Sea Ice in the Arctic Not Recovering: Another Critical Minimum Forecast

A critical minimum for Arctic sea ice can again be expected for late summer 2010, according to researchers.

Scientists from the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association (AWI) in Bremerhaven and from KlimaCampus of the University of Hamburg have now published data in this context in the annual issue of Sea Ice Outlook. The online publication compares the forecasts on ice cover for September 2010 prepared by around a dozen international research institutes in a scientific "competition." The ice reaches its minimum area at this time every year.

The forecast developed by the team from KlimaCampus of the University of Hamburg, i.e. 4.7 million square kilometres (km²), is more negative than that submitted by the AWI researchers, who arrived at a figure of 5.2 million km². Nevertheless, neither of the two research groups anticipates that the record minimum of 4.3 million km² in 2007 will be reached.

Although Arctic ice currently has an area of ten million km², which is half a million km² smaller than in 2007, one cannot directly conclude a new record minimum in late summer. The present ice cover is comparable to that in June 2006, a year when more ice area remained in September than in 2007. The decisive factors for the situation in late summer, such as the ice thickness in the central Arctic and further development of the weather in summer, are not yet known, however.

There is no reason for an all-clear: scientists basically assume a long-term decrease in sea ice cover for the northern polar region in the summers of the coming decades. Even though the trend in terms of area points slightly upward (2007: 4.3 million km², 2008: 4.68 million km², 2009: 5.36 million km²), the Arctic ice area from 1980 to 1990 was constantly greater than seven million km².

The two teams of scientists prepared their forecasts using different methods. Prof. Rüdiger Gerdes and his team from the Alfred Wegener Institute in conjunction with the scientific companies OASys and FastOpt jointly developed a model based on observation data from oceanic drift buoys and satellite data on ice measurement and ice movement. In the course of the summer the submitted forecast will be repeated on a monthly basis taking into account up-to-date weather data. "Currently we calculate that with 80% probability the ice cover in September will be between 4.7 and 5.7 million km2. However, the forecast will be more and more precise," says Prof. Rüdiger Gerdes.

The forecast developed by the KlimaCampus team headed by Prof. Lars Kaleschke, on the other hand, compares the ice area on every day of the year 2010 to that on the respective day from 2009 to 2003 on the basis of satellite pictures. The number and size of the ice-free areas, so-called polynyas, are indicators for later ice development. These dark ocean areas store solar energy already in early summer and thus additionally reinforce further melting during the polar summer, in which the sun no longer disappears, up to September. Alfred Wegener Institute (2010, June 24). Sea ice in the Arctic not recovering: Another critical minimum forecast. ScienceDaily. Retrieved June 28, 2010, from http://www.sciencedaily.com/releases/2010/06/100624112306.htm

Arctic Ice at Low Point Compared to Recent Geologic History

Less ice covers the Arctic today than at any time in recent geologic history. That's the conclusion of an international group of researchers, who have compiled the first comprehensive history of Arctic ice.
For decades, scientists have strived to collect sediment cores from the difficult-to-access Arctic Ocean floor, to discover what the Arctic was like in the past. Their most recent goal: to bring a long-term perspective to the ice loss we see today.
Now, in an upcoming issue of Quarternary Science Reviews, a team led by Ohio State University has re-examined the data from past and ongoing studies -- nearly 300 in all -- and combined them to form a big-picture view of the pole's climate history stretching back millions of years.
"The ice loss that we see today -- the ice loss that started in the early 20th Century and sped up during the last 30 years -- appears to be unmatched over at least the last few thousand years," said Leonid Polyak, a research scientist at Byrd Polar Research Center at Ohio State University. Polyak is lead author of the paper and a preceding report that he and his coauthors prepared for the U.S. Climate Change Science Program.
Satellites can provide detailed measures of how much ice is covering the pole right now, but sediment cores are like fossils of the ocean's history, he explained.
"Sediment cores are essentially a record of sediments that settled at the sea floor, layer by layer, and they record the conditions of the ocean system during the time they settled. When we look carefully at various chemical and biological components of the sediment, and how the sediment is distributed -- then, with certain skills and luck, we can reconstruct the conditions at the time the sediment was deposited."
For example, scientists can search for a biochemical marker that is tied to certain species of algae that live only in ice. If that marker is present in the sediment, then that location was likely covered in ice at the time. Scientists call such markers "proxies" for the thing they actually want to measure -- in this case, the geographic extent of the ice in the past.
While knowing the loss of surface area of the ice is important, Polyak says that this work can't yet reveal an even more important fact: how the total volume of ice -- thickness as well as surface area -- has changed over time.
"Underneath the surface, the ice can be thick or thin. The newest satellite techniques and field observations allow us to see that the volume of ice is shrinking much faster than its area today. The picture is very troubling. We are losing ice very fast," he said.
"Maybe sometime down the road we'll develop proxies for the ice thickness. Right now, just looking at ice extent is very difficult."
To review and combine the data from hundreds of studies, he and his cohorts had to combine information on many different proxies as well as modern observations. They searched for patterns in the proxy data that fit together like pieces of a puzzle.
Their conclusion: the current extent of Arctic ice is at its lowest point for at least the last few thousand years.
As scientists pull more sediment cores from the Arctic, Polyak and his collaborators want to understand more details of the past ice extent and to push this knowledge further back in time.
During the summer of 2011, they hope to draw cores from beneath the Chukchi Sea, just north of the Bering Strait between Alaska and Siberia. The currents emanating from the northern Pacific Ocean bring heat that may play an important role in melting the ice across the Arctic, so Polyak expects that the history of this location will prove very important. He hopes to drill cores that date back thousands of years at the Chukchi Sea margin, providing a detailed history of interaction between oceanic currents and ice.
"Later on in this cruise, when we venture into the more central Arctic Ocean, we will aim at harvesting cores that go back even farther," he said. "If we could go as far back as a million years, that would be perfect."
Polyak's coauthors on the report hailed from Penn State University, University of Colorado, University of Massachusetts, the U.S. Geological Survey, Old Dominion University, the Geological Survey of Canada, University of Copenhagen, the Cooperative Institute for Research in Environmental Sciences, Stockholm University, McGill University, James Madison University, and the British Antarctic Survey.
This research was funded by the US Geological Survey and the National Science Foundation.

Winds from Siberia Reduce Arctic Sea Ice Cover, Norwegian Researchers Find

The ice cover in the Arctic has decreased dramatically in recent years. Norwegian researchers have discovered that changes in air circulation patterns create winds that push away the ice.

n recent years, satellite images have shown large variations in the ice cover around the North Pole. The images have also shown that the ice cover in the Arctic has diminished considerably over the past 30 years, with the most drastic reductions occurring in recent years.

