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Extreme Melting on Greenland Ice Sheet, Reports CCNY Team
Posted on 31 October 2011 by John Hartz
Glacial Melt Cycle Could Become Self-Amplifying, Making it Difficult to Halt
The Greenland ice sheet can experience extreme melting even when temperatures don’t hit record highs, according to a new analysis by Dr. Marco Tedesco, assistant professor in the Department of Earth and Atmospheric Sciences at The City College of New York. His findings suggest that glaciers could undergo a self-amplifying cycle of melting and warming that would be difficult to halt.
Marco Tedesco standing on the edge of one of four moulins (drainage holes) he and his team found at the bottom of a supraglacial lake during the expedition to Greenland in the summer, 2011. (Credit: P. Alexander)
(click thumbnail for larger-size image)
“We are finding that even if you don’t have record-breaking highs, as long as warm temperatures persist you can get record-breaking melting because of positive feedback mechanisms,” said Professor Tedesco, who directs CCNY’s Cryospheric Processes Laboratory and also serves on CUNY Graduate Center doctoral faculty.
Professor Tedesco and his team collected data for the analysis this past summer during a four-week expedition to the Jakobshavn Isbræ glacier in western Greenland. Their arrival preceded the onset of the melt season.
Combining data gathered on the ground with microwave satellite recordings and the output from a model of the ice sheet, he and graduate student Patrick Alexander found a near-record loss of snow and ice this year. The extensive melting continued even without last year’s record highs.
The team recorded data on air temperatures, wind speed, exposed ice and its movement, the emergence of streams and lakes of melt water on the surface, and the water’s eventual draining away beneath the glacier. This lost melt water can accelerate the ice sheet’s slide toward the sea where it calves new icebergs. Eventually, melt water reaches the ocean, contributing to the rising sea levels associated with long-term climate change.
The model showed that melting between June and August was well above the average for 1979 to 2010. In fact, melting in 2011 was the third most extensive since 1979, lagging behind only 2010 and 2007. The “mass balance”, or amount of snow gained minus the snow and ice that melted away, ended up tying last year’s record values.
Temperatures and an albedo feedback mechanism accounted for the record losses, Professor Tedesco explained. “Albedo” describes the amount of solar energy absorbed by the surface (e.g. snow, slush, or patches of exposed ice). A white blanket of snow reflects much of the sun’s energy and thus has a high albedo. Bare ice – being darker and absorbing more light and energy – has a lower albedo.
But absorbing more energy from the sun also means that darker patches warm up faster, just like the blacktop of a road in the summer. The more they warm, the faster they melt.
And a year that follows one with record high temperatures can have more dark ice just below the surface, ready to warm and melt as soon as temperatures begin to rise. This also explains why more ice sheet melting can occur even though temperatures did not break records.
Professor Tedesco likens the melting process to a speeding steam locomotive. Higher temperatures act like coal shoveled into the boiler, increasing the pace of melting. In this scenario, “lower albedo is a downhill slope,” he says. The darker surfaces collect more heat. In this situation, even without more coal shoveled into the boiler, as a train heads downhill, it gains speed. In other words, melting accelerates.
Only new falling snow puts the brakes on the process, covering the darker ice in a reflective blanket, Professor Tedesco says. The model showed that this year’s snowfall couldn’t compensate for melting in previous years. “The process never slowed down as much as it had in the past,” he explained. “The brakes engaged only every now and again.”
The team’s observations indicate that the process was not limited to the glacier they visited; it is a large-scale effect. “It’s a sign that not only do albedo and other variables play a role in acceleration of melting, but that this acceleration is happening in many places all over Greenland,” he cautioned. “We are currently trying to understand if this is a trend or will become one. This will help us to improve models projecting future melting scenarios and predict how they might evolve.”
Additional expedition team members included Christine Foreman of Montana State University, and Ian Willis and Alison Banwell of the Scott Polar Research Institute, Cambridge, UK.
Professor Tedesco and his team provide their preliminary results on the Cryospheric Processes Laboratory webpage. They will will be presenting further results at the American Geophysical Union Society (AGU) meeting in San Francisco on December 5 at 9 a.m. and December 6 at 11:35 a.m.
