The new study showed ice sheets like the Greenland Ice Sheet can respond to such warming on the order of decades rather than the centuries projected by conventional thermal models. Ice flows more readily as it warms, so a warming climate can increase ice flows on ice sheets much faster than previously thought, said the study authors.

“We are finding that once such water flow is initiated through a new section of ice sheet, it can warm rather significantly and quickly, sometimes in just 10 years, ” said lead author Thomas Phillips, a research scientist with Cooperative Institute for Research in Environmental Sciences. CIRES is a joint institute between CU-Boulder and the National Oceanic and Atmospheric Administration.

Phillips, along with CU-Boulder civil, environmental and architectural engineering Professor Harihar Rajaram and CIRES Director Konrad Steffen described their results in a paper published online in Geophysical Research Letters.

Conventional thermal models of ice sheets do not factor in the presence of water within the ice sheet as a warming agent, but instead use models that primarily consider ice-sheet heating by warmer air on the ice sheet surface. In water’s absence, ice warms slowly in response to the increased surface temperatures from climate change, often requiring centuries to millennia to happen.

But the Greenland ice sheet is not one solid, smooth mass of ice. As the ice flows towards the coast, grating on bedrock, crevasses and new fractures form in the upper 100 feet of the ice sheet. Melt water flowing through these openings can create “ice caves” and networks of “pipes” that can carry water through the ice and spreading warmth, the authors concluded.

To quantify the influence of melt water, the scientists modeled what would happen to the ice sheet temperature if water flowed through it for eight weeks every summer — about the length of the active melt season. The result was a significantly faster-than-expected increase in ice sheet warming, which could take place on the order of years to decades depending on the spacing of crevasses and other “pipes” that bring warmer water into the ice sheet in summer.

“The key difference between our model and previous models is that we include heat exchange between water flowing through the ice sheet and the ice,” said Rajaram.

Several factors contributed to the warming and resulting acceleration of ice flow, including the fact that flowing water into the ice sheets can stay in liquid form even through the winter, slowing seasonal cooling. In addition, warmer ice sheets are more susceptible to increases of water flow, including the basal lubrication of ice that allows ice to flow more readily on bedrock.

A third factor is melt water cascading downward into the ice, which warms the surrounding ice. In this process the water can refreeze, creating additional cracks in the more vulnerable warm ice, according to the study.

Taken together, the interactions between water, temperature, and ice velocity spell even more rapid changes to ice sheets in a changing climate than currently anticipated, the authors concluded. After comparing observed temperature profiles from Greenland with the new model described in the paper, the authors concluded the observations were unexplainable unless they accounted for warming.

“The fact that the ice temperatures warm rather quickly is really the key piece that’s been overlooked in models currently being used to determine how Greenland responds to climate warming,” Steffen said. “However, this process is not the ‘death knell’ for the ice sheet. Even under such conditions, it would still take thousands of years for the Greenland ice sheet to disappear, Steffen said.

This study was funded by NASA’s Cryosphere Science Program.

Source Science Daily

Satellite imagery from the European Space Agency shows that a massive iceberg that calved from Greenland’s Petermann Glacier on August 4 has cruised into the Nares Strait, putting 28 kilometers between it and its source.

The 245-square-kilometer iceberg – that’s about four times the size of Manhattan – faces a fractured future. The satellite imagery shows it has hit a small island, which is slowing its journey but also threatening to break it up.

The berg is being tracked by the European Space Agency’s Envisat satellite, using both radar and photographs.

Related stories

Massive Ice Island Breaks off Greenland

Greenland Ice Sheet faces a tipping point in 10 years

The entire ice mass of Greenland will disappear from the world map if temperatures rise by as little as 2C, with severe consequences for the rest of the world, a panel of scientists told Congress today.

Greenland shed its largest chunk of ice in nearly half a century last week, and faces an even grimmer future, according to Richard Alley, a geosciences professor at Pennsylvania State University

“Sometime in the next decade we may pass that tipping point which would put us warmer than temperatures that Greenland can survive,” Alley told a briefing in Congress, adding that a rise in the range of 2C to 7C would mean the obliteration of Greenland’s ice sheet.

The fall-out would be felt thousands of miles away from the Arctic, unleashing a global sea level rise of 23ft (7 metres), Alley warned. Low-lying cities such as New Orleans would vanish.

“What is going on in the Arctic now is the biggest and fastest thing that nature has ever done,” he said.

Speaking by phone, Alley was addressing a briefing held by the House of Representatives committee on energy independence and global warming.

Greenland is losing ice mass at an increasing rate, dumping more icebergs into the ocean because of warming temperatures, he said.

The stark warning was underlined by the momentous break-up of one of Greenland’s largest glaciers last week, which set a 100 sq mile chunk of ice drifting into the North Strait between Greenland and Canada.