Many experts believe that it is now only a matter of decades before climate change results in a totally ice-free Arctic during parts of the year. For instance, the UN Intergovernmental Panel on Climate Change (IPCC) projects that this may occur by the end of this century.

How much of the change in ice cover is caused by dramatic changes in the climate, and how much is the result of other factors? And what is causing the ice cover in the Arctic to disappear even faster than the climate models project?

The Arctic climate paradox

A few years ago, US researchers discovered what they termed the "Arctic climate paradox." Since 1980, the researchers had been observing a decrease in ice cover. They explained this through a slow process of climate change combined with fluctuations in patterns of atmospheric pressure and air currents over the Arctic. It was believed that the positive phase of the Arctic Oscillation (AO) was a major cause of the receding ice cover.

The AO is normally influenced by three pressure systems located over the Azores, Iceland and the Northern Pacific Ocean. Since 2000 the AO has been in a negative phase. As a result, researchers predicted that the pace of reduction in the ice cover would slow down.

Instead it accelerated.

Unknown factor

"The US researchers argued that the ice was responding to something else, another factor that nobody had considered," explains Asgeir Sorteberg, Associate Professor at the Geophysical Institute at the University of Bergen. He has been investigating this phenomenon along with his colleagues in the project entitled the Norwegian Component of the Ecosystem Studies of Sub-Arctic Seas (NESSAS).

When the Norwegian researchers began their work, they noticed in particular a dramatic change in the weather pattern in the Arctic beginning about the year 2000. The change corresponded to the point in time when the reduction of ice cover in the Arctic began to accelerate.

The researchers began to analyze the circulation patterns over the Arctic.

"We found that these patterns can explain in large part why the ice cover decreased so much more rapidly after 2000. Wind patterns depend on the position of major high-pressure and low-pressure systems. We discovered that months with very little ice cover and high temperatures corresponded with crucial variations in the wind patterns," explains Mr Sorteberg.

"Up until 2000, the Arctic Oscillation (AO) had the greatest impact on the winter ice cover in the Arctic. But the change around 2000 meant that more of the weather and wind over the Arctic after that year was determined by high-pressure and low-pressure systems in northern Russia. In other words, the AO, which was usually so crucial, played a much less important role."

Ice is pushed away

"We have now managed to document what has occurred in connection with this change," says Mr Sorteberg.

The changed wind direction pushes large ice masses away from the Arctic and down along the eastern coast of Greenland. At the same time, less ice forms when the winds over the Arctic are determined by the pressure systems in northern Russia rather than those over the North Atlantic and the Pacific Ocean, as is normally the case.

The conclusion from this research is that we should be cautious about using the extent of the ice cover as an indicator of the ice's climatic "state of health."

The extent of the ice cover is highly dependent on the wind direction, and short-term changes in the ice cover give very little indication of whether climate change is occurring in the Arctic.

"The dramatic changes in the extent of Arctic sea ice in recent years have mainly been caused by atmospheric circulation patterns that have tended to reduce ice cover, combined with a slow process of climate change. Variations in the circulation patterns are part of the natural fluctuations in the weather. In certain periods these fluctuations will reinforce human-made changes, while at other times they will mask them," says Mr Sorteberg.

Climate change leads to thinner ice

Mr Sorteberg believes we should be cautious about interpreting the dramatic decrease in Arctic ice cover in the past decade as an indication that the Arctic will be ice free in 10 to 20 years.

However, he emphasizes that he and his colleagues do not reject the assertion that climate change is affecting Arctic ice cover or that the IPCC is wrong when it states that the Arctic may be nearly ice free in summer towards the end of this century.

"There is no doubt that the Arctic sea ice has become thinner in recent years. The thickness of the sea ice is a much better indicator than the extent of the ice cover if we want to study how climate change may affect the ice in the Arctic," says Mr Sorteberg.

Research Council of Norway (2010, April 28). Winds from Siberia reduce Arctic sea ice cover, Norwegian researchers find. ScienceDaily. Retrieved April 29, 2010, from http://www.sciencedaily.com­ /releases/2010/04/100427111449.htm

New Study Reveals, Melting Sea Ice Major Cause of Warming in Arctic

Melting sea ice has been shown to be a major cause of warming in the Arctic according to a University of Melbourne, Australia study.

Findings published in Nature reveal the rapid melting of sea ice has dramatically increased the levels of warming in the region in the last two decades.

Lead author Dr James Screen of the School of Earth Sciences at the University of Melbourne says the increased Arctic warming was due to a positive feedback between sea ice melting and atmospheric warming.

"The sea ice acts like a shiny lid on the Arctic Ocean. When it is heated, it reflects most of the incoming sunlight back into space. When the sea ice melts, more heat is absorbed by the water. The warmer water then heats the atmosphere above it. "

"What we found is this feedback system has warmed the atmosphere at a faster rate than it would otherwise," he says.

Using the latest observational data from the European Centre for Medium-Range Weather Forecasting, Dr Screen was able to uncover a distinctive pattern of warming, highly consistent with the loss of sea ice.

"In the study, we investigated at what level in the atmosphere the warming was occurring. What stood out was how highly concentrated the warming was in the lower atmosphere than anywhere else. I was then able to make the link between the warming pattern and the melting of the sea ice."

The findings question previous thought that warmer air transported from lower latitudes toward the pole, or changes in cloud cover, are the primary causes of enhanced Arctic warming.

Dr Screen says prior to this latest data set being available there was a lot of contrasting information and inconclusive data.

"This current data has provided a fuller picture of what is happening in the region," he says.

Over the past 20 years the Arctic has experienced the fastest warming of any region on the planet. Researchers around the globe have been trying to find out why.

Researchers say warming has been partly caused by increasing human greenhouse gas emissions. At the same time, the Arctic sea ice has been declining dramatically. In summer 2007 the Arctic had the lowest sea ice cover on record. Since then levels have recovered a little but the long-term trend is still one of decreasing ice.

Professor Ian Simmonds, of the University's School of Earth Sciences and coauthor on the paper says the findings are significant.

"It was previously thought that loss of sea ice could cause further warming. Now we have confirmation this is already happening."

James A. Screen, Ian Simmonds. The central role of diminishing sea ice in recent Arctic temperature amplification. Nature, 2010; 464 (7293): 1334 DOI: 10.1038/nature09051

Massive Arctic Ice Cap Is Shrinking, Study Shows; Rate Accelerating Since 1985

Close to 50 years of data show the Devon Island ice cap, one of the largest ice masses in the Canadian High Arctic, is thinning and shrinking.

