Shrinking Arctic Sea Ice Opens Northwest Passage

BOULDER, Colorado, October 1, 2007 (ENS) - Arctic sea ice during the 2007 melt season sank to the lowest levels since satellite measurements began in 1979, according to a report released today by the National Snow and Ice Data Center. The Arctic sea ice receded so much that the Northwest Passage completely opened for the first time in human memory.

This year's low was nearly 25 percent less than the previous low set in 2005.

NSIDC Senior Scientist Mark Serreze said, "The sea ice cover is in a downward spiral and may have passed the point of no return. As the years go by, we are losing more and more ice in summer, and growing back less and less ice in winter. We may well see an ice-free Arctic Ocean in summer within our lifetimes." NSIDC scientists agree that this could occur by 2030.

This image compares the average sea ice extent for September 2007, on the left, to September 2005. The magenta line indicates the long-term median from 1979 to 2000. (Image courtesy NSIDC)

If ship and aircraft records from before the satellite era are taken into account, the NSIDC scientists say, Arctic sea ice may have fallen by as much as 50 percent from the 1950s.

"While a number of natural factors have certainly contributed to the overall decline in sea ice, the effects of greenhouse warming are now coming through loud and clear," Serreze said. "The implications for global climate, as well as Arctic animals and people, are disturbing."

Changes in sea ice extent, timing, ice thickness, and seasonal fluctuations are already having an impact on the people, plants, and animals that live in the Arctic.

NSIDC research scientist and Arctic resident Shari Gearheard said, "Local people who live in the region are noticing the changes in sea ice. The earlier break up and later freeze up affect when and where people can go hunting, as well as safety for travel."

Arctic sea ice reached its lowest annual extent - the absolute minimum - on September 15, 2007.

The average sea ice extent for the month of September was 1.65 million square miles (4.28 million square kilometers), the lowest September on record, shattering the previous record for the month, set in 2005, by 23 percent.

At the end of the melt season, September 2007 sea ice was 39 percent below the long-term average from 1979 to 2000.

September ice extent from 1979 to 2007 shows a steep decline. (Graph courtesy NSIDC)

NSIDC scientists monitor and study Arctic sea ice year round, analyzing satellite data to understand the observations of regional changes and complex feedbacks.

One factor that contributed to this fall's extreme decline was that the ice was entering the melt season in an already weakened state. NSIDC research scientist Julienne Stroeve said, "The spring of 2007 started out with less ice than normal, as well as thinner ice. Thinner ice takes less energy to melt than thicker ice, so the stage was set for low levels of sea ice this summer."

Another factor that accelerated the ice loss this summer was an unusual atmospheric pattern, with persistent high atmospheric pressures over the central Arctic Ocean and lower pressures over Siberia.

The scientists noted that skies were fairly clear under the high-pressure cell, promoting strong melt. At the same time, the pattern of winds pumped warm air into the region. While the warm winds fostered further melt, they also helped push ice away from the Siberian shore.

NSIDC research scientist Walt Meier said, "While the decline of the ice started out fairly slowly in spring and early summer, it accelerated rapidly in July. By mid-August, we had already shattered all previous records for ice extent."

Compiled from satellite data, this image shows September 14, 2007 sea ice minimum record (Image courtesy NSIDC)

The Northwest Passage that presented a great barrier to early 20th century explorers, was completely open this melt season.

Explorers and other seafarers had long recognized that this passage, through the straits of the Canadian Arctic Archipelago, represented a potential shortcut from the Pacific to the Atlantic.

Roald Amundsen began the first successful navigation of the route starting in 1903. It took his group two-and-a-half years to leapfrog through narrow passages of open water, with their ship locked in the frozen ice through two cold, dark winters. More recently, icebreakers and ice-strengthened ships have on occasion traversed the normally ice-choked route.

But by the end of the 2007 melt season, a standard ocean-going vessel could have sailed smoothly through.

On the other hand, the Northern Sea Route, a shortcut along the Eurasian coast that is often at least partially open, was completely blocked by a band of ice this year.

In addition to the record-breaking retreat of sea ice, NSIDC scientists also noted that the date of the lowest sea ice extent, or the absolute minimum, has shifted to later in the year. This year, the five-day running minimum occurred on September 16, 2007; from 1979 to 2000, the minimum usually occurred on September 12.

NSIDC Senior Scientist Ted Scambos said, "What we've seen this year fits the profile of lengthening melt seasons, which is no surprise. As the system warms up, spring melt will tend to come earlier and autumn freezing will begin later."

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