Posted by admin on Tuesday, January 15 @ 18:50:46 CET
Anonymous writes "
Rignot, a professor of earth system science at University of California, Irvine, is also a senior scientist with NASA's Jet Propulsion Laboratory.
A transcript follows.
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Marc Kaufman: Good morning, and thanks for joining us. We also are fortunate to have Eric Rignot, author of the Nature study on Antarctica, on the chat, and he and I will do our best to answer your questions. Eric has studied Antarctica and Greenland for 15 years and is well known for his research. Before we start, a brief correction from me: Mt. Kilimanjaro is not, as I wrote, in Kenya, but in Tanzania.
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Clarksville, Md.: The article today referenced Western Antarctica as on land, but also below sea level. Could you please explain this?
Eric Rignot: West Antarctica ice is grounded below sea level. But the top of the ice sheet is of course above sea level. Think about a vast expanse of ice sitting in the middle of the sea and reaching all the way down to the sea floor.
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Clarksville, Md.: Using the best scientific common sense with data to date, what is the acceleration trend for the melting that you understand to be happening in Antarctica, and how does that translate into sea level rise by year or decade?
Eric Rignot: The actual trend in Antarctica is a contribution to sea level rise that increased from about 0.3 mm/yr in 1996 to 0.5 mm/yr in 2006. It was certainly lower prior to 1996, and will continue to increase in years to come.
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Jefferson, N.C.: Sirs:
I have not seen Dr. Rignot's paper in NATURE, so my question may have already been answered.
For several years, there has been an indication that the temperatures over the Antarctic have cooled, as seen in the satellite data provided by MSU instruments as analyzed by UAH. This same data set was also analyzed by RSS and they chose to exclude any results poleward of 70S because of contamination due to the high elevations of interior Antarctica. Other researchers have reported that there is a warming trend seen in data collected near the coasts of Antarctica. In a paper published in the GRL, I found an apparent flaw in a comparison between sonde data and that produced by the UAH team (2003GL017938), perhaps another indication of surface contamination.
My question is, does the data in the NATURE paper support the claim that the Antarctic is warming and if so, how might that finding be reconciled with the cooling trend found by John Christy et al. at UAH?
R. E. Swanson
Eric Rignot: Good point. Antarctica's interior is cooling. The only air warming is in the Peninsula. But we are seeing at present in the glaciers is not related to atmospheric forcing. We think it is related to thermal forcing from the ocean. Changes in tropospheric circulation and wind patterns have enabled warm sources of water to reach glacier grounding lines and melt them from the bottom. This was the trigger for glacier acceleration in a large section of Antarctica.Melting of the frontal sections reduces the backforce on the glaciers and allows them to flow faster, much like what would happen if you slowly uncork a wine bottle .. or water bottle ..
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Bowdoinham, Maine: If the western shelf is largely below sea level, please explain how melting could contribute to sea level rise.
Eric Rignot: The portion of West Antarctica which is below will contribute little to sea level change if it melts in the ocean; only the portion that is sitting above sea level will contribute in full. There is enough ice sitting above sea level however to raise total sea level by 5-6 m if West Antarctica were to melt to sea
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Camden, Maine: It seems to me that the experts have consistently (almost) been too conservative in their estimates of coming changes in ice melt and other climatic changes.
Here's my question: Can't they somehow get the bigger picture and therefore predict with more accuracy? There are tons of inputs from all over the planet and taken collectively it would seem that even I, a simple lay person, can project that the future is going to be very, very exciting and challenging. I sometimes get the sense that the scientists are trying to downplay the obvious so as not to be too overbearing. Many did that in pre-Katrina times and look where it got us. I'd prefer to hear the unvarnished truth and have time to adjust and deal with it.
I'm working under the current assumption that climate change is going to be H-U-G-E and dealing with it is going where no man has gone before. Your thoughts?
Thanks.
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