A paper published in the March edition of Arctic, the journal of the University of Calgary's Arctic Institute of North America, reports that between 1961 and 1985, the ice cap grew in some years and shrank in others, resulting in an overall loss of mass. But that changed 1985 when scientists began to see a steady decline in ice volume and area each year.
"We've been seeing more mass loss since 1985," says Sarah Boon, lead author on the paper and a Geography Professor at the University of Lethbridge. The reason for the change? Warmer summers.
The High Arctic is essentially a desert with low rates of annual precipitation. There is little accumulation of snow in the winter and cool summers, with temperatures at or below freezing, serve to maintain levels. Any increase of snow and ice takes years.
This delicate equilibrium is easily upset. One warm summer can wipe out five years of growth. And though the accelerated melting trend began in 1985, the last decade has seen four years with unusually warm summers -- 2001, 2005, 2007 and 2008.
"What we see during these warm summers is the extent of the melt is greater," says Boon about the results of a five-year remote sensing study that ran between 2000 and 2004.
The white surfaces of snow and ice reflect heat -- a process known as the albedo effect. Retreating ice exposes dark soil and gravel, which absorb heat and increase the melt rate of ice along the periphery of the cap. But it's not only the edges of the cap that are losing ice. At lower altitudes the ice is thinning as well.
Changes to the Devon ice cap, which covers approximately 14,400 sq. km, could have multiple impacts on everything from ship traffic to sea level.
There has already been an increase in the number of icebergs calving off from outlet glaciers that flow into the ocean. Boon explains that melt water runs between the bottom of the glacier and the ground, creating a slippery cushion that allows the glacier to slide forward more rapidly than it would in colder conditions.
"There are a lot of things we need to consider. One is the iceberg calving and its implications for shipping. These things don't just go away, they float out into the ocean," says Boon. A second area of concern is the contribution of increased glacier melt to rising sea level.
The work of Boon and her colleagues demonstrates the importance of long-term research. Work on Devon Island began in 1961 with researchers from the Arctic Institute of North America, including long-time Arctic scientist Roy 'Fritz' Koerner, who was part of the current study until his death in 2008. This ongoing research, which is continuing thanks to federal International Polar year funding, has created a comprehensive dataset that contributes to the understanding of the complex play between the ice cap, the atmosphere and the ocean.
"We all know long-term studies are important but they are really hard to pay for."

Arctic Institute of North America (2010, April 13). Massive Arctic ice cap is shrinking, study shows; Rate accelerating since 1985.

Ice Sheet Melt Identified as Trigger of 'Big Freeze'

The main cause of a rapid global cooling period, known as the Big Freeze or Younger Dryas -- which occurred nearly 13,000 years ago -- has been identified thanks to the help of an academic at the University of Sheffield.

A new paper, which is published in Nature on April 1, 2010, has identified a mega-flood path across North America which channelled melt-water from a giant ice sheet into the oceans and triggering the Younger Dryas cold snap.
The research team, which included Dr Mark Bateman from the University of Sheffield's Department of Geography, discovered that a mega-flood, caused by the melting of the Laurentide ice sheet, which covered much of North America, was routed up into Canada and into the Arctic Ocean.
This resulted in huge amounts of fresh water mixing with the salt water of the Arctic Ocean. As a result, more sea-ice was created which flowed into the North Atlantic, causing the northward continuation of the Gulf Stream to shut down.
Without the heat being brought across the Atlantic by the Gulf Stream, temperatures in Europe plunged from similar to what they are today, back to glacial temperatures with average winter temperatures of -25oC. This cooling event has become known as the Younger Dryas period with cold conditions lasting about 1400 years. The cold of the Younger Dryas affected many places across the continent, including Yorkshire in the Vale of York and North Lincolnshire which became arctic deserts with sand dunes and no vegetation.
Before now, scientists have speculated that the mega-flood was the main cause of the abrupt cooling period, but the path of the flood waters has long been debated and no convincing evidence had been found establishing a route from the ice-sheet to the North Atlantic.
The research team studied a large number of cliff sections along the Mackenzie Delta and examined the sediments within them. They found that many of the cliff sections showed evidence of sediment erosion. This evidence spanned over a large region at many altitudes, which could only be explained by a mega-flood from the over-spilling of Lake Agassiz, which was at times bigger than the UK, at the front of the Laurentide Ice-sheet rather than a normal flood of the river.
Dr Bateman, who has been researching past environmental changes both in the UK and elsewhere in the world for almost 20 years, runs the luminescence dating lab at Sheffield. The lab was able to take the MacKenzie Delta sediment samples from above and below the mega-flood deposits, and find out when the mega-flood occurred, enabling its occurrence to be attributed to the start of the Younger Dryas.
The study will help shed light on the implications of fresh water input into the North Atlantic today. There are current concerns that changes in the salinity of the ocean today, could cause another shut down of the Gulf Stream. Current climate changes, including global warming, may be altering the planetary system which regulates evaporation and precipitation, and moves fresh water around the globe.
The findings, which show the cause, location, timing and magnitude of the mega-flood, will enable scientists to better understand how sensitive both oceans and climates are to fresh-water inputs and the potential climate changes which may ensue if the North Atlantic continues to alter.
Dr Mark Bateman, from the University of Sheffield's Centre for International Drylands Research at the Department of Geography, said: "The findings of this paper through the combination of luminescence dating, landscape elevation models and sedimentary evidence allows an insight into what must have been one of the most catastrophic geological events in recent earth's history. They also show how events within the Earth-climate system in North America had huge impacts in Europe."
Julian B. Murton, Mark D. Bateman, Scott R. Dallimore, James T. Teller, Zhirong Yang. Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean. Nature, 2010; 464 (7289): 740 DOI: 10.1038/nature08954

Greenland Ice Sheet Losing Mass on Northwest Coast

Ice loss from the Greenland ice sheet, which has been increasing during the past decade over its southern region, is now moving up its northwest coast, according to a new international study.

