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Researcher Finds Greenland Melt Accelerating
12 December 2007
The 2007 melt extent on the Greenland ice sheet broke the 2005 summer melt record by 10%, making it the largest ever recorded there since satellite measurements began in 1979, according to a University of Colorado at Boulder climate scientist.
The melting increased by about 30% for the western part of Greenland from 1979 to 2006, with record melt years in 1987, 1991, 1998, 2002, 2005 and 2007, said CU-Boulder Professor Konrad Steffen, director of the Cooperative Institute for Research in Environmental Sciences. Air temperatures on the Greenland ice sheet have increased by about 7° F since 1991, primarily a result of the build-up of greenhouse gases in Earth’s atmosphere, according to scientists.
Steffen gave a presentation on his research at the fall meeting of the American Geophysical Union held in San Francisco from 10-14 December. His team used data from the Defense Meteorology Satellite Program’s Special Sensor Microwave Imager aboard several military and weather satellites to chart the area of melt, including rapid thinning and acceleration of ice into the ocean at Greenland’s margins.
Steffen maintains an extensive climate-monitoring network of 22 stations on the Greenland ice sheet known as the Greenland Climate Network, transmitting hourly data via satellites to CU-Boulder to study ice-sheet processes.
Although Greenland has been thickening at higher elevations due to increases in snowfall, the gain is more than offset by an accelerating mass loss, primarily from rapidly thinning and accelerating outlet glaciers, Steffen said.
The amount of ice lost by Greenland over the last year is the equivalent of two times all the ice in the Alps, or a layer of water more than one-half mile deep covering Washington, D.C.
—Konrad Steffen
The Jacobshavn Glacier on the west coast of the ice sheet, a major Greenland outlet glacier draining roughly 8% of the ice sheet, has sped up nearly twofold in the last decade, he said. Nearby glaciers showed an increase in flow velocities of up to 50 percent during the summer melt period as a result of melt water draining to the ice-sheet bed, he said.
The more lubrication there is under the ice, the faster that ice moves to the coast. Those glaciers with floating ice 'tongues' also will increase in iceberg production.
—Konrad Steffen
Greenland is about one-fourth the size of the United States, and about 80% of its surface area is covered by the massive ice sheet. Greenland hosts about one-twentieth of the world’s ice—the equivalent of about 21 feet of global sea rise. The current contribution of Greenland ice melt to global sea levels is about 0.5 millimeters annually.
The most sensitive regions for future, rapid change in Greenland’s ice volume are dynamic outlet glaciers like Jacobshavn, which has a deep channel reaching far inland, Steffen said.
Inclusion of the dynamic processes of these glaciers in models will likely demonstrate that the 2007 Intergovernmental Panel on Climate Change assessment underestimated sea-level projections for the end of the 21st century.
—Konrad Steffen
Helicopter surveys indicate there has been an increase in cylindrical, vertical shafts in Greenland’s ice known as moulins, which drain melt water from surface ponds down to bedrock, he said. Moulins, which resemble huge tunnels in the ice and may run vertically for several hundred feet, switch back and forth from vertical to horizontal as they descend toward the bottom of the ice sheet.
Steffen and his team have been using a rotating laser and a sophisticated digital camera and high-definition camera system provided by NASA’s Jet Propulsion Laboratory to map the volume and geometry of moulins on the Greenland ice sheet to a depth of more than 1,500 feet.
We know the number of moulins is increasing. The bigger question is how much water is reaching the bed of the ice sheet, and how quickly it gets there.
—Konrad Steffen
Steffen said the ice loss trend in Greenland is somewhat similar to the trend of Arctic sea ice in recent decades. In October, CU-Boulder’s National Snow and Ice Data Center reported the 2007 Arctic sea-ice extent had plummeted to the lowest levels since satellite measurements began in 1979 and was 39% below the long-term average tracked from 1979 to 2007.
CIRES is a joint institute of CU-Boulder and the National Oceanic and Atmospheric Administration.
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December 12, 2007 in Climate Change | Permalink | Comments (30) | TrackBack (0)
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Posted by: Andrey | December 16, 2007 at 01:09 AM
Andrey, thanks much. That looks like a lot of graphic data in one place. Jrojai also helped by pointing me in a direction that let me find the Met graphic (also shown on JunkScience) from the Hadley Centre:
http://www.metoffice.gov.uk/research/hadleycentre/CR_data/Monthly/upper_air_temps.gif
It appears, from the graphics, that claims that new global temperature records are being set since 1998 must mean that 1998 is discounted as an anomaly due to the extreme "El Nino" condition that year. Also, it may be that reports that the temperatures have been "flat" since 1999 are based on keeping 1998 and maybe keeping a "moving average" over the last so many (10?) years.