The research was supported by the National Science Foundation and the NASA Cryosphere Program. The World Wildlife Fund is acknowledged for supporting fieldwork activities.
On the Internet:
2011 Melting in Greenland report
http://greenland2011.cryocity.org
Cryospheric Processes Laboratory
http://cryocity.org/
Professor Tedesco Tracks Life and Death of Greenland Glacial Lake
http://www1.ccny.cuny.edu/advancement/news/Tedesco-Greenland-Glacial-Lake.cfm
Map of expedition location
http://tinyurl.com/66h67so
Expedition Facebook page
http://www.facebook.com/pages/Cryocity/124269854300408
Expedition Twitter Feed
http://twitter.com/#!/Cryocity
Marco Tedesco profile
http://www1.ccny.cuny.edu/prospective/gsoe/ese/directory/profile-record.cfm?customel_datapageid_1237265=1252241
[DB] "It's my hope that SkS will help to remedy this lack of public information"
Science and scientists have been researching climate change and publishing that reaseach for more than a century. There have been active calls by scientists and scientific bodies for the public and media to pay more attention to their findings for many decades (which is why, for example, President Nixon established the EPA). So it is not for a lack of transparency, will and effort to reach the public that the message is not being delivered. So hints at conspiracy on the part of science are vastly misplaced.
That leaves the issue squarely in the laps of the media and the well-publicized and well-funded efforts of the anti-science community to block any efforts which may result in a declining usage of fossil fuels. And that is far beyond the realm of this post. It is my hope that any individuals willing to pursue this line of dialogue take it to a more appropriate thread (many exist), as it is off-topic here.
It was not my intention to imply any conspiracy on the part of science in my comment above. I wrote specifically of 'steering' by political, not scientific interests. The lack of quantified trends of the six mega-feedbacks' acceleration to date being - a/ assembled and b/ translated into language and graphic form accessible to the public, is something I'd be delighted to find I was wrong on. Can anyone locate such information ? I wrote the comment here of SkS precisely because of its fine and consistent coverage of the feedback reports since its launch. But as far as I know, SkS has yet to publish those quantified trends-thus-far, as an assembly, in a form accessible to the layman. Thus I was hoping that there might be sufficient concern over the issue to consider a fresh suggestion. I still hope that I wasn't wrong on that. For those who choose to respond defensively and see no reason to raise the game, I suggest they try talking to ordinary people about the NOAA/NSIDC report on permafrost carbon emissions: "Permafrost melting will cause around 100 billion tonnes of carbon to be emitted by 2100, getting to about 500 million tonnes by 2020 and to 1,600 million tonnes in 2100, - but that doesn't account for the CO2-equivalent warming due to part of the carbon coming out as methane, which is 72 times as potent as a greenhouse gas as carbon dioxide, - and it doesn't include extra melting due to the warming caused by the permafrost greenhouse gas emissions; - or that due to the several other interactive mega-feedbacks that are now accelerating; - or that due to the foreseeable loss of the cooling sulphate pollution that ending our fossil fuel emissions will curtail." An ordinary person hearing such a litany of unquantified hazards is more likely to be turned off than concerned. The need for the clearest quantified overview achievable is thus very real - not for the minority who are still duped by fossil interests, but for the far larger numbers who accept AGW and see the need of action, but are not remotely well-enough informed of the scale and urgency of threat to demand action with implacable determination. Those who want to carry on tussling with deniers to chip away at their minority support are in my view entirely laudable in their efforts, but addressing the majority with information that can generate the demand for action is evidently the necessary precursor to action being achieved at the earliest possible date. I would hope that we can at least agree that achieving commensurate action on climate is our common goal.Regards, Lewis[DB] Lewis, it is with the greatest of regret that I intervene here. Not becuase of what you write isn't of interest or not needing further exploration; both are. But because it is off-topic to this thread.
With that in mind, I invite you to write this up as a guest post for consideration for publication here at SkS. If you are interested, just respond to this here and I will email you the details.
Again, if others want to explore portions of this on some of the other, more pertinent threads, feel free to do so & leave a pointer stub here. Thanks!