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Shrub census shows Alaskan Arctic losing its cool

Advancing shrubs could herald warming temperatures in Alaska
Advancing shrubs could herald warming temperatures in Alaska  

(CNN) -- Aerial pictures show small trees in the Alaskan tundra have bulked up in size and number in recent decades, a find that lends support to the widespread scientific view that the Arctic expanse is steadily warming.

Climate patterns elsewhere could be influenced by the trend in the Alaskan Arctic, which has served as an important sink for global carbon in the past, researchers said Wednesday.

A hinterland of mountains and plains, grass, snow and ice, broken up by the occasional stand of small hardy trees, the remote region has gradually warmed since about 1850, capped with an accelerated rise over the last three decades, scientists have theorized.


Experimental models suggest a burst of shrub growth should have accompanied the temperature rise. Government geophysicists said they now found direct evidence of it, having pored over aerial pictures that document changes in the ground cover over the past 50 years.

"We found distinctive, and in some cases, dramatic increases in the height and diameter of individual shrubs," wrote geophysicist Matthew Sturm and colleagues in the May 31 edition of the journal Nature.

The research team found growth increases in 36 of 66 study locations. In some cases the shrub cover doubled. It stayed the same in 30 places. Nowhere did it retreat. Alder trees lead the growth advance, followed by birch and willow.

The tundra transformation took place in a pristine stretch between the Brooks Range and the Arctic coast, marked by few human or natural disturbances.

"So we attribute much of the increase in the abundance of shrubs to the recent change in climate," wrote Sturm and his associates, who work for the U.S. Army Cold Regions Research & Engineering Laboratory and the University of Alaska-Fairbanks.

The rising tree population could disrupt the natural processes that cycle snow and energy through the region and increase the amount of carbon it stores, according to the researchers.

Scientists presume that carbon sinks can slow the effects of global warming by trapping the main greenhouse gas, carbon dioxide. But the net effect of the changing Alaskan Arctic on world climate remains unknown.

"When you increase the shrub cover you trap more snow, which keeps the soil warmer," said Sturm, calling by cellphone 70 miles east of Nome, Alaska, in a small village that serves as his base to study seasonal snow changes. "We're not sure how the trend will go."

• Cold Regions Research and Engineering Laboratory

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