Led by the Denmark Technical Institute's National Space Institute in Copenhagen and involving the University of Colorado at Boulder, the study indicated the ice-loss acceleration began moving up the northwest coast of Greenland starting in late 2005. The team drew their conclusions by comparing data from NASA's Gravity and Recovery Climate Experiment satellite system, or GRACE, with continuous GPS measurements made from long-term sites on bedrock on the edges of the ice sheet.
The data from the GPS and GRACE provided the researchers with monthly averages of crustal uplift caused by ice-mass loss. The team combined the uplift measured by GRACE over United Kingdom-sized chunks of Greenland while the GPS receivers monitor crustal uplift on scales of just tens of miles. "Our results show that the ice loss, which has been well documented over southern portions of Greenland, is now spreading up along the northwest coast," said Shfaqat Abbas Khan, lead author on a paper that will appear in Geophysical Research Letters.
The team found that uplift rates near the Thule Air Base on Greenland's northwest coast rose by roughly 1.5 inches, or about 4 centimeters, from October 2005 to August 2009. Although the low resolution of GRACE -- a swath of about 155 miles, or 250 kilometers across -- is not precise enough to pinpoint the source of the ice loss, the fact that the ice sheet is losing mass nearer to the ice sheet margins suggests the flows of Greenland outlet glaciers there are increasing in velocity, said the study authors.
"When we look at the monthly values from GRACE, the ice mass loss has been very dramatic along the northwest coast of Greenland," said CU-Boulder physics Professor and study co-author John Wahr, also a fellow at CU-Boulder's Cooperative Institute for Research in Environmental Sciences.
"This is a phenomenon that was undocumented before this study," said Wahr. "Our speculation is that some of the big glaciers in this region are sliding downhill faster and dumping more ice in the ocean."
Other co-authors on the new GRL study included Michael Bevis and Eric Kendrick from Ohio State University and Isabella Velicogna of the University of California-Irvine, who also is a scientist at NASA's Jet Propulsion Laboratory. GRL is published by the American Geophysical Union.
A 2009 study published in GRL by Velicogna, who is a former CU-Boulder research scientist, showed that between April 2002 and February 2009, the Greenland ice sheet shed roughly 385 cubic miles of ice. The mass loss is equivalent to about 0.5 millimeters of global sea-level rise per year.
"These changes on the Greenland ice sheet are happening fast, and we are definitely losing more ice mass than we had anticipated, " said Velicogna. "We also are seeing this ice mass loss trend in Antarctica, a sign that warming temperatures really are having an effect on ice in Earth's cold regions."
Researchers have been gathering data from GRACE since NASA launched the system in 2002. Two GRACE satellites whip around Earth 16 times a day separated by 137 miles and measure changes in Earth's gravity field caused by regional shifts in the planet's mass, including ice sheets, oceans and water stored in the soil and in underground aquifers.
"GRACE is unique in that it allows us to see changes in the ice mass in almost real time," said Velicogna. "Combining GRACE data with the separate signals from GPS stations gives us a very powerful tool that improves our resolution and allows us to better understand the changes that are occurring."
In addition to monitoring the Thule GPS receiver in northwest Greenland as part of the new GRL study, the team also is taking data from GPS receivers in southern Greenland near the towns of Kellyville and Kulusuk. An additional 51 permanent GPS stations recently set up around the edges of the Greenland ice sheet should be useful to measure future crustal uplift and corresponding ice loss, said Wahr.
"If this activity in northwest Greenland continues and really accelerates some of the major glaciers in the area -- like the Humboldt Glacier and the Peterman Glacier -- Greenland's total ice loss could easily be increased by an additional 50 to 100 cubic kilometers (12 to 24 cubic miles) within a few years," said Khan.
The study was funded by NASA and the National Science Foundation.
Greenland is about one-fourth the size of the United States and the massive ice sheet covers about 80 percent of its surface. It holds about 20 percent of the world's ice, the equivalent of about 21 feet of global sea rise. Air temperatures over the Greenland ice sheet have increased by about 4 degrees Fahrenheit since 1991, which most scientists attribute to a build-up of greenhouse gases in the atmosphere.
A 2006 study by Wahr and Velicogna using the GRACE satellite indicated that Greenland lost roughly 164 cubic miles of ice from April 2004 to April 2006 -- more than the volume of water in Lake Erie.

Surprise Shrimp Under Antarctic Ice

At a depth of 600 feet beneath the West Antarctic ice sheet, a small shrimp-like creature managed to brighten up an otherwise gray polar day in late November 2009.

This critter is a three-inch long Lyssianasid amphipod found beneath the Ross Ice Shelf, about 12.5 miles away from open water.
NASA scientists were using a borehole camera to look back up towards the ice surface when they spotted this pinkish-orange creature swimming beneath the ice.

Ice Shelves Disappearing on Antarctic Peninsula

Ice shelves are retreating in the southern section of the Antarctic Peninsula due to climate change, according to new data. This could result in glacier retreat and sea-level rise if warming continues, threatening coastal communities and low-lying islands worldwide, experts say.Research by the U.S. Geological Survey is the first to document that every ice front in the southern part of the Antarctic Peninsula has been retreating overall from 1947 to 2009, with the most dramatic changes occurring since 1990. The USGS previously documented that the majority of ice fronts on the entire Peninsula have also retreated during the late 20th century and into the early 21st century.The ice shelves are attached to the continent and already floating, holding in place the Antarctic ice sheet that covers about 98 percent of the Antarctic continent. As the ice shelves break off, it is easier for outlet glaciers and ice streams from the ice sheet to flow into the sea. The transition of that ice from land to the ocean is what raises sea level."This research is part of a larger ongoing USGS project that is for the first time studying the entire Antarctic coastline in detail, and this is important because the Antarctic ice sheet contains 91 percent of Earth's glacier ice," said USGS scientist Jane Ferrigno. "The loss of ice shelves is evidence of the effects of global warming. We need to be alert and continually understand and observe how our climate system is changing."The Peninsula is one of Antarctica's most rapidly changing areas because it is farthest away from the South Pole, and its ice shelf loss may be a forecast of changes in other parts of Antarctica and the world if warming continues.Retreat along the southern part of the Peninsula is of particular interest because that area has the Peninsula's coolest temperatures, demonstrating that global warming is affecting the entire length of the Peninsula.The Antarctic Peninsula's southern section as described in this study contains five major ice shelves: Wilkins, George VI, Bach, Stange and the southern portion of Larsen Ice Shelf. The ice lost since 1998 from the Wilkins Ice Shelf alone totals more than 4,000 square kilometers, an area larger than the state of Rhode Island.The USGS is working collaboratively on this project with the British Antarctic Survey, with the assistance of the Scott Polar Research Institute and Germany's Bundesamt fûr Kartographie und Geodäsie. The research is also part of the USGS Glacier Studies Project, which is monitoring and describing glacier extent and change over the whole planet using satellite imagery.The report, "Coastal-Change and Glaciological Map of the Palmer Land Area, Antarctica: 1947 -- 2009" and its accompanying map is available online (http://pubs.usgs.gov/imap/i-2600-c/).The other completed reports in the Coastal Change and Glaciological Maps of Antarctica series can be viewed online (http://pubs.usgs.gov/imap/2600/).

