August 7, 2010
By Andrew C. Revkin
Aug. 9, 8:30 a.m. | Updated An enormous iceberg, about four times the size of Manhattan, broke away from Greenland’s Petermann Glacier on Aug. 5.
Greenland has for years been shedding ice faster than the rate at which accumulating snow adds to the overall bulk of its ice sheet. The calving of an enormous ice “island” from the Petermann Glacier several days ago created a photogenic “moment” in a long-term process.
Jason E. Box, a glacier and climate researcher at Ohio State University who forwarded the image above (it was generated by the Canadian Ice Center), sent these reactions before heading into the field:
Petermann is a sleeping giant that is slowly awakening. Removing flow resistance leads to flow acceleration…. The coincidence of this area loss and a 30 square kilometer loss in 2008 with abnormal warmth this year, the setting of increasing sea surface temperatures and sea ice decline are all part of a climate warming pattern.
Questions about the eventual contribution to rising sea levels from Greenland’s eroding ice mass (and the West Antarctic Ice Sheet down south) remain hard to answer. I’ve put out a query to a batch of glaciologists for more thoughts and will update this post when they reply.
Aug. 9, 8:30 a.m. | Update
Andreas Muenchow of the University of Delaware is much more cautious than Ohio State’s Jason Box about attributing the ice breakup to recent warming. He submitted a comment below that I’m highlighting here:
Air temperatures have very little to do with this breakup because this glacier is losing more than 80% of its ice by melting from the ocean below this floating glacier. The newly broken off piece, as massive as it is, contributes less than 10% of the ice lost over 50 years. If one wants to make the connection to global warming for this glacier, one will need to proof that ocean temperatures under the ice have increased. And from measuring those for a day in 2003 and a day in 2006 and a day in 2007 and a day in 2009, we are barely able to provide a first description that we submitted for peer review a few weeks ago, e.g., http://muenchow.cms.udel.edu… … We are not even sure what the sill depth for this fjord is, e.g., the deepest part that connects Petermann Fjord with the rest of the ocean, within better than 100 meters. In much of the Arctic, temperature in the ocean increases with depth to about 300-500 meters which is the range of the likely sill depth. There is plenty of heat inside the fjord already to melt it from below (see linked manuscript), so an interesting question to ask (again, this may have nothing to do with climate change), why is the floating ice shelf there in the first place? Boundary layer physics, turbulence, tides, and glacier dynamics may all relate and may all be more fruitful ways in trying to understand what is happening than just to wave the hand and tick this off as another sign of global warming.
Global warming and climate change are very real and challenging problems, but it is foolish to assign every “visible” event to that catch-all phrase. It cheapens and discredits those findings where global warming is a real and immediate cause for observable phenomena. Details matter, in science as well as in policy.
I couldn’t agree more. It was important to note the development, as I did, but also to be careful about the lure of the “ front-page thought.”