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: > “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 Richard > Alley<http://dotearth.blogs.nytimes.com/2009/02/06/richard-alleys-orbital-and-climate-dance/>, > 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) > [link<http://dotearth.blogs.nytimes.com/2013/01/24/eyes-turn-to-antarctica-as-study-shows-greenlands-ice-has-endured-warmer-climates/%3Ehttp:/www.climatescience.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.**** > > That’s not how it’s been cast. There’s been talk of regional > geo-engineering to “save” the ice > sheet<http://iopscience.iop.org/1755-1315/6/45/452009/pdf/1755-1315_6_45_452009.pdf>. > 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 > 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 Ian > Joughin’s 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&noredirect=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-climate-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]. > Visit this group at http://groups.google.com/group/geoengineering?hl=en. > For more options, visit https://groups.google.com/groups/opt_out. > > **** > > > > **** > > ** ** > > -- **** > > *_***** > > ** ** > > ANDREW C. REVKIN > Dot Earth blogger, The New York Times > http://www.nytimes.com/dotearth > Senior Fellow, Pace Acad. for Applied Env. Studies > Cell: 914-441-5556 Fax: 914-989-8009 > Twitter: @revkin Skype: Andrew.Revkin **** > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > Visit this group at http://groups.google.com/group/geoengineering?hl=en. > For more options, visit https://groups.google.com/groups/opt_out. > > **** > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > Visit this group at http://groups.google.com/group/geoengineering?hl=en. > For more options, visit https://groups.google.com/groups/opt_out. > > **** > -- *_* * * ANDREW C. REVKIN Dot Earth blogger, The New York Times http://www.nytimes.com/dotearth Senior Fellow, Pace Acad. for Applied Env. Studies Cell: 914-441-5556 Fax: 914-989-8009 Twitter: @revkin Skype: Andrew.Revkin -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
