Ethon brings word of April Fool's Jokes Boulder style

It's pretty hard to keep the irony meter on scale these days. The National Anonymice Academy had no sooner taken up the issue of ice cap rot, when Steve Bloom scurried in from Austin Texas, with news from the parallel meeting of the Western Antarctic Links to Sea Level Estimation (WALSE) Workshop. This proves the power of convening a meeting of the Anonymice Academy for focusing attention on important matters. Word had also run to our friends in Boulder who, if they were the long eared types would be complimented on the wonderful knots they are tying in their ears.

Eli thought it would be a good thing to contrast and compare some of the text from the Hansen Arxiv paper the Academy has been studying, with the consensus statement that emerged from the WALSE group, who presumably had a number of expert glaciologists sitting in.

• Satellite observations show that both the grounded ice sheet and the floating ice shelves of the Amundsen Sea Embayment have thinned over the last decades.

Hansen: The most compelling data for the net change of ice sheets is provided by the gravity satellite mission GRACE, which shows that both Greenland (Chen et al 2006) and Antarctica (Velicogna et al 2006) are losing mass at substantial rates. The most recent analyses of the satellite data (S. Klosco et al priv. comm.) confirm that Greenland and Antarctica are each losing mass at a rate of about 150 cubic kilometers per year, with the Antarctic mass loss primarily in West Antarctica. These rates of mass loss are at least a doubling of rates of several years earlier, and only a decade earlier these ice sheets were much closer to mass balance (Casenave 2006)....

Warming ocean waters are now thinning some West Antarctic ice shelves by several meters per year (Payne et al 2004; Shepherd et al 2004).

• Ongoing thinning in the grounded ice sheet is already contributing to sea-level rise.

Hansen: Under BAU forcing in the 21st century, sea level rise undoubtedly will be dominated by a third term (3) ice sheet disintegration. This third term was small until the past few years, but it is has at least doubled in the past decade and is now close to 1 mm/year, based on gravity satellite measurements discussed above.

• The thinning of the ice has occurred because melting beneath the ice shelves has increased, reducing the friction holding back the grounded ice sheet and causing faster flow.

Hansen: Acceleration of ice sheet disintegration requires tapping into ocean heat, which occurs primarily in two ways (Hansen 2005): (1) increased velocity of outlet glaciers (flowing in rock-walled channels) ice streams (bordered mainly by slower moving ice), and thus increased flux and subsequent melting of icebergs discharged to the open ocean, and (2) direct contact of ocean and ice sheet (underneath and against fringing ice shelves). Ice loss from the second process has a positive feedback on the first process: as buttressing ice shelves melt, ice stream velocity increases.

• Oceanic changes have caused the increased ice-shelf melting. The observed average warming of the global ocean has not yet notably affected the waters reaching the base of the ice shelves. However, recent changes in winds around Antarctica caused by human influence and/or natural variability may be changing ocean currents, moving warmer waters under the ice shelves.

Hansen: Modeling studies yield increased ocean heat uptake around West Antarctica and Greenland due to increasing human-made greenhouse gases (Hansen et al 2006b). Observations show a warming ocean around West Antarctica (Shepherd et al 2004), ice shelves thinning several meters per year (Rignot and Jacobs 2002; Payne et al 2004), and increased iceberg discharge (Thomas et al 2004).

• Our understanding of ice-sheet flow suggests the possibility that too much melting beneath ice shelves will lead to “runaway” thinning of the grounded ice sheet. Current understanding is too limited to know whether, when, or how rapidly this might happen, but discussions at the meeting included the possibility of several feet of sea-level rise over a few centuries from changes in this region.

Hansen: Positive feedback from loss of buttressing ice shelves is relevant to some Greenland ice streams, but the West Antarctic ice sheet, which rests on bedrock well below sea level (Thomas et al 2004), will be affected much more. Loss of ice shelves provides exit routes with reduced resistance for ice from further inland, as suggested by Mercer (1978) and earlier by Hughes (1972). ...

An important point is that the non-linear response could easily run out of control, because of
positive feedbacks and system inertias.......The nonlinearity of the ice sheet problem makes it impossible to accurately predict sea level change on a specific date.

We leave it as a challenge to find Hansen's opinion on the remaining issues. A good place to start is his slippery slope argument in Climate Change, which, among other things points to problems with ice sheet models.

• The experts agreed that to reduce the very large uncertainties concerning the behavior of the Antarctic ice in the Amundsen Sea Embayment will require new satellite, ground, and ship-based observations coupled to improved models of the ice-ocean-atmosphere system. Issues include:

1. The recent changes were discovered by satellite observations; however, continued monitoring of some of these changes is not possible because of a loss of capability in current and funded satellite missions.
2. The remoteness of this part of Antarctica from existing stations continues to limit the availability of ground observations essential to predicting the future of the ice sheet.
3. No oceanographic observations exist beneath the ice shelves, and other oceanographic sampling is too infrequent and sparse to constrain critical processes.
4. Current continental-scale ice sheet models are inadequate for predicting future sea level rise because they omit important physical processes.
5. Current global climate models do not provide information essential for predicting ice sheet and oceanic changes in the Amundsen Sea Embayment; for example, ice shelves are not included.

However, Eli would appreciate some furry rodent to explain the contradiction that lunch claims in his April Fools joke:

2. There is the "possibility of several feet of sea-level rise over a few centuries from changes in this region." This contrasts strongly with Jim Hansen's assertion that

"Spatial and temporal fluctuations are normal, short-term expectations for Greenland glaciers are different from long-term expectations for West Antarctica. Integration via the gravity satellite measurements puts individual glacier fluctuations in proper perspective. The broader picture gives strong indication that ice sheets will, and are already beginning to, respond in a nonlinear fashion to global warming.There is enough information now, in my opinion, to make it a near certainty that IPCC BAU climate forcing scenarios would lead to disastrous multi-meter sea level rise on the century time scale"

unless someone out there thinks that several feet is substantially different from multi-meter or that a large sea level rise over 1-3 centuries would be a walk in the park. Living a mile or so up may give one a sense of security we at sea level lack. OTOH, there is less O2 up high.