Sunday, November 20, 2005

More on Global Warming

This is a follow-up to the post on that I posted earlier today.

Greg P prompted me to look into the issue a little more.  There is a comment thread at Huffington Post, but it is not very informative...or at least it wasn't until j7uy5 added a substantive comment earlier today.  I've expanded on that here.

Greg cited an article in Science (abstract) by Ola M. Johannessen et. al., that shows that the thickness of the ice cap is increasing, at least in the areas of greatest elevation.  The abstract, however, is not very informative.  The authors were interviewed by reporters, and some additional detail is available on CNN, here.  The CNN article includes information from some other scientists:
[...] And the scientists said that the thickening of the ice-cap might be offset by a melting of glaciers around the fringes of Greenland. [...]

"Ice sheets now appear to be contributing modestly to sea level rise because warming has increased mass loss from coastal areas more than warming has increased mass gain from enhanced snowfall in cold central regions," it said.

"Greenland presently makes the largest contribution to sea level rise," according to the report by scientists led by Richard Alley of Pennsylvania State University in the United States.
Similarly, the authors of the paper cited by The Independent have been interviewed elsewhere.  An interview published by TerraDaily, with the lead author, Ian Howat (a UCSC doctoral candidate in Earth Sciences), and his advisor, Slawek Tulaczyk, includes the following:
Satellite images dating back as far as the 1970s show that the front of the glacier has remained in the same place for decades.

But in 2001 it began retreating rapidly, moving back four and a half miles between 2001 and 2005. Howat's measurements also show that the Helheim glacier has sped up from around 70 feet per day to nearly 110 feet per day and thinned by more than 130 feet since 2001.

As the glacier speeds up and retreats, new factors come into play that cause further acceleration and retreat, Howat said. "This is a very fast glacier, and it's likely to get faster," he said. [...] "Outlet glaciers may have been thinning for over a decade," Howat said. "But it's only in the last few years that thinning reached a critical point and began drastically changing the glacier's dynamics. [...] "Our research provides strong evidence that rapid melting processes such as we observed at the Helheim glacier will play a role in ice sheet reduction, but they are currently not included in the models." Tulaczyk said.
Us non-geophysicists* can't really assess the science in all the papers written on the subject.  Even if we could, it would not be valid to cite just a few papers and pretend that we have a comprehensive understanding of the subject.  As perpetual sophomores, however, we are free to read a subset of the relevant literature and say what we think.  

The information here would indicate that the melting around the edges of the ice cap is more significant than the thickening of the top.  That certainly is what Howat, Tulaczyk and Alley believe.  Since they undoubtedly have already read the Johannessen paper, and have taken it into account, I tend to think they are correct.  However, we really need to wait until the Howat paper appears in print, and the experts have a chance to mull it over.  After all, that is how science works.  People publish their stuff, and everyone else tries to pick it apart.  If it survives, it becomes the latest version of the truth.
* Usage note: "non-geophysicist" sounds better than "non-earth scientist," and is not ambiguous.