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Warmer air, soil temperatures are driving greening in the Arctic

More than a third of Arctic tundra has experienced greening over the last few decades. Photo by Logan Berner/Northern Arizona University
More than a third of Arctic tundra has experienced greening over the last few decades. Photo by Logan Berner/Northern Arizona University

Sept. 23 (UPI) -- New data, collected and analyzed by scientists with NASA and the U.S. Geological Survey, suggests rising air and soil temperatures are accelerating plant growth across tundra ecosystems, causing much of the Arctic to green, according to a study published this week in the journal Nature Communications.

"The Arctic tundra is one of the coldest biomes on Earth, and it's also one of the most rapidly warming," lead researcher Logan Berner said in a news release.

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"This Arctic greening we see is really a bellwether of global climatic change -- it's a biome-scale response to rising air temperatures," said Berner, a global change ecologist with Northern Arizona University in Flagstaff.

Greening can encompass new colonization by tundra grasses or by already present grasses becoming thicker. The phenomenon can also involve the encroachment of shrubs into acreage typically dominated by grasses and moss.

To measure greening trends, researchers used images collected by NASA's Landsat spacecraft. The satellites have been imaging tundra across Alaska, Canada and western Eurasia for the past several decades.

"Landsat is key for these kinds of measurements because it gathers data on a much finer scale than what was previously used," said Scott Goetz, a professor at Northern Arizona University.

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Using computer algorithms, researchers randomly selected plots to measure greening trends. They found more 38 percent of the plots imaged between 1985 and 2016 showed evidence of greening, and just 3 percent showed signs of declining plant growth, or browning.

Beginning in 2000, Landsat craft also began imaging eastern Eurasian tundra sites. Analysis showed 22 percent of eastern Eurasian tundra sites have greened over the last two decades, while 4 percent showed signs of browning.

"Whether it's since 1985 or 2000, we see this greening of the Arctic evident in the Landsat record," Berner said. "And we see this biome-scale greening at the same time and over the same period as we see really rapid increases in summer air temperatures."

Researchers used climate data as well as measurements made in field study sites in the Arctic to provide context for their new analysis.

The research confirms that in addition to rising air temperatures, greening trends were associated warming soil temperatures, as well as higher soil moisture, the scientists said.

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