Arctic Sea Ice
Shrinks as Temperatures Rise
Despite cool temperatures in
August, summer sea ice falls below normal for fifth year
3 October 2006
This is a press release from
the National Snow and Ice Data Center (NSIDC), which is part of the Cooperative
Institute for Research in Environmental Sciences at the University of Colorado
at Boulder.
Media Relations Contacts:
Stephanie Renfrow, NSIDC: srenfrow@nsidc.org or +1 303 492-1497 (se habla Español)
Jim Scott, University of Colorado at Boulder: +1 303 492-3114
The year 2006 continues the
pattern of sharply decreasing Arctic sea ice, raising further concern that the
Arctic is responding to greenhouse warming. NSIDC Senior Research Scientist Mark
Serreze said, “If fairly cool and stormy conditions hadn’t appeared in
August, slowing the rate of summer ice loss, I feel certain that 2006 would have
surpassed last year’s record low for September sea ice.”
On September 14, the melting
season came to a close. On this day, known as the sea ice minimum, sea ice
covered 5.7 million square kilometers (2.2 million square miles) of the Arctic,
the fourth lowest of the twenty-nine-year satellite record for a single day. The
average sea ice extent for the entire month of September was 5.9 million square
kilometers (2.3 million square miles), the second lowest on record, missing the
2005 record by 340,000 square kilometers (131,000 square miles). Sea ice extent
is the sum of all regions where ice covers at least 15 percent of the ocean
surface.
Figure 1: September 2006 sea ice
extent. This image shows the average sea ice extent for the month of September;
the magenta line indicates the average September sea ice extent from 1979 to
2000. 2006 had the second-lowest average September sea ice extent on record.
This image is from the NSIDC Sea Ice Index
Figure 1 shows average ice extent
for September 2006; the magenta line indicates average September conditions over
the long-term record. In nearly all areas, sea ice retreated well north of where
it should have been in a typical September, continuing the pattern of dwindling
September sea ice.
Including 2006, the September
rate of sea ice decline is now approximately –8.59 percent per decade, or
60,421 square kilometers (23,328 square miles) per year. NSIDC Research
Scientist Julienne Stroeve said, “At this rate, the Arctic Ocean will have no
ice in September by the year 2060." The loss of summer sea ice does not
bode well for species like the polar bear, which depend on the ice for their
livelihood, she said.
Ice extent from January through
the middle of July 2006 was well below 2005 conditions, which, if it had
continued, would have led to a new record low. Figure 2 shows a timeline of sea
ice extent from June through October; the solid blue line that indicates 2006
trails beneath the dashed line of 2005 until mid-July.
Figure 2: Time series plot. 2006,
shown in solid blue, is below even the record year (2005), shown as a dashed
line, until mid-July, when sea ice conditions improved because of cooler Arctic
temperatures. However, 2006 was still well below the 1979 to 2000 average, shown
in solid gray. If the sea ice continues its slow rate of recovery, it will again
cross the 2005 line and set a new record low for October extent
The low sea ice through mid-July
was consistent with the very warm air temperatures that scientists were also
tracking in the Arctic (see Figure 3). Serreze said, “High temperatures over
the winter helped limit ice growth so that less ice formed. Much of the ice that
did grow was probably thinner than normal. Unusually high temperatures through
most of July then fostered rapid melt—a bad combination, as far as the sea ice
was concerned.”
Figure 3: Arctic
temperature anomalies. Average temperatures over most of the Arctic Ocean from
January through July 2006 were 1 to 4 degrees Celcius (2 to 7 degrees
Fahrenheit) above normal. The scale goes from red for temperatures strongly
above average to blue/purple for temperatures strongly below average. These
anomalies show temperatures compared to the average for 1968 to 1996. Dark blue
outlines indicate landmasses. Courtesy NOAA-CIRES Climate Diagnostics Center
However, air temperatures dipped
a bit lower in August. "August broke the Arctic heat wave and slowed the
melt, and storm conditions led to wind patterns that tend to spread the existing
ice over a larger area," Serreze said. Then, in September, temperatures
returned to the above-normal pattern. The warmer temperatures have meant a slow
recovery from the September minimum; the slow recovery of the sea ice is seen in
the flat line in Figure 2. At this rate, sea ice may set a new record, this time
for lowest October sea ice extent, Serreze said.
Another notable feature of the
2006 melt season was the development of a large polynya, or area of persistent
open water surrounded by sea ice, north of Alaska (see Figure 4). Research
scientist Walt Meier said that near its largest, in early September, the polynya
was the size of the state of Indiana. How the polynya formed is still not clear.
Unusual wind patterns may have forced the ice cover to spread apart. Scientists
also speculate that thin ice moved into the area over the winter, melting out
over the summer and creating the polynya. Another possibility is that warm
waters rose to the surface, helping melt the ice.
Figure 4: Beaufort Sea Polynya.
An unusual polynya, or area of persistent open water surrounded by ice, appeared
during the melt season. The polynya is the dark area of open water; to the left
is the coastline of Alaska, showing fall foliage color, and to the bottom right
is the North Pole. This image is from the Moderate Resolution Imaging
Spectroradiometer (MODIS) sensor, which flies on the NASA Terra and Aqua
satellites.
The team felt it would be
irresponsible to attribute the polynya to greenhouse warming. “However, as the
ice continues to thin with increasing climate warming, we may see features like
this more often,” Meier said.
NSIDC Lead Scientist Ted Scambos
added, “Arctic sea ice is an important climate indicator because it's so
sensitive to this initial warming trend.” As sea ice melts in response to
rising temperatures, it creates a positive feedback loop: melting ice means more
of the dark ocean is exposed, allowing it to absorb more of the sun’s energy,
further increasing air temperatures, ocean temperatures, and ice melt. The
observed changes in the ice cover indicate that this feedback is now starting to
take hold. Sea ice is only one indicator of Arctic change amongst many, such as
warming of permafrost, changing patterns of vegetation from tundra to shrubs, a
warming ocean, and accelerated melt of the Greenland ice sheet.
Given the especially steep
decline of sea ice since 2002 and the record low in September 2005, scientists
at NSIDC have been closely monitoring this year’s sea ice conditions, posting
new images and commentary in online updates throughout the end of the melt
season. NSIDC plans to continue to watch the sea ice and report on milestones in
the coming year.
“I’m not terribly optimistic
about the future of the ice,” Serreze said. “Although it would come as no
surprise to see some recovery of the sea ice in the next few years—such
fluctuations are part of natural variability—the long-term trend seems
increasingly clear. As greenhouse gases continue to rise, the Arctic will
continue to lose its ice. You can’t argue with the physics.”
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