The briefing also noted that the last six months had set new temperature records.

Robert Bindschadler, a research scientist at the University of Maryland, told the briefing: “While we don’t believe it is possible to lose an ice sheet within a decade, we do believe it is possible to reach a tipping point in a few decades in which we would lose the ice sheet in a century.”

The ice loss from the Petermann Glacier was the largest such event in nearly 50 years, although there have been regular and smaller “calvings”.

Petermann spawned two smaller breakaways: one of 34 sq miles in 2001 and another of 10 sq miles in 2008.

Andreas Muenchow, professor of ocean science at the University of Delaware, who has been studying the Petermann glacier for several years, said he had been expecting such a break, although he did not anticipate its size.

He also argued that much remains unknown about the interaction between Arctic sea ice, sea level, and temperature rise.

Muenchow told the briefing that over the last seven years he had only received funding to measure ocean temperatures near the Petermann Glacier for a total of three days.

He was also reduced, because of a lack of funding, to paying his own airfare and that of his students to they could join up with a Canadian icebreaker on a joint research project in the Arctic. 

Greenland's Petermann Glacier in 2009. Researchers say a quarter of the ice shelf has broken away.

August 7^th — A piece of ice four times the size of Manhattan island has broken away from an ice shelf in Greenland, according to scientists in the U.S.

The 260 square-kilometer (100 square miles) ice island separated from the Petermann Glacier in northern Greenland early on Thursday, researchers based at the University of Delaware said.

The ice island, which is about half the height of the Empire State Building, is the biggest piece of ice to break away from the Arctic icecap since 1962 and amounts to a quarter of the Petermann 70-kilometer floating ice shelf, according to research leader Andreas Muenchow.

“The freshwater stored in this ice island could keep the Delaware or Hudson rivers flowing for more than two years. It could also keep all U.S. public tap water flowing for 120 days,” Muenchow said.

Muenchow’s team is studying ice in the Nares Strait separating Greenland from Canada, about 1,000 kilometers south of the North Pole.

Satellite data from NASA’s MODIS-Aqua satellite revealed the initial rupture which was confirmed within hours by Trudy Wohlleben of the Canadian Ice Service, according to the University of Delaware website.

Muenchow said the island could block the Nares Strait as it drifts south, or break into smaller islands and continue towards the open waters of the Atlantic.

“In Nares Strait, the ice island will encounter real islands that are all much smaller in size,” he said.

“The newly born ice island may become land-fast, block the channel, or it may break into smaller pieces as it is propelled south by the prevailing ocean currents. From there, it will likely follow along the coasts of Baffin Island and Labrador, to reach the Atlantic within the next two years.”

Environmentalists say ice melt is being caused by global warming with Arctic temperatures in the 1990s reaching their warmest level of any decade in at least 2,000 years, according to a study published in 2009.

Current trends could see the Arctic Ocean become ice free in summer months within decades, researchers predict.

Source CNN

Events such as this one are not unusual, but rarely do scientists see them unfold in near real-time. Researchers working with the space agency spotted the rapid ice loss using high-resolution satellite imagery. Two such images tell the story. In the first image (above), a rift, which looks like a narrow horizontal line indicated by the red arrow, can be seen developing in the glacier. In the next image, taken a day later, the ice below the rift has collapsed into the sea and the location of the calving front has retreated.

Why does this glacier matter to me, you ask?

The short answer: sea level, although this particular event won’t raise the level of the Potomac or any other U.S. river anytime soon. Unlike the loss of sea ice, glacial melting causes sea level to increase, and the fate of glaciers like this one will play a key role in determining by how much sea level increases.

The Jakobshavn Isbrae is what is known as an outlet glacier, which the National Snow and Ice Data Center defines as “a valley glacier which drains an inland ice sheet or ice cap and flows through a gap in peripheral mountains.” In other words, it serves as a drainage pipe from the land ice into the ocean. According to NASA, the Jakobshavn Isbrae, which is located in western Greenland at about 69 degrees north latitude, is the largest outlet glacier in Greenland, draining 6.5 percent of Greenland’s ice sheet area.

Scientists at NASA, NOAA and other agencies are keeping close tabs on Greenland’s ice due to its significant ramifications for global sea level rise. If the entire Greenland ice sheet were to melt (a process that would likely take several centuries to play out, even with more global warming than we’ve already seen), sea level would rise by as much as an estimated 23 feet globally. NASA reports that “as much as 10 percent of all ice lost from Greenland is coming through Jakobshavn, which is also believed to be the single largest contributor to sea level rise in the northern hemisphere.”

Interestingly, this particular glacier has been retreating especially rapidly in recent years. As the below image shows, the ice front receded more 27 miles in 160 years, but in recent years the ice loss rate has increased, with six miles of retreat observed in just the past decade.

