Last week in Science two researchers reported on the Greenland ice sheet, which is melting about twice as fast as expected ten years ago. American’s leading climatologist, James Hansen, wrote in the UK’s Independent (archived here) about what this means for us in the temperate zone:
Today’s forecasts of sea-level rise use climate models of the [Greenland] ice sheets that say they can only disintegrate over a thousand years or more. But we can now see that the models are almost worthless. They treat the ice sheets like a single block of ice that will slowly melt. But what is happening is much more dynamic.
Once the ice starts to melt at the surface, it forms lakes that empty down crevasses to the bottom of the ice. You get rivers of water underneath the ice. And the ice slides towards the ocean.
Dr. Jeff Masters Wunderblog discusses the issue in depth, and makes the same point as Hansen:
The most worrying aspect of the paper’s findings is that we are told that the computer models used to estimate how long it will take Greenland’s ice will melt are significantly in error–and in the wrong direction!
Exxon/FOXNews hack Stephen Milloy eagerly agrees with "Calamity Jim" that circulation models:
are not the tools for the [predictive] job and we have little prospect of developing such tools in the foreseeable future.
But he waves off the idea that the melting of the Greenland ice sheet could be a problem, declaring:
Gosh Jim, there’s a lot of noise here but seems precious little substance…
In his post, which is highly recommended, Masters discusses the same "noise" of conflicting studies as Milloy mentions, but he’s significantly less reassured:
However, the doubling in glacier flow observed in the past ten years comes as a major shock. The models used to come up with the 1000 year estimate do not account for changes in glacier speed at all! The unexpected increase in glacier flow probably occurred in response to the lubrication effect of melt-water penetrating down to the glacial bed, as well as other poorly-understood processes. The paper concluded: "Current models used to project the contribution to sea level from the Greenland Ice Sheet in a changing climate do not include such physical processes and hence do not account for the effect of glacier dynamics." In other words, the models were wrong. Climate change skeptics are find of criticizing computer models, and cite their inadequacy as grounds for dismissing the threat of climate change. Well, it works both ways. Climate change models can be off in the wrong direction–as we also saw with the Antarctic ozone hole, which was completely missed by the models. These new results imply that if Greenland warms significantly (at least 3° degrees C), Greenland’s ice could melt in a few centuries, not 1000 years. With 20 feet of sea level rise locked up in its ice, sea level rises well beyond the capability of humans to handle could occur later this century.
Kit Stolz 