-Arctic Ice

CO2 may have less of an effect on melting glaciers recently than previously thought. Solar energy is the major contributor, scientists now believe. Weather patterns this summer were what influenced how much of, and how fast, the sea ice the sun melted.

One result of these natural patterns was a decrease in cloud cover, scientists said at a meeting of the American Geophysical Union, which would have allowed more sunlight to penetrate Earth’s atmosphere and warm the Arctic ocean waters. This solar warming is felt to be more influential than trapped heat in the atmosphere as it affects  air, ice surface and water temperatures combined. An increase in air temperature alone would not have caused nearly as substantial a loss in sea ice coverage as was observed. In addition a warmer ambient temperature in the regional atmosphere would have increased the relative humidity and thus encouraged more cloud cover.

New data from NASA satellites observing the western Arctic, where most of the ice loss occurred, showed a 16-22 percent decrease in cloud coverage this summer compared to 2006.

"There were significant reductions in cloud cover this summer," said study member Graeme Stephens of Colorado State University.

The amount of sunlight from these clearer skies was enough to heat ocean waters by 4 degrees Fahrenheit (2.4 degrees Celsius), or enough to melt 1-1.5 feet (0.3+ meters) of sea ice, the scientists said.

"Clouds are conspiring, they’re playing the big role in this," said study author Jennifer Kay, a post-doctoral research fellow at the National Center for Atmospheric Research in Boulder, Colo.

Kay says the result of this work highlights the importance of the influence of weather pattern variability on the Arctic climate system.

"As Arctic sea ice thins, its extent is more sensitive to normal year-to-year variability in weather and cloud patterns," Kay said. "Our data show that clearer skies this summer allowed much more of the sun’s energy to melt the sea ice and heat the ocean surface."

-----------------------------------------------------------Greenland Ice

Scientists have discovered what they think may be a very significant reason why Greenland's ice is melting: a thin spot in Earth's crust is enabling underground magma to heat the ice.

They have found at least one enormous “hotspot” in the northeast corner of Greenland -- just below a site where an ice stream was recently discovered.

The researchers don't yet know how warm the hotspot is, but it is likely that it is warm enough to melt the ice above it and is lubricating the base of the ice sheet, enabling the ice to slide much more rapidly out to sea.

Ralph von Frese

“The behavior of the great ice sheets is an important barometer of global climate change,” said Ralph von Frese, leader of the project and a professor of earth sciences at Ohio State University. “However, to effectively separate and quantify any human impacts on climate change, we must understand the natural impacts, too.

“Crustal heat flow is still one of the unknowns -- and it's the significant one, according to our preliminary results. Greenland and Antarctica are both relatively active geothermal regions”

Timothy Leftwich, von Frese's former student and now a postdoctoral engineer at the Center for Remote Sensing of Ice Sheets at the University of Kansas, presented the study's early results on Thursday, December 13, 2007, at the American Geophysical Union meeting in San Francisco.

von Frese's team combined gravity measurements of the area taken by  Naval Research Laboratory aircraft with airborne radar measurements and NOAA satellite data recorded by research partners at the University of Kansas . The combined map revealed changes in mass beneath the Earth's crust, and the topography of the crust where it meets the ice sheet.

Below the crust is the mantle, the molten rock layer that surrounds the Earth's core. The crust varies in thickness, but is usually tens of miles thick. Even so, the mantle is so hot that temperatures just a few miles deep in the crust reach many hundreds of degrees Fahrenheit, von Frese explained.

“It could be that there's a vent (volcano) down there,” he said. “But we think it's probably the way the heat is being distributed by the rock topography under the base of the ice.”

“Where the crust is thicker, the base is cooler, and where it's thinner, it is, of course, warmer. And under a big place like Greenland or Antarctica , natural variations in the crust will make some parts of the ground beneath the ice sheet much warmer than others. As the ground grows warmer and ice thickness decreases, the sheets melt and migrate more rapidly.” he said.

The ice thickness, the temperature at the base of the ice, and ground topography all contribute to the forming of an ice stream -- a river of ice that flows within a larger ice sheet. In recent years, Greenland ice streams have been carrying ice out to sea faster, and ice cover on the island has been diminishing. Many scientists felt the melt rate was more than could have been attributed to any slight rise in ambient temperature, yet were unable to identify any specific causes for the increase. The discovery of the hot spot could explain the accelerated melt flow rate, which in turn carries larger volumes of ice seaward.

The ice sheet in northeast Greenland is especially worrisome to scientists. It had no known ice streams until 1991, when satellites spied one for the first time. Dubbed the Northeastern Greenland Ice Stream, it carries ice nearly 400 miles, from the deepest interior of the island out to the Greenland Sea.

“Ice streams have to have some reason for being there. And it's pretty surprising to suddenly see one in the middle of an ice sheet,” von Frese said. "Unless, it is melting from underneath..."

The newly discovered hotspot is just below the ice stream, and most likely caused it to form, the researchers concluded. But what caused the hotspot to form?

Collaborator Kees van der Veen began working on the project when he was a visiting associate professor of geological sciences and research scientist at Byrd Polar Research Center at Ohio State. He is now at the University of Kansas.

“Recent observations indicate that the Greenland Ice Sheet is much more active than we ever believed,” van der Veen said. “There have been rapid changes in outlet glaciers, for example. Such behavior is critically linked to conditions under the ice bed. Geothermal heat is the important factor, but until now, our models have not included spatial variations in heat, such as this hotspot. This is a relatively unstudied area as far as geothermal research is concerned, so most of our data regarding this subject is new. It had been assumed that the ice was melting faster due to greenhouse gas heat trapping, but we are finding out that is not likely the case."

“Our map is the very first attempt at quantifying spatial variations in geo-heat under Greenland -- and it explains why the Northeast Greenland Ice Stream is where it is,” van der Veen added.

To measure actual temperatures beneath the ice, scientists must drill boreholes down to the base of the ice sheet-- a mile or more below the ice surface. The effort, expense and lack of specific funding (most goes to CO2 research) make such measurements few and far between, especially in remote areas of northeast Greenland.

For now, the researchers are combining theories of how heat flows through the mantle and crust with the gravity and radar data, to understand how the hotspot is influencing the ice.

Once they finish searching the rest of Greenland for other hotspots, they hope to turn their attention to Antarctica.

This research was funded by the National Science Foundation.