Since the start of the satellite record in 1979, scientists have observed the continued disappearance of older "multiyear" sea ice that survives more than one summer melt season. Some scientists suspected that this loss was due entirely to wind pushing the ice out of the
Wednesday, November 17, 2010
Measuring Arctic Ice Melt
The big story is that the
Arctic has lost 97% of its long term ice over the past thirty years and now retains a mere 22000 square miles of the stuff. This confirms everything I have been saying since 2007 when I stated that decline would complete during 2011 and 2012. The long term ice is gone for all intents and purposes and the last season ice and its ilk will easily fall apart. It is breakup time in the Arctic.
Stroeve has not understood it either. The
Arctic is now entering crash mode. These numbers merely confirm it. Wind and wave can now easily accelerate the melt and promote a warming of the surface waters. This will continue to postpone slightly the onset of the first freeze at summer’s end.
I have also added a report from NASA’s group which is also saying the same thing through a pixel counting scheme.
At least we now have real numbers to attach to our observations of years past.
Measuring fast-melting Arctic sea ice
BY Seth Shulman
15 NOV 2010 10:55 AM
You've probably seen pictures of stranded polar bears and heard that global warming is causing the melting of Arctic sea ice -- that is, floating ice formed from freezing ocean surface water. But you may imagine, as most people do, that this distant phenomenon is unfolding gradually over a centuries-long time frame.
Julienne Stroeve, a climate scientist at the National Snow and
Ice Data Center in , has compiled detailed measurements that melt away any such misconceptions. Stroeve is closely monitoring the extent of Arctic sea ice, and her research shows that dramatic changes are occurring right now -- far faster than most experts anticipated and with enormous consequences for the whole planet, not just the Arctic region. Boulder, Colo.
For instance, during the warmest part of 2010, the total amount of Arctic sea ice -- the so-called "seasonal minimum" -- was the third-smallest ever recorded. The smallest and second-smallest seasonal minimums were measured in 2007 and 2008, respectively. Natural variability, including factors like cloud cover, can easily explain differences in melting from year to year, Stroeve notes. But the big news is that the smallest amounts of Arctic sea ice ever measured have all occurred in recent years. "Basically, ever since 2002, we've had one pronounced record minimum after another," she says. "The data all point to a strong warming signal."
Stroeve explains that highly reliable data on the extent of Arctic sea ice has been collected since 1978. From then until now, she has found clear evidence of a 30-year melting trend, which, she says, "cannot be easily explained away by natural variability." But her work is even more notable for its findings about the speed of the change. Over this same 30 years, a relatively brief period, Stroeve has found that some 40 percent of the region's summer (or more precisely, September) ice has melted.
The fast pace of melting is seen even more dramatically, she explains, when one considers the age of the Arctic ice. Many parts of the
Arctic Ocean freeze each year during the coldest months. But only ice that lasts throughout the year gradually becomes thicker over the course of consecutive seasons. "In the 1980s, the Arctic contained roughly 386,000 square miles of ice that was determined to be at least five years old," she says. Now, "at the end of the melt season in September, only 22,000 square miles of such older, thicker ice remains." In other words, the region has already lost more than 97 percent of the thicker year-round ice that existed just three decades ago. As she explains, "all the climatic processes seem to be pushing rapidly toward a seasonally ice-free Arctic Ocean."
Stroeve says that initially she was as surprised by the data as anyone else. "I didn't think global warming was even happening in the early 1990s when I began this work," she says. Back then, some climate models were projecting that carbon emissions would lead to a pronounced warming trend at the poles. But Stroeve was always more interested in actual measurements than in climate modeling. "I think I was lured into studying the poles by the prospect of adventurous fieldwork in Greenland or the
Alps," she says with a laugh.
The daughter of an aerospace engineer, Stroeve had always exhibited a strong aptitude for math and science and an adventuresome spirit. From childhood through her high school years, her dream was to be an astronaut, she says, and she might have continued on that track if she hadn't realized that her susceptibility to motion sickness was a serious impediment to working in space.
Her love of adventure continues in her work today, in which she makes regular research trips to the Arctic and
Greenland to measure ice thickness and other snow and ice measurements. It might not be space travel, but Stroeve says her fieldwork has been as exciting as she could have hoped. "When I first visited Greenland, it was the most stunning landscape I had ever seen," she says.
Along with her research in the polar regions, much of the data Stroeve analyzes comes from satellites that detect passive microwave radiation. As she explains, the higher brightness of ice in the microwave part of the spectrum can be seen by satellites even through cloud cover. "In the often-cloudy polar regions, that makes it an incredibly useful tool, providing data in which we have a high degree of confidence," she says. These detailed satellite measurements of Arctic sea ice led Stroeve to shed her initial doubts about global warming. "My views changed as I studied the emerging data," she says. "With record low sea-ice extents year after year, it became clear that a significant warming trend was underway."
Looking closely at the data, Stroeve realized that a phenomenon called Arctic amplification, a form of positive feedback, is accelerating the warming trend, causing it to occur many years sooner than most climate models had projected. Arctic amplification occurs primarily because water absorbs far more heat than ice does. On average, Stroeve explains, water absorbs almost 93 percent of all the incoming solar radiation, whereas the white surface of snow-covered ice reflects about 80 percent of incoming solar radiation back into space.
As more and more of the
Arctic Ocean sea ice melts over the summer months, it hastens further warming, Stroeve explains. She and her colleagues at the National Snow and have measured the effect, showing that in areas where summer ice has disappeared, local autumn air temperatures have been more than 5 degrees F higher than the long-term average. Ice Data Center
The potential of such feedbacks to cause abrupt climate change as the
Arctic Ocean becomes nearly ice-free in the warm season drew widespread attention to Stroeve's work in 2007. In that record-breaking warm year, the Arctic Ocean lost more than one-quarter of its remaining ice. "Because new ice can't get very thick in one season, it is more vulnerable to annual temperature changes, as we saw in 2007," she says.