Aym, the reduction in "surface area" can not be equated to a reduction in total volume; the coastal glaciers and snow cover are a lot thinner than the inland ice pack. Cutting the head off a nail in a piece of wood greatly reduces the surface area of the metal but doesn't have nearly the effect on the volume of the metal that it appears to from overhead observation. And, concerning how local the MWP was, "Ice core data from Wyoming (Naftz et al., 1994) and Peru (Aber, 2000) also supports a global warm period consistent with the MWP and a global cool period consistent with the LIA.":
http://www2.sunysuffolk.edu/mandias/lia/determining_climate_record.html
Jrojai, thanks for your help. Peer review is an ongoing process that often takes a few years It was the IPCC that promoted Mann's "hockey stick" graphic from 1991 to 2005 and has since dropped it. An overlay of Mann's and Moberg's results can be seen here:
http://www.answers.com/topic/ipcc7-1-mann-moberg-png
Peer review still improves IPCC it would seem, since comparing their 2007 report has lowered estimates for sea level and temperature rise: 35 inches (2001) vs 17 inches (2007) and 2.52 to 10.4 F (2001) vs 3.24 and 7.24 F (2007).
I haven't made a New Year's Resolution in too long to remember, but when I get back from vacation, I'm going to make one to get a lot deeper into this climate science stuff.
Have a Merry Christmas and a Happy New Year.
Posted by: Arthur | December 16, 2007 at 05:28 AM
Global warming theory does explain/model the the effect on Greenland. The increased moisture creates more snow. The transformation of snow to neve to firn to ice can take decades. It's not just volume, it's total mass of ice. The modeling I read put the increase in the centre as a temporary phenomenon, which would be overtaken by erosion. And that was a over a year ago. The thinning and breaking up in part is being explained as melt water lubricating the glacial movement.
I've seen the site you've given. It does not invalidate my response to the criticisms of stan and his view that it was a skewed study that emphasized that the data was picked from one side on Greenland when the picture obviously showed an overall erosion on all sides.
http://www.realclimate.org/index.php/archives/2006/03/greenland-ice-and-other-glaciers/
Admittedly, there was some sort MW anomaly. The extent of it, both in terms of time and geography vary extensively. Very little data for Australia, for example. In another case, there is a huge bit of ice that recently broke off of the Ayles ice shelf that was 3000 to 4000 years old. If the MWP matched and exceeded today's temperatures for such an extended period in the area, there wouldn't be such geological features. They would've be eroded away during the period. Obviously, during the MWP, the conditions didn't match todays.
http://news.bbc.co.uk/1/hi/sci/tech/6218333.stm
http://en.wikipedia.org/wiki/Medieval_warm_period
Junk Science was and is a front end for Steve Milloy, long time tobacco, drug and oil industry lobbyist, and who has been a reliable source for what I considered junk for years. Known to have taken oil and tobacco money and recently kicked out of the Cato Institute, I would rather go to a fortune cookie for enlightenment. He produces spin and that's about it. If you think his position is so great invest in his Free Enterprise Action Fund.
http://www.sourcewatch.org/index.php?title=Steve_Milloy
http://en.wikipedia.org/wiki/Steve_Milloy
Posted by: aym | December 16, 2007 at 08:56 AM
Aym,
I don’t think that it’s necessarily a given about the Ayles Ice Sheet since Ellesmere ice has been breaking up and going away for 12,000 years:
http://www.abc.net.au/news/newsitems/200612/s1819606.htm
The sea level was 300 feet lower during the last ice age than it is now; so the Ellesmere Island ice that became the Ellesmere Ice Shelf was much more grounded and much thicker at that time. The process of its breakup and recycling into an interglacial pattern has been going on since the rising interglacial sea level picked it up and put it afloat.
So, my reasoning is that the Ayles Ice Shelf was called a 3000-4500 year old feature because ice cores of it return 3000-4500 years of snowfall evidence. Since Arctic sea ice typically melts from currents in the water beneath it, ice that was under what became the Ayles Ice Sheet when the breakup started 12,000 years ago (around the beginning of the current interglacial) has been eroding away from the bottom and evidence of snowfall from the last Ice Age up to 4500 years ago is gone.
So, yes, I would expect that a “4500 year old” feature would survive through both the MHWP and the MWP because it is made up of snow that was deposited more recently on top of a much older and thicker feature that was grounded 500 miles from the North Pole during the last Ice Age and has been disappearing ever since.
If I’m reasoning above my head here, please remember Plato’s advice, "Be kind, for everyone you meet is fighting a hard battle" and, "Never discourage anyone who continually makes progress; no matter how slow."
Posted by: Arthur | January 06, 2008 at 11:56 AM
Well I guess the question is should teh average individual be afraid? Are we taking a water level catastrophe in 2050?
Posted by: Holly | March 15, 2008 at 08:55 AM
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Arthur:
In convenient graphic form OFFICIAL (sources provided) temperature time series from both satellite measurements systems (UAH and RSU) and from weather stations reconstructions (very unreliable and much criticized), with regional and Hemispherical divisions are presented here:
http://www.junkscience.com/MSU_Temps/Warming_Look.html
Note that for all satellite measurement period from 1979 North Polar Region was warming, and South Polar Region was cooling.
In graphic form data for all US weather stations (you can find nearest to your home) is presented here:
http://www.co2science.org/scripts/CO2ScienceB2C/data/ushcn/ushcn.jsp