Ice Is 'Rotten' in the Beaufort Sea

Recent observations show that Beaufort Sea ice was not as it appeared in the summer of 2009. Sea ice cover serves as an indication of climate and has implications for marine and terrestrial ecosystems.

In early September 2009, satellite measurements implied that most of the ice in the Beaufort Sea either was thick ice that had been there for multiple years or was thick, first-year ice.

However, in situ observations made in September 2009 by Barber et al. show that much of the ice was in fact "rotten" ice -- ice that is thinner, heavily decayed, and structurally weak due to a uniform temperature throughout.

The authors suggest that satellite measurements were confused because both types of ice exhibit similar temperature and salinity profiles near their surfaces and a similar amount of open water between flows. The authors note that while an increase in summer minimum ice extent in the past 2 years could give the impression that Arctic ice is recovering, these new results show that multiyear ice in fact is still declining.

The results have implications for climate science and marine vessel transport in the Arctic.

The research appears in the journal Geophysical Research Letters.

Authors include David G. Barber, Ryan Galley, Matthew G. Asplin, Kerri-Ann Warner and Mukesh Gupta, Centre for Earth Observation Science, Faculty of Environment, Earth and Resources, University of Manitoba; Roger De Abreu, Canadian Ice Service, Environment Canada; Monika Pućko, Centre for Earth Observation Science, Faculty of Environment, Earth and Resources, University of Manitoba, and Freshwater Institute, Fisheries and Oceans; Simon Prinsenberg, Bedford Institute of Oceanography, Fisheries and Oceans; Stéphane Julien, Laurentian Region, Canadian Coast Guard.

Tipping Point? West Antarctic Ice Sheet Could Become Unstable as World Warms

A new study examines how ice sheets, such as the West Antarctic Ice Sheet, could become unstable as the world warms.

The team from Oxford University and Cambridge University developed a model to explore how changes in the 'grounding line' -- where an ice sheet floats free from its base of rock or sediment -- could lead to the disintegration of ice sheets and result in a significant rise in global sea level.

'The volume of ice locked up in the West Antarctic Ice Sheet is equivalent to a sea level rise of around 3.3 metres,' said Dr Richard Katz of Oxford University's Department of Earth Sciences, an author of the report. 'Our model shows how instability in the grounding line, caused by gradual climatic changes, has the potential to reach a 'tipping point' where disintegration of the ice sheet could occur.'

At the moment the model -- that uniquely takes into account the three dimensional shape of ice sheets -- is still fairly simple, but the researchers hope to eventually include more detail on how ice sheets interact with their base slopes and show the behaviour of individual ice streams.

When the team applied their theoretical and mathematical model to the West Antarctic Ice Sheet they found that, contrary to earlier assessments, a scenario which would see instability grow as the grounding line recedes was likely. In the case of the Pine Island Glacier it may already be occurring.

'Global climate models often assume that, as the world warms, ice sheets will melt at a steady rate, leading to gradual rises in sea level -- but ice sheets are much more complex structures than this,' said Dr Katz. 'We need to do a lot more work to build better models of how ice sheets behave in the real world. Only then can we start to predict how this behaviour might change in the future as the climate changes.'

A report of the research, 'Stability of ice sheet grounding lines', is published in Proceedings of the Royal Society A. The research was conducted by Dr Richard Katz of Oxford University's Department of Earth Sciences and Professor M Grae Worster of Cambridge University's Institute of Theoretical Geophysics.

Tipping Point? West Antarctic Ice Sheet Could Become Unstable as World Warms

A new study examines how ice sheets, such as the West Antarctic Ice Sheet, could become unstable as the world warms.

The team from Oxford University and Cambridge University developed a model to explore how changes in the 'grounding line' -- where an ice sheet floats free from its base of rock or sediment -- could lead to the disintegration of ice sheets and result in a significant rise in global sea level.
'The volume of ice locked up in the West Antarctic Ice Sheet is equivalent to a sea level rise of around 3.3 metres,' said Dr Richard Katz of Oxford University's Department of Earth Sciences, an author of the report. 'Our model shows how instability in the grounding line, caused by gradual climatic changes, has the potential to reach a 'tipping point' where disintegration of the ice sheet could occur.'
At the moment the model -- that uniquely takes into account the three dimensional shape of ice sheets -- is still fairly simple, but the researchers hope to eventually include more detail on how ice sheets interact with their base slopes and show the behaviour of individual ice streams.
When the team applied their theoretical and mathematical model to the West Antarctic Ice Sheet they found that, contrary to earlier assessments, a scenario which would see instability grow as the grounding line recedes was likely. In the case of the Pine Island Glacier it may already be occurring.
'Global climate models often assume that, as the world warms, ice sheets will melt at a steady rate, leading to gradual rises in sea level -- but ice sheets are much more complex structures than this,' said Dr Katz. 'We need to do a lot more work to build better models of how ice sheets behave in the real world. Only then can we start to predict how this behaviour might change in the future as the climate changes.'
A report of the research, 'Stability of ice sheet grounding lines', is published in Proceedings of the Royal Society A. The research was conducted by Dr Richard Katz of Oxford University's Department of Earth Sciences and Professor M Grae Worster of Cambridge University's Institute of Theoretical Geophysics.

Arctic Could Face Warmer and Ice-Free Conditions

There is increased evidence that the Arctic could face seasonally ice-free conditions and much warmer temperatures in the future.

Scientists documented evidence that the Arctic Ocean and Nordic Seas were too warm to support summer sea ice during the mid-Pliocene warm period (3.3 to 3 million years ago). This period is characterized by warm temperatures similar to those projected for the end of this century, and is used as an analog to understand future conditions.
The U.S. Geological Survey found that summer sea-surface temperatures in the Arctic were between 10 to 18°C (50 to 64°F) during the mid-Pliocene, while current temperatures are around or below 0°C (32°F).
Examining past climate conditions allows for a true understanding of how Earth's climate system really functions. USGS research on the mid-Pliocene is the most comprehensive global reconstruction for any warm period. This will help refine climate models, which currently underestimate the rate of sea ice loss in the Arctic.
Loss of sea ice could have varied and extensive consequences, such as contributions to continued Arctic warming, accelerated coastal erosion due to increased wave activity, impacts to large predators (polar bears and seals) that depend on sea ice cover, intensified mid-latitude storm tracks and increased winter precipitation in western and southern Europe, and less rainfall in the American west.
"In looking back 3 million years, we see a very different pattern of heat distribution than today with much warmer waters in the high latitudes," said USGS scientist Marci Robinson. "The lack of summer sea ice during the mid-Pliocene suggests that the record-setting melting of Arctic sea ice over the past few years could be an early warning of more significant changes to come."
Global average surface temperatures during the mid-Pliocene were about 3°C (5.5°F) greater than today and within the range projected for the 21st century by the Intergovernmental Panel on Climate Change.