The possibility of sudden shifts in the region's climate, and thus the planet's climate, is the most frightening implication of her research, Stroeve says. The quick and volatile changes in Arctic sea ice remind us that the geological record contains clear evidence of abrupt climatic changes in the planet's history. "We know that Arctic ice has historically helped keep the Northern Hemisphere cool," Stroeve says. "Without it, given atmospheric circulation, the planet will certainly warm more quickly. But we don't know enough about the system to fully project how swift the changes might turn out to be."
The prospect of sudden climate change is certainly scary, Stroeve says. But she adds that, because the stakes are so high, her decision to study Arctic sea ice has proven a more exciting choice than she ever imagined. As she puts it, "Not a lot of people were looking at sea ice when I began my research. But especially after 2007, which took everyone by surprise, it has become something that climate scientists are intensely interested to know about."
This is the fifteenth installment of
's Climate Scientists: A series from the Union of Concerned Scientists. Click here to read all the climate scientist profiles. America
Union of Concerned Scientists is currently leading a campaign to elevate the voices of climate scientists and educate the public about the overwhelming scientific evidence for human-caused global warming. Learn how you can get involved at www.ucsusa.org/evidence.
Seth Shulman has worked for more than 25 years as a writer and editor specializing in issues in science, technology and the environment. A graduate of Harvard University, he has written five books and hundreds of articles for magazines including Smithsonian, The Atlantic, Parade, Discover, Rolling Stone, Popular Science, The Chronicle of Higher Education, The Progressive, and Time, and for newspapers including the Times of London, The Boston Globe, and The Los Angeles Times.
NASA Study Quantifies Role Of Melt In Loss Of
Ice Old Arctic Sea
by Staff Writers
A NASA analysis of satellite data quantified for the first time the amount of older and thicker "multiyear" sea ice lost from the
Arctic through melt. A mosaic of satellite images show the movement of fragmented ice away from ice edge, which scientists use to track the loss of multiyear ice due to melt. Credit: NASA Earth Observatory. Full size image
In this study, Ron Kwok and Glenn Cunningham at NASA's Jet Propulsion Laboratory in
Pasadena, Calif., used a suite of satellite data to clarify the relative role of export versus melt within the Arctic Ocean.
Kwok and Cunningham show that between 1993 and 2009, a significant amount of multiyear ice - 1,400 cubic kilometers (336 cubic miles - was lost due to melt, not export. "The paper shows that there is indeed melt of old ice within the Arctic basin and the melt area has been increasing over the past several years," Kwok said. "The story is always more complicated - there is melt as well as export - but this is a another step in calculating the mass and area balance of the Arctic ice cover."
The results have implications for understanding how Arctic sea ice gets redistributed, where melt occurs in the
Arctic Ocean and how the ocean, ice and atmosphere interact as a system to affect Earth's climate. The study was published October 2010 in Geophysical Research Letters.
Scientists track the annual cycle of Arctic sea ice coverage as it melts through the summer to reach a minimum extent each September, before refreezing through fall and winter. Much of that ice is seasonal, meaning that it forms and melts within the year.
But multiyear ice that survives more than one season has also been declining, as noted in previous work by Joey Comiso of NASA's Goddard Space Flight Center in Greenbelt, Md., who shows a loss of about 10 percent per decade since the beginning of the satellite record in 1979. Scientists want to know where this loss is occurring.
"The decline of the multiyear ice cover of the last several decades has not been quantitatively explained," Kwok said.
To investigate the loss of multiyear ice, Kwok and Cunningham looked at a 17-year span of data from 1993 to 2009 from a range of polar-observing satellites and instruments including NASA's Quick Scatterometer (QuikScat); the Ice, Cloud and land Elevation Satellite (ICESat); the Advanced Microwave Scanning Radiometer (AMSR); and the European Space Agency's ERS-1 and ERS-2. Some instruments track ice coverage, while others track motion and concentration.
The team collected satellite images and tracked pixels of multiyear ice from April 1, prior to the onset of seasonal melt, and into the summer. Pixels that deviate away from images of the ice edge were considered lost to melt.
The team compared summertime melt of multiyear ice in the Beaufort Sea with estimates of ice lost from the Arctic basin through
Fram Strait - a major passage through which ice can exit the Arctic Ocean. The comparison revealed how much multiyear ice was lost to export and how much was lost to melt.
They found that over the 17-year period, an area of 947,000 square kilometers (365,639 square miles), or about 32 percent of the decline in multiyear sea ice area, was lost in the Beaufort Sea due to melt.
A similar calculation using thickness estimates from NASA's ICESat from 2004 to 2009 show a volume loss of 1,400 cubic kilometers (336 cubic miles), or about 20 percent of the total loss by volume.
How and where multiyear ice is lost has impacts on the Arctic system. For example, more loss by melt means more freshwater remains in local Arctic waters rather than being transported southward.
"These results also show that thick multiyear sea ice is not immune to melt in the Pacific sector of the
Arctic Ocean in today's climate," Kwok said.
The additional freshwater from melt in the Pacific sector, which encompasses the area of study, could contribute to the freshening of the Beaufort Gyre and potentially influence circulation, but the degree of that influence remains uncertain.
Not all of the multiyear ice loss is accounted for, however. Ice loss through
and from melt from 2005 to 2008 accounts for just 52 percent of total ice loss. The team suggests that melt in other Arctic regions and outflow through other passages besides Fram Strait could account for the difference. Fram Strait