Interesting Climate-Related Lecture..
So I just got back from a lecture hosted by MIT’s Department of Earth, Atmospheric and Planetary Sciences; Richard Alley (Pennsylvania State University) on “Fraying at the edges: ice sheets, climate and sea levels.”
Quite interesting. His context is basically that there is global warming, that models support the idea that it has both natural and human-induced contributions, that the warming so far is slight compared to what will come, and that it will continue, with some uncertainties as to rate, through at least about 2100.
He studies ice. (Actually, what he said was something very much like: “We do ice. We have more fun doing ice than you have doing whatever it is you do, and you should come and do ice with us.”) He is concerned with the melting of large ice sheets such as those over Greenland and Antarctica, and he basically had three points to make:
1. Movement of ice sheets may be more sensitive to warming than has been previously understood. As ice spreads and thins, it melts more quickly; the melt-water kind of lubricates it, and then it spreads and thins in an accelerating way. While it would take a long time for the ice sheets to melt in place, previous models have not taken into account the positive feedback that might act if their motion is enhanced.
2. They have found that the motion of ice sheets is actually strongly affected by conditions at the perimeters; the rising of the tide can slow the motion of a glacier at its face by a factor of 2, and the effect of the slow-down can be see up to 80 km inland. Where floating ice forms ice shelves at the margins of ice sheets, those ice shelves slow down the spreading of the ice upstream on the land.
3. These floating ice shelves seem to be much more sensitive to temperature changes than the ice sheets they border; they are in a warmer environment, being floating on the liquid seas, and therefore much closer to state change. The Larsen B ice shelf, off Antarctica, which was 220 meters thick, basically disintegrated over the course of a few weeks in early 2002.
The summarized predictions of the Intergovernmental Panel on Climate Change as of 2001 did not anticipate extensive ice loss from the major ice sheets as a result of the expected levels of global warming; increased snowfall was expected to make up for increased rate of melting. It would be easy to project from his remarks that he felt that this view was incorrect, and that slight changes in temperature could cause collapse of the ice shelves, leading to higher motion of the ice sheets, leading to more melting of them in turn, BUT Professor Alley was cautious to advise that his work raises more questions than it answers. Models based on the new observations and measurements are still in preliminary development, and not able to make any predictions useful for policy-making at this point.
I strongly recommend the Synthesis Report (Summary of Policymakers) of the “Third Assessment Report” of the International Panel on Climate Change (IPCC), available on line.
Quite interesting. His context is basically that there is global warming, that models support the idea that it has both natural and human-induced contributions, that the warming so far is slight compared to what will come, and that it will continue, with some uncertainties as to rate, through at least about 2100.
He studies ice. (Actually, what he said was something very much like: “We do ice. We have more fun doing ice than you have doing whatever it is you do, and you should come and do ice with us.”) He is concerned with the melting of large ice sheets such as those over Greenland and Antarctica, and he basically had three points to make:
1. Movement of ice sheets may be more sensitive to warming than has been previously understood. As ice spreads and thins, it melts more quickly; the melt-water kind of lubricates it, and then it spreads and thins in an accelerating way. While it would take a long time for the ice sheets to melt in place, previous models have not taken into account the positive feedback that might act if their motion is enhanced.
2. They have found that the motion of ice sheets is actually strongly affected by conditions at the perimeters; the rising of the tide can slow the motion of a glacier at its face by a factor of 2, and the effect of the slow-down can be see up to 80 km inland. Where floating ice forms ice shelves at the margins of ice sheets, those ice shelves slow down the spreading of the ice upstream on the land.
3. These floating ice shelves seem to be much more sensitive to temperature changes than the ice sheets they border; they are in a warmer environment, being floating on the liquid seas, and therefore much closer to state change. The Larsen B ice shelf, off Antarctica, which was 220 meters thick, basically disintegrated over the course of a few weeks in early 2002.
The summarized predictions of the Intergovernmental Panel on Climate Change as of 2001 did not anticipate extensive ice loss from the major ice sheets as a result of the expected levels of global warming; increased snowfall was expected to make up for increased rate of melting. It would be easy to project from his remarks that he felt that this view was incorrect, and that slight changes in temperature could cause collapse of the ice shelves, leading to higher motion of the ice sheets, leading to more melting of them in turn, BUT Professor Alley was cautious to advise that his work raises more questions than it answers. Models based on the new observations and measurements are still in preliminary development, and not able to make any predictions useful for policy-making at this point.
I strongly recommend the Synthesis Report (Summary of Policymakers) of the “Third Assessment Report” of the International Panel on Climate Change (IPCC), available on line.