Polar Bears Changing Habitat in Response to Sea Ice Conditions

A long-term study showing the changes in habitat associations of polar bears in response to sea ice conditions in the southern Beaufort Sea has implications for polar bear management in Alaska.

Karyn Rode, a polar bear biologist with the U.S. Fish and Wildlife Service in Anchorage, Alaska and one of the study's authors, says data collected between 1979 and 2005 show that polar bears in the region are occurring more frequently on land and in open water and less frequently on ice during the fall. This means there are increased chances for human/bear interaction. The paper was published in the December issue of Arctic -- the journal of the Arctic Institute of North America.

Polar bears were observed over the 27-year period by U.S. government Minerals Management Services staff as part of the fall bowhead whale aerial survey conducted annually in the southern Beaufort Sea. Ice conditions were also recorded.

Data showed that as ice conditions changed, bears were being found on different habitats. Between 1979 and 1987, 12% of bear sightings were associated with no ice. Between 1997 and 2005 however, 90% of bear sightings were associated with no ice.

"When bears were seen, they were more often seen in open water and on land than on sea ice. At the same time, changes were observed in ice, suggesting that these observations are connected," says Rode.

In addition, the number of bears sighted steadily increased from 138 bears in the years 1979-1987, to 271 bears between 1988 and 1996, and finally to 468 bears between 1997 and 2005. Rode warns that this study was not designed to estimate the number of bears using the nearshore area. Data were drawn from studies created to track bowhead whale migration routes, not polar bear populations. Therefore, it should not be concluded that more bears are occurring in the nearshore waters off the Southern Beaufort Sea coast.

However, Rode states that "Our results do suggest that bears that use the nearshore area are more likely to occur on land in recent years because their preferred habitat, sea ice, is unavailable.

"This is one of the few data sets available over such a long time frame. It shows there has been a shift in habitat use," she says.

In the Beaufort Sea region, there was less ice in 2005 than when the study period began in 1979. In general, freeze up is later and spring melt comes earlier with measurements showing since 1979 the summer melt period has increased by 13 days per decade. This is one reason for the region's rapid retreat of multi-year ice, which provides a thicker, more stable platform for hunting and denning.

This work is helpful in highlighting the need to proactively develop programs to manage bear-human interactions in coastal areas. Bear-human interactions in Native villages and with industry in Alaska have been on the rise in recent years.

This media release is part of the Promotion of Arctic Science, an Arctic Institute of North America project made possible with the generous support of the Government of Canada Program for International Polar Year.

The mission of the Arctic Institute of North America at the University of Calgary is to advance the study of the North American and circumpolar Arctic and to acquire, preserve and disseminate information on physical, environmental and social conditions in the North. More information can be found at www.arctic.ucalgary.ca

From greenhouse to icehouse reconstructing the environment of the Voring Plat

The analysis of microfossils found in ocean sediment cores is illuminating the environmental conditions that prevailed at high latitudes during a critical period of Earth history.

Around 55 million years ago at the beginning of the Eocene epoch, the Earth's poles are believed to have been free of ice. But by the early Oligocene around 25 million years later, ice sheets covered Antarctica and continental ice had developed on Greenland.

"This change from greenhouse to icehouse conditions resulted from decreasing greenhouse gas concentrations and changes in Earth's orbit," said Dr Ian Harding of the University of Southampton's School of Ocean and Earth Science (SOES) at the National Oceanography Centre, Southampton (NOCS): "However, the opening or closing of various marine gateways and shifts in ocean currents may also have influenced regional climate in polar high-latitudes."

The separation of Eurasia and Greenland due to shifting tectonic plates led to the partial or complete submergence of former land barriers such as the Vøring Plateau of the Norwegian continental margin. For the first time, waters could exchange between the Norwegian–Greenland Sea, the Arctic Ocean and the North Atlantic.

Dr Harding and his former PhD student Dr James Eldrett have reconstructed the environmental conditions over the Vøring Plateau over this time period by carefully analysing the fossilised remains of organic debris and cysts of tiny aquatic organisms called dinoflagellates from sediment cores.

"Because different dinoflagellate species are adapted to different surface water conditions, their fossilised remains help us reconstruct past environments," said Dr Harding.

The evidence from the sediments cores suggests the development of shallow marine environments across parts of the Vøring Plateau during the early Eocene. However, the presence of fossilised species that lived in fresh or brackish water indicates that northerly parts of the plateau as well as the crest of the Vøring Escarpment were still above water.

In the late Eocene sediments (around 44 million years old) only marine plankton species were found, indicating that the entire Vøring Plateau had by then subsided and become submerged. This demonstrates that marine connections were established between the various Nordic sea basins much earlier than had previously been thought. These surface water connections may have promoted the increased surface water productivity evidenced by the abundance of planktonic fossils preserved in the sediment cores of this age.

"Increased productivity would have drawn carbon dioxide down from the atmosphere," said Dr Harding: "Because carbon dioxide is a greenhouse gas, this may have contributed to declining global temperatures and led to the early development of continental ice on Greenland in the latest Eocene."

Earth's Polar Ice Sheets Vulnerable to Even Moderate Global Warming; New Orleans, Much of Southern Florida, Expected to Be Permanently Submerged

A new analysis of the geological record of the Earth's sea level, carried out by scientists at Princeton and Harvard universities and published in the Dec. 16 issue ofNature, employs a novel statistical approach that reveals the planet's polar ice sheets are vulnerable to large-scale melting even under moderate global warming scenarios. Such melting would lead to a large and relatively rapid rise in global sea level.

According to the analysis, an additional 2 degrees of global warming could commit the planet to 6 to 9 meters (20 to 30 feet) of long-term sea level rise. This rise would inundate low-lying coastal areas where hundreds of millions of people now reside. It would permanently submerge New Orleans and other parts of southern Louisiana, much of southern Florida and other parts of the U.S. East Coast, much of Bangladesh, and most of the Netherlands, unless unprecedented and expensive coastal protection were undertaken. And while the researchers' findings indicate that such a rise would likely take centuries to complete, if emissions of greenhouse gases are not abated, the planet could be committed during this century to a level of warming sufficient to trigger this outcome.

