The Northeast passage in the Arctic sea has remained closed to 'normal shipping' for all of recorded history....

Map of Arctic Sea

Northeast passage (8, purple) and Northwest Passage (2, yellow)

This year's opening marks the fourth time in five years that the Northeast Passage has opened to the extent that commercial shipping is able to traverse the route without assistance from icebreakers.

There has been commercial traffic using the route for many years with the assistance of icebreakers or if the ships themselves have specifically strengthened hulls.

The Passage trims 4,500 miles off the 12,500-mile trip through the Suez Canal, yielding considerable savings in fuel.

The Arctic sea ice is expected to continue to decline in the coming decades, shipping traffic through the Northeast Passage will likely become commonplace most summers.

The Passage has remained closed to navigation, except with assistance from icebreakers, from 1553 to 2005.

A new technique that examines organic compounds left behind in Arctic sediments by algae that live in sea ice give hope that a detailed record of sea ice extent going back to the end of the Ice Age 12,000 years ago may be possible.

Four of the five warmest decades in the past 2,000 years occurred between 1950 - 2000, despite the fact that summertime solar radiation in the Arctic has been steadily declining for the past 2,000 years.

Previous efforts to reconstruct past climate in the Arctic extended back only 400 years, so the new study--which used lake sediments, glacier ice cores, and tree rings to look at past climate back to the time of Christ, decade by decade-- is a major new milestone in our understanding of the Arctic climate.

The researchers found that Arctic temperatures steadily declined between 1 A.D. and 1900 A.D., as would be expected due to a 26,000-year cycle in Earth's orbit that brought less summer sunshine to the North Pole. Earth is now about 620,000 miles (1 million km) farther from the Sun in the Arctic summer than it was 2000 years ago.

However, temperatures in the Arctic began to rise around the year 1900, and are now 1.4°C (2.5°F) warmer than they should be, based on the amount of sunlight that is currently falling in the Arctic in summer.

"If it hadn't been for the increase in human-produced greenhouse gases, summer temperatures in the Arctic should have cooled gradually over the last century,” According to Bette Otto-Bliesner, a co-author from the National Center for Atmospheric Research.

The reduced melting in 2009 compared to 2007 and 2008 primarily resulted from a different atmospheric circulation pattern this summer. This pattern generated winds that transported ice toward the Siberian coast and discouraged export of ice out of the Arctic Ocean.

The previous two summers, the prevailing wind pattern acted to transport more ice out of the Arctic through Fram Strait, along the east side of Greenland.

As a result of this summer's melting, the Northeast Passage, a notoriously ice-choked sea route along the northern Russia, is now clear of ice and open for navigation. Satellite analyses by the University of Illinois Polar Research Group and the National Snow and Ice Data Center show that the last remaining ice blockage along the north coast of Russia melted in late August, allowing navigation from Europe to Alaska in ice-free waters.

Mariners have been attempting to sail the Northeast Passage since 1553, and it wasn't until the record-breaking Arctic sea-ice melt year of 2005 that the Northeast Passage opened for ice-free navigation for the first time in recorded history.

The fabled Northwest Passage through the Arctic waters of Canada has remained closed this summer, however.

An atmospheric pressure pattern set up in late July that created winds that pushed old, thick ice into several of the channels of the Northwest Passage.

Recent research by Stephen Howell at the University of Waterloo in Canada shows that whether the Northwest Passage clears depends less on how much melt occurs, and more on whether multi-year sea ice is pushed into the channels.

Counter-intuitively, as the ice cover thins, ice may flow more easily into the channels, preventing the Northwest Passage from regularly opening in coming decades, if the prevailing winds set up to blow ice into the channels of the Passage. The Northwest Passage opened for the first time in recorded history in 2007, and again in 2008. Mariners have been attempting to find a route through the Northwest Passage since 1497.

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