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map with ice in white and land in gray
Figure 1. Arctic sea ice extent for September 2009 was 5.36 million square kilometers (2.07 million square miles), the third-lowest in the satellite record. The magenta line shows the median ice extent for September from 1979 to 2000. Sea Ice Index data. About the data.
—Credit: National Snow and Ice Data Center

6 October 2009

Arctic sea ice extent remains low; 2009 sees third-lowest mark

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 Contact: Katherine Leitzell, NSIDC: leitzell@nsidc.org or +1 303.492.1497

At the end of the Arctic summer, more ice cover remained this year than during the previous record-setting low years of 2007 and 2008. However, sea ice has not recovered to previous levels. September sea ice extent was the third lowest since the start of satellite records in 1979, and the past five years have seen the five lowest ice extents in the satellite record.

NSIDC Director and Senior Scientist Mark Serreze said, “It’s nice to see a little recovery over the past couple years, but there’s no reason to think that we’re headed back to conditions seen back in the 1970s. We still expect to see ice-free summers sometime in the next few decades.”

The average ice extent over the month of September, a reference comparison for climate studies, was 5.36 million square kilometers (2.07 million square miles) (Figure 1). This was 1.06 million square kilometers (409,000 square miles) greater than the record low for the month in 2007, and 690,000 square kilometers (266,000 square miles) greater than the second-lowest extent in 2008. However, ice extent was still 1.68 million square kilometers (649,000 square miles) below the 1979 to 2000 September average (Figure 2). Arctic sea ice is now declining at a rate of 11.2 percent per decade, relative to the 1979 to 2000 average (Figure 3).

Sea surface temperatures in the Arctic this season remained higher than normal, but slightly lower than the past two years, according to data from Mike Steele at the University of Washington in Seattle. The cooler conditions, which resulted largely from cloudy skies during late summer, slowed ice loss compared to the past two years (Figure 4). In addition, atmospheric patterns in August and September helped to spread out the ice pack, keeping extent higher. 

graph with extent on y axis and date on x axis
Figure 2. The updated time series plot puts this summer’s sea ice extent in context with other years. The solid light blue line indicates 2009; the dashed green line shows 2007; the dark blue line shows 2008, the light-green line shows 2005; the solid gray line indicates average extent from 1979 to 2000, and the gray area indicates the two standard deviation range of the data. Sea Ice Index data.
—Credit: National Snow and Ice Data Center

The ice cover remained thin, leaving the ice cover vulnerable to melt in coming summers. Scientists use satellites to measure ice age, a proxy for ice thickness. This year, younger (less than one year old), thinner ice, which is more vulnerable to melt, accounted for 49 percent of the ice cover at the end of summer. Second-year ice made up 32 percent, compared to 21 percent in 2007 and 9 percent in 2008 (Figure 5). Only 19 percent of the ice cover was over 2 years old, the least in the satellite record and far below the 1981-2000 average of 52 percent. Earlier this summer, NASA researcher Ron Kwok and colleagues from the University of Washington in Seattle published satellite data showing that ice thickness declined by 0.68 meters (2.2 feet) between 2004 and 2008.

NSIDC Scientist Walt Meier said, “We've preserved a fair amount of first-year ice and second-year ice after this summer compared to the past couple of years. If this ice remains in the Arctic through the winter, it will thicken, which gives some hope of stabilizing the ice cover over the next few years. However, the ice is still much younger and thinner than it was in the 1980s, leaving it vulnerable to melt during the summer.”

Arctic sea ice follows an annual cycle of melting and refreezing, melting through the warm summer months and refreezing in the winter. Sea ice reflects sunlight, keeping the Arctic region cool and moderating global climate. While Arctic sea ice extent varies from year to year because of changeable atmospheric conditions, ice extent has shown a dramatic overall decline over the past thirty years. During this time, ice extent has declined at a rate of 11.2 percent per decade during September (relative to the 1979 to 2000 average) (Figure 6), and about 3 percent per decade in the winter months.

graph with monthly trend line
Figure 3. September ice extent from 1979 to 2009 shows a continued decline. The September rate of sea ice decline since 1979 has now increased to 11.2 percent per decade. Sea Ice Index data.
—Credit: National Snow and Ice Data Center

NSIDC Lead Scientist Ted Scambos said, “A lot of people are going to look at that graph of ice extent and think that we've turned the corner on climate change. But the underlying conditions are still very worrisome.”

Reference:
Kwok, R., and D. A. Rothrock. 2009. Decline in Arctic sea ice thickness from submarine and ICESat records: 1958–2008, Geophys. Res. Lett., 36, L15501, doi:10.1029/2009GL039035.

For a full listing of press resources concerning Arctic sea ice, including previous press releases and quick facts about why and how scientists study sea ice, please see "Press Resources" on the NSIDC Arctic Sea Ice News & Analysis Web page (http://nsidc.org/arcticseaicenews/).

 

 

maps of 2007, 08, and 09 with arctic ocean temps in colors
Figure 4. A comparison of sea surface temperatures and anomalies shows that the Arctic Ocean was warmer this year than the 1982 to 2006 average, but cooler than the past two years. Cooler temperatures in 2009, compared to 2007 and 2008, helped prevent another year of record ice low.
—Credit: National Snow and Ice Data Center courtesy Mike Steele, University of Washington

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ice age figure
Figure 5. These images compare ice age, a proxy for ice thickness, in 2007, 2008, 2009, and the 1981 to 2000 average. This year saw an increase in second-year ice (in blue) over 2008. At the end of summer 2009, 32 percent of the ice cover was second-year ice. Three-year and older ice were 19 percent of the total ice cover, the lowest in the satellite record.
—Credit: National Snow and Ice Data Center courtesy C. Fowler and J. Maslanik, University of Colorado at Boulder
two globes side by side with sea ice extent. click for animation
Figure 6: A time series of images shows the decline in September sea ice extent over the thirty-year satellite record. Click on the image to open the animated time series in a new window. At left, an animated time series shows ice extent for each of the past thirty Septembers, 1979 to 2009; for comparison, the right-hand image shows September 2009. Ice extent this fall was the third-lowest in the satellite record.
Click to view animation (1.1 MB)
—Credit: National Snow and Ice Data Center/NASA Earth Observatory