The study was written by Robert Kopp, who conducted the work as a postdoctoral researcher in Princeton's Department of Geosciences and Woodrow Wilson School of Public and International Affairs; Frederik Simons, an assistant professor of geosciences at Princeton; Jerry Mitrovica, a professor of geophysics at Harvard; Adam Maloof, an assistant professor of geosciences at Princeton; and Michael Oppenheimer, a professor of geosciences and international affairs in Princeton's Woodrow Wilson School.

As part of the study, the researchers compiled an extensive database of geological sea level indicators for a period known as the last interglacial stage about 125,000 years ago. Polar temperatures during this stage were likely 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) warmer than today, as is expected to occur in the future if temperatures reach about 2 to 3 degrees Celsius (about 4 to 6 degrees Fahrenheit) above pre-industrial levels.

"The last interglacial stage provides a historical analog for futures with a fairly moderate amount of warming; the high sea levels during the stage suggest that significant chunks of major ice sheets could disappear over a period of centuries in such futures," Kopp said. "Yet if the global economy continues to depend heavily on fossil fuels, we're on track to have significantly more warming by the end of century than occurred during the last interglacial. I find this somewhat worrisome."

Oppenheimer added, "Despite the uncertainties inherent in such a study, these findings should send a strong message to the governments negotiating in Copenhagen that the time to avoid disastrous outcomes may run out sooner than expected."

Previous geological studies of sea level benchmarks such as coral reefs and beaches had shown that, at many localities, local sea levels during the last interglacial stage were higher than today. But local sea levels differ from those in this earlier stage; one major contributing factor is that the changing masses of the ice sheets alter the planet's gravitational field and deform the solid Earth. As a consequence, inferring global sea level from local geological sea level markers requires a geographically broad data set, a model of the physics of sea level, and a means to integrate the two. The study's authors provide all three, integrating the data and the physics with a statistical approach that allows them to assess the probability distribution of past global sea level and its rate of change.

The researchers determined through their analysis that there is a 95 percent probability that, during the last interglacial stage, global sea level peaked more than 6.6 meters (22 feet) above its present level. They further found that it is unlikely (with a 33 percent probability) that global sea level during this period exceeded 9.4 meters (31 feet).

Sea levels during the last interglacial stage are of interest to scientists and important to policymakers for several reasons. Most notably, the last interglacial stage is relatively recent by geological standards, making it feasible for climate scientists to develop a credible sea level record for the period, and is the most recent time period when average global temperatures and polar temperatures were somewhat higher than today. Because it was slightly warmer, the period can help scientists understand the stability of polar ice sheets and the future rate of sea level rise under low to moderate global warming scenarios.

The findings indicate that sea level during the last interglacial stage rose for centuries at least two to three times faster than the recent rate, and that both the Greenland and West Antarctic ice sheet likely shrank significantly and made important contributions to sea level rise. However, the relative timing of temperature change and sea level change during the last interglacial stage is fairly uncertain, so it is not possible to infer from the analysis how long an exposure to peak temperatures during this stage was needed to commit the planet to peak sea levels.

Icebergs head from Antarctica for New Zealand

A flotilla of hundreds of icebergs that split off Antarctic ice shelves is drifting toward New Zealand and could pose a risk to ships in the south Pacific Ocean, officials said Tuesday.The nearest one, measuring about 30 yards (meters) tall, was 160 miles (260 kilometers) southeast of New Zealand's Stewart Island, Australian glaciologist Neal Young said. He couldn't say how many icebergs in total were roaming the Pacific, but he counted 130 in one satellite image alone and 100 in another.Large numbers of icebergs last floated close to New Zealand in 2006, when some were visible from the coastline — the first such sighting since 1931.Maritime officials have issued navigation warnings for the area south of the country."It's an alert to shipping to be aware these potential hazards are around and to be on the lookout for them," Maritime New Zealand spokeswoman Sophie Hazelhurst said.No major shipping lanes or substantial fishing grounds are in the area, but most ships there have little hull protection if they collide with an iceberg — which typically has 90 percent of its mass under water. Very few adventure sailors would be in the waters in November, when it is still the southern hemisphere's spring.Icebergs are routinely sloughed off as part of the natural development of ice shelves, but Young said the rate appeared to be increasing as a result of regional warming in Antarctica."Whole ice shelves have broken up," he said, as temperatures have risen in Antarctica, where they are up as much as 5 degrees Fahrenheit (3 degrees Celsius) in the past 60 years.But he cautioned against linking the appearance of the bergs in New Zealand waters to global warming: The phenomenon depends as much on weather patterns and ocean currents as on the rate at which icebergs are calving off Antarctic ice shelves.In the current case, a cold snap around southern New Zealand and favorable ocean currents conspired to push the towering visitors, which have drifted around Antarctica for the past nine years, to the region intact."Icebergs this far north (near New Zealand) are not that unusual," said New Zealand glaciologist Dr. Wendy Lawson Lawson, noting that an iceberg's reach was determined by its size."If an iceberg starts off large, it will last longer in the sea. Its movement and where it ends up is determined by the weather, wind, ocean currents and the temperature," Lawson, head of the department of geography at Canterbury University, told The Associated Press.On Monday, Rodney Russ, expedition leader on the tourist ship Spirit of Enderby, spotted a 500-foot-long (150-meter-long) iceberg about 60 miles (100 kilometers) northeast of Macquarie Island and heading north — about 500 miles (800 kilometers) south of New Zealand. Australian scientists reported another mass of 20 icebergs drifting north past Macquarie Island two weeks ago.Young said satellite images showed the group of icebergs, spread over a sea area of 600 miles by 440 miles (1,000 kilometers by 700 kilometers), moving on ocean currents away from Antarctica.Icebergs are formed as the ice shelf develops. Snow falls on the ice sheet and forms more ice, which flows to the edges of the floating ice shelves. Eventually, pieces around the edge break off.

Peering Under The Ice Of Collapsing Polar Coast

Starting this month, a giant NASA DC-8 aircraft loaded with geophysical instruments and scientists will buzz at low level over the coasts of West Antarctica, where ice sheets are collapsing at a pace far beyond what scientists expected a few years ago. The flights, dubbed Operation Ice Bridge, are an effort by NASA in cooperation with university researchers to image what is happening on, and under, the ice, in order to estimate future sea-level rises that might result.