Recent studies have found that warming ocean temperatures may be responsible for much of the increased melting of Greenland’s outlet glaciers, and this may be accelerating the melting of the larger Greenland ice sheet. For example, one study published in Nature Geoscience in February concluded that glaciers in west Greenland are melting 100 times faster at their undersea end points than on the surface.

This event would support the ocean-driven melt theory, according to a NASA ice specialist.

“While there have been ice breakouts of this magnitude from Jakonbshavn and other glaciers in the past, this event is unusual because it occurs on the heels of a warm winter that saw no sea ice form in the surrounding bay,” said Thomas Wagner, cryospheric program scientist at NASA Headquarters, in a press release. “While the exact relationship between these events is being determined, it lends credence to the theory that warming of the oceans is responsible for the ice loss observed throughout Greenland and Antarctica.”

According to the study, some coastal areas are going up by nearly one inch per year and if current trends continue, that number could accelerate to as much as two inches per year by 2025, explains Tim Dixon, professor of geophysics at the University of Miami Rosenstiel School of Marine and Atmospheric Science (RSMAS) and principal investigator of the study.

“It’s been known for several years that climate change is contributing to the melting of Greenland’s ice sheet,” Dixon says. “What’s surprising, and a bit worrisome, is that the ice is melting so fast that we can actually see the land uplift in response,” he says. “Even more surprising, the rise seems to be accelerating, implying that melting is accelerating.”

Dixon and his collaborators share their findings in a new study titled “Accelerating uplift in the North Atlantic region as an indicator of ice loss,” The paper is now available as an advanced online publication, by Nature Geoscience. The idea behind the study is that if Greenland is losing its ice cover, the resulting loss of weight causes the rocky surface beneath to rise. The same process is affecting the islands of Iceland and Svalbard, which also have ice caps, explains Shimon Wdowinski, research associate professor in the University of Miami RSMAS, and co-author of the study.

“During ice ages and in times of ice accumulation, the ice suppresses the land,” Wdowinski says. “When the ice melts, the land rebounds upwards,” he says. “Our study is consistent with a number of global warming indicators, confirming that ice melt and sea level rise are real and becoming significant.”

Using specialized global positioning system (GPS) receivers stationed on the rocky shores of Greenland, the scientists looked at data from 1995 onward. The raw GPS data were analyzed for high accuracy position information, as well as the vertical velocity and acceleration of each GPS site.

The measurements are restricted to places where rock is exposed, limiting the study to coastal areas. However, previous data indicate that ice in Greenland’s interior is in approximate balance: yearly losses from ice melting and flowing toward the coast are balanced by new snow accumulation, which gradually turns to ice. Most ice loss occurs at the warmer coast, by melting and iceberg calving and where the GPS data are most sensitive to changes. In western Greenland, the uplift seems to have started in the late 1990′s.

Melting of Greenland’s ice contributes to global sea level rise. If the acceleration of uplift and the implied acceleration of melting continue, Greenland could soon become the largest contributor to global sea level rise, explains Yan Jiang, Ph.D. candidate at the University of Miami RSMAS and co-author of the study.

“Greenland’s ice melt is very important because it has a big impact on global sea level rise,” Jiang says. “We hope that our work reaches the general public and that this information is considered by policy makers.”

This work was supported by the National Science Foundation and NASA. The team plans to continue its studies, looking at additional GPS stations in sensitive coastal areas, where ice loss is believed to be highest.

Source Science Daily

I’m talking at the University of Queensland next week so I thought I might use Skeptical Science to test-drive a new visual metaphor. Sometimes in the climate debate, we get a bit lost in the data and statistical analysis, forgetting the sheer scale of the impact we’re having on our climate. A vivid example is the amount of ice that Greenland is currently losing. When scientists talk about ice loss from the Greenland ice sheet, they refer to gigatonnes of ice. One gigatonne is one billion tonnes. To get a picture of how large this is, imagine a block of ice one kilometre high by one kilometer wide by one kilometre deep (okay, the edges are actually 1055 metres long as ice is slightly less dense than water but you get the idea). Borrowing from alien invasion movies, the scale is well illustrated by comparing a gigatonne block of ice to a famous, historical landmark like the Empire State Building:

How much ice is Greenland losing? This is monitored by satellites which have measured changes in gravity around the ice sheet over the last decade (Velicogna 2009). In 2002 to 2003, the Greenland ice sheet was losing mass at a rate of 137 gigatonnes per year.

However, the rate of ice loss has more than doubled in less than a decade. The rate of ice loss over the 2008 to 2009 period was 286 gigatonnes per year.

This is a vivid reminder that global warming isn’t a statistical abstraction cooked up in a climate lab. Greenland is just one example of the physical realities of climate change. On the other side of the planet, Antarctica is also losing ice at an accelerating rate. All over the globe, glaciers are retreating at an accelerating rate.

