Scientists in Alaska say that new vegetation is spreading over the tundra as the climate gets warmer.
According to aerial photographs, the amount of greenery has doubled in some areas over the past 50 years.
The researchers suggest that new growth of shrubs and forest in the world's far northern regions could go some way towards offsetting the spread of deserts in the tropics.
But they warn that the Arctic regions cannot be expected to compensate for all the unpredictable effects of climate change.
Bleak landscape
When the north of Alaska was being explored for oil in the late 1940s, thousands of aerial photographs were taken of the bleak tundra north of the Arctic circle.
Cold-climate researchers from the United States' Army have now flown again over some of the locations to compare the extent of the the deciduous shrubs that grow there, beyond the northern limit of full-size trees.
In some cases, shrub cover of 10% had doubled since the first surveys.
"Our study area is in a location where human and natural disturbances are minimal," the researchers write in the scientific journal Nature, "so we attribute much of the increase in the abundance of shrubs to the recent change in climate".
The scientists say the extra biomass could absorb a significant amount of carbon dioxide - the most common greenhouse gas blamed for global warming.
'Unpredictable effects'
Studies of ancient peat deposits suggest that the same thing happened 8,000 years ago, at the end of the last ice age.
Even with the extra plants - which are too small to be valuable as timber - the region beyond Alaska's northernmost mountains could support few people.
If vegetation at lower latitudes, such as agricultural crops, also moves north in response to global warming, more farmland might be developed in areas that are now wilderness.
But the researchers stress that the Arctic regions cannot be expected to compensate for all the unpredictable effects of climate change.