Trees and shrubs are taking hold on what was once tundra, like this young pine and surrounding shrubs in Norway's Arctic Finnmark.Hans Tommervik of NINA, Norway

As the planet warms, the Arctic is feeling the heat. Trees and shrubs are taking hold on what was once tundra, like this young pine and surrounding shrubs in Norway's Arctic Finnmark.

A new international study of the satellite record of greening landscape shows that the places which were firmly Arctic in climate during the mid-20th century are now transforming into evergreen forest lands. If the trend continues, by the end of this century northern Sweden could get the temperatures more common to southern France and northernmost Canada could be more like Montana.

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NASA Vegetation IndexNASA's Goddard Space Flight Center Scientific Visualization Studio

The greening trend can be seen in plant growth over about 21 million square kilometers of boreal (pine forest) and Arctic regions during the past thirty years. The data for this map comes from the newly produced NASA Vegetation Index. The same satellite data was used by an international team of 21 scientists from seven countries in a paper published on March 10 in the journal Nature Climate Change.

“As a result of the enhanced warming...the total amount of heat available for plant growth in these northern latitudes is increasing,” said Compton Tucker, climate scientist at NASA’s Goddard Space Flight Center. “This created during the past 30 years large patches of vigorously productive vegetation, totaling more than a third of the northern landscape — over 9 million square kilometers, which is roughly about the area of the USA — resembling the vegetation that occurs further to the south.”

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Northern Siberian foothills. Bruce Forbes of The Arctic Centre, University of Lapland, Finland

The changes are not only seen from space, but on the ground. Shrubs are making vigorous headway in northwest Siberia at the northernmost foothills of the Ural Mountains on Russia's Yamal Peninsula.

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Russia's Altai Mountains.Sergey Kirpotin, Tomsk State University & Terry Callaghan - EU-Interact

The march of the trees can also be seen in tundra beyond the Arctic. In mountains high altitude creates Arctic conditions. But in places like Russia's Altai Mountains, near Mongolia, the trees are advancing as the mountain glaciers retreat.

More heat without more water makes for a drier climate.Ranga Myneni/ Boston University

The researchers also looked at what is likely to happen in the future using 17 of the world's most sophisticated computer climate models. They found that by the end of this century, places like Victoria Island in northern Canada will have temperatures more like mid-20th century Montana while in Europe, Arctic Sweden's temps will resemble those of Southern France in the mid-20th century.

“In principle, you should be able to grow grapes in Sweden,” said Boston University vegetation and climate researcher Ranga Myneni. “A lot of people think this is helping the plants,” but at what point do you stop? he asked. Too much warming in the Arctic and in areas to the south could create new climate problems. For instance, so far the warming in northern North America has not been accompanied by more precipitation (as it has in northern Eurasia), Myneni explained. More heat without more water makes for a drier climate. Myneni is also the scientist behind a new global petition to take action on climate change.