Since 2003, laser measurements of ice surfaces from NASA's ICESat satellite have shown that vast ice masses in Greenland and West Antarctica are thinning and flowing quickly seaward. Last month, a report in the journal Nature based on the satellite's measurements showed that some parts of the Antarctic area to be surveyed have been sinking 9 meters (27) feet a year; in 2002, one great glacial ice shelf jutting from land over the ocean on the Antarctic Peninsula simply disintegrated and floated away within days. NASA's satellite reaches the end of its life this year, and another will not go up until 2015; in the interim, Operation Ice Bridge flights will continue and expand upon the satellite mission.
In addition to lasers, the plane will carry penetrating radars to measure snow cover and the thickness of ice to bedrock, and a gravity-measuring system run by Columbia University's Lamont-Doherty Earth Observatory that will, for the first time, plot the geometry and depth of ocean waters under the ice shelves. The gravity study is seen as key because many scientists believe warm ocean currents may be the main force pulling the ice sheets seaward, melting the undersides of ice shelves and thus removing the buttresses that hold back the far greater masses of ice on land.
"What our colleagues see from modeling of these glaciers is that warm ocean water is providing the thermal energy to melt the ice," said Lamont geophysicist Michael Studinger, a co-leader of the gravity team who will be on some of the flights. "To really understand how the glaciers are going to behave, we need the firsthand measurements of water shape and depth." Earlier this year, an icebreaker cruise co-led by another Lamont scientist, Stan Jacobs, sent an automated submarine to look under the region's Pine Island Glacier, which has been moving forward rapidly in recent years. Its bed, where the ice contacts rock, is below sea level, and scientists are concerned about what would happen if a sudden large movement were to introduce seawater underneath. The plane flights, over some six weeks starting Oct. 15, are aimed at providing a wider-scale picture of Pine Island and other targets.
For each of some 17 flights, the 157-foot DC-8--too big for runways on Antarctic bases--will make an 11-hour round trip from Punta Arenas, Chile, with two-thirds of each trip spent getting to Antarctica. There, the plane will fly survey lines as low as 1,000 feet, some of them along sinuous glacial valleys that may test the nerves of both pilots and scientists. Some flights will investigate the region's open sea ice, which also seems to be in decline. The campaign will cost about $7 million.
"We learned how fast the ice sheets are changing from NASA satellites," said Lamont geophysicist Robin Bell, who is helping lead the project. "These flights are a unique opportunity to see through the ice, and address the question of why the ice sheets are changing."
"A remarkable change is happening on Earth, truly one of the biggest changes in environmental conditions since the end of the ice age," said Tom Wagner, cryosphere program scientist at NASA headquarters in Washington. "It's not an easy thing to observe, let alone predict what might happen next. Studies like this one are key."
Investigators from the University of Washington and University of Kansas will run their own suites of instruments.
Adapted from materials provided by The Earth Institute at Columbia University.

Lasers From Space Show Thinning Of Greenland And Antarctic Ice Sheets

The most comprehensive picture of the rapidly thinning glaciers along the coastline of both the Antarctic and Greenland ice sheets has been created using satellite lasers. The findings are an important step forward in the quest to make more accurate predictions for future sea level rise.

Reporting this week in the journal Nature, researchers from British Antarctic Survey and the University of Bristol describe how analysis of millions of NASA satellite measurements* from both of these vast ice sheets shows that the most profound ice loss is a result of glaciers speeding up where they flow into the sea.

The authors conclude that this 'dynamic thinning' of glaciers now reaches all latitudes in Greenland, has intensified on key Antarctic coastlines, is penetrating far into the ice sheets' interior and is spreading as ice shelves thin by ocean-driven melt. Ice shelf collapse has triggered particularly strong thinning that has endured for decades.

Lead author Dr Hamish Pritchard from British Antarctic Survey (BAS) says, "We were surprised to see such a strong pattern of thinning glaciers across such large areas of coastline – it's widespread and in some cases thinning extends hundreds of kilometres inland. We think that warm ocean currents reaching the coast and melting the glacier front is the most likely cause of faster glacier flow. This kind of ice loss is so poorly understood that it remains the most unpredictable part of future sea level rise."

The scientists compared the rates of change in elevation of both fast-flowing and slow-flowing ice. In Greenland for example they studied 111 fast-moving glaciers and found 81 thinning at rates twice that of slow-flowing ice at the same altitude.They found that ice loss from many glaciers in both Antarctica and Greenland is greater than the rate of snowfall further inland.

In Antarctica some of the fastest thinning glaciers are in West Antarctica (Amundsen Sea Embayment) where Pine Island Glacier and neighbouring Smith and Thwaites Glacier are thinning by up to 9 metres per year.

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Journal reference:

1. Hamish D. Pritchard, Robert J. Arthern, David G. Vaughan & Laura A. Edwards. Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets. Nature, 2009; DOI: 10.1038/nature08471

Adapted from materials provided by British Antarctic Survey.

Arctic Sea Ice Reaches Minimum Extent For 2009, Third Lowest Ever Recorded

The Arctic sea ice cover appears to have reached its minimum extent for the year, the third-lowest recorded since satellites began measuring sea ice extent in 1979, according to the University of Colorado at Boulder's National Snow and Ice Data Center.

While this year's September minimum extent was greater than each of the past two record-setting and near-record-setting low years, it is still significantly below the long-term average and well outside the range of natural climate variability, said NSIDC Research Scientist Walt Meier. Most scientists believe the shrinking Arctic sea ice is tied to warming temperatures caused by an increase in human-produced greenhouse gases being pumped into Earth's atmosphere.
Atmospheric circulation patterns helped the Arctic sea ice spread out in August to prevent another record-setting minimum, said Meier. But most of the 2009 September Arctic sea ice is thin first- or second-year ice, rather than thicker, multi-year ice that used to dominate the region, said Meier.
The minimum 2009 sea-ice extent is still about 620,000 square miles below the average minimum extent measured between 1979 and 2000 -- an area nearly equal to the size of Alaska, said Meier. "We are still seeing a downward trend that appears to be heading toward ice-free Arctic summers," Meier said.
CU-Boulder's NSIDC will provide more detailed information in early October with a full analysis of the 2009 Arctic ice conditions, including aspects of the melt season and conditions heading into the winter ice-growth season. The report will include graphics comparing 2009 to the long-term Arctic sea-ice record.
NSIDC is part of CU-Boulder's Cooperative Institute for Research in Environmental Sciences and is funded primarily by NASA.
Adapted from materials provided by University of Colorado at Boulder.