify such a sweeping and dismissive claim. Alley himself says: "We have high confidence that warming will shrink Greenland, by enough to matter a lot to coastal planners." 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 <http://dotearth.blogs.nytimes.com/2009/02/06/richard-alleys-orbital-and-cli mate-dance/> Richard Alley, who's become a vital touchstone for me on such research, for some insights. Here's 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 kids' 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 Greenland's ice than Antarctica's, and we have greater confidence that Greenland will be "well-behaved" - we will more easily project changes in Greenland's 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) [ <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> link] 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 ( <http://dotearth.blogs.nytimes.com/2008/07/03/a-tempered-view-of-greenlands- gushing-drainpipes/> moulins, for example) - drama that focused my attention for a few years too - is a sideshow in the sea level question. That's not how it's been cast. There's been talk of <http://iopscience.iop.org/1755-1315/6/45/452009/pdf/1755-1315_6_45_452009.p df> regional geo-engineering to "save" the ice sheet. The <http://www.washingtonpost.com/blogs/capital-weather-gang/post/greenland-ice -sheet-surface-melt-huge-deal-or-overblown/2012/07/25/gJQAlfcT9W_blog.html> dramatic surface melting, 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 Greenland's 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 <http://www.nature.com/ngeo/journal/v4/n8/box/ngeo1194_BX1.html> Ian Joughin's and my [West Antarctic Ice Sheet] review in 2011, 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 <http://www.journals.elsevier.com/quaternary-science-reviews/> 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 <http://www.youtube.com/watch?feature=player_embedded&v=o4oMsfa_30Q&noredire ct=1> Youtube 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- climate-disaster-of-all/ -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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