It’s also a reminder of the massive amount of inertia at play in our climate. It takes time for the massive Greenland ice sheet to respond to warming. But this inertia is not our friend. Now that Greenland is losing ice at an accelerating rate, it’s not like we can throw a rope around the ice sheet and hold it back. The steadily accelerating ice loss from Greenland is an ominous reminder that our actions now will have effects long into the future.

And for those who wish to watch it happen in real time, here it is!

Why is Greenland losing ice? It appears linked in several ways to climate warming, which is strongest in the Arctic. First, surface melt of ice on Greenland has been increasing. Second, much of the meltwater drains to the base of glaciers and then lubricates the glaciers’ flow toward the sea. And finally, where the glaciers plunge into the ocean, warmer water appears to be eroding the glacial tongues that help hold flow back.

How do we know Greenland has been losing ice on balance? Data from two satellite missions have independently led to the same conclusion. ICESat has repeatedly measured the elevation profile of the Greenland Ice Sheet in great detail; changes over time, combined with estimates of ice compression and density, have allowed scientists to track changes in mass.Separately, the GRACE mission has provided a direct measure of mass change through time, through its unique “scale in the sky” capabilities, and is the basis for the 2004-2007 average annual loss estimate shown here.1 For years from before ICESat and GRACE, scientists used satellite radar altimetry and aircraft laser measurements to estimate Greenland’s ice mass, arriving at the figures shown here2—essentially no change in the 1990s.

This graphic is based on an estimated loss of 708 billion metric tons of ice from Greenland from 2004-2007.3

ICESat: Launched in January 2003, NASA’s Ice, Cloud and land Elevation Satellite (ICESat) carries laser altimeters capable of measuring the height of objects on and above Earth within an accuracy of roughly one inch, from an orbit over 400 miles high. The final laser out of three stopped working in October 2009; together, the lasers have completed just shy of two billion measurements, tracking small and large changes over time in the elevation of Arctic sea ice and of Greenland and Antarctic ice sheets, as well as cloud and aerosol heights, land topography, vegetation, and more.

GRACE: Launched in March 2002, NASA’s Gravity Recovery and Climate Experiment mission (GRACE) deploys two satellites that orbit the Earth in tandem. The pair measure the distance separating each other to an accuracy of 1% of the width of a human hair — and they orbit as far apart as Washington, DC and Philadelphia. Because each satellite accelerates or decelerates depending on the mass of the area beneath it (for example, a massive mountain range vs. flat lowlands), and because one satellite trails the other at some distance, the record of the shifting distance between them can be read like a giant planetary scale. And since they orbit over the same areas every ten days, the GRACE satellites provide a detailed record of mass changes in time, even tracking the seasonal accumulation and melting of Arctic snow.

Source Climate Central

Source MSNBC

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In recent years scientists have learned that liquid water lurks under much of Antarctica’s massive ice sheet, and so, they say, the potential microbial habitat in this watery world is huge. If the methane produced by the bacteria gets trapped beneath the ice and builds up over long periods of time — a possibility that is far from certain — it could mean that as ice sheets melt under warmer temperatures, they would release large amounts of heat-trapping methane gas.

Jemma Wadham, a geochemist at the University of Bristol in England, described the little-known role of methane-making microbes, called methanogens, below ice sheets on March 15 at an American Geophysical Union conference on Antarctic lakes.

Her team took samples from one site in Antarctica, the Lower Wright glacier, and one in Greenland, the Russell glacier. Trapped within the ice were high concentrations of methane, Wadham said, as well as methanogens themselves — up to 10 million cells per gram in the Antarctic sample and 100,000 cells per gram in Greenland. That’s comparable to the concentration of methanogens found in deep-ocean sediments, she said. The species of microbes were also similar to those found in other polar environments, such as Arctic peat or tundra.

The team then put scrapings from both sites into bottles and incubated them with water to see which microbes might grow. For the Antarctic samples, Wadham said, “nothing happens for 250 days and then bam! You get tons of methane.” The Greenland samples haven’t been growing for as long and so far don’t show much signs of giving off methane — but perhaps they just need more time, she reported at the meeting.

Other researchers have also recently found methanogens in icy settings. Mark Skidmore, a microbiologist at Montana State University in Bozeman, reported at the conference that his team has found methanogens in the Robertson glacier in the Canadian Rockies. “It underscores the importance of subglacial methanogenesis,” Skidmore said.

The studies flesh out a picture of Antarctica as a much more dynamic and watery environment than the frozen, static one once envisaged. At least 386 lakes have been identified buried beneath the ice sheet, scientists from the University of Edinburgh reported at the meeting. Plans for major drilling projects are underway for several of them.

Images: 1) NASA. 2) Zina Deretsky/NSF. 

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