Global warming could be accelerated by an increase of plant cover in the arctic region, according to research published in the Journal of Geophysical Research-Biogeosciences.

The arctic region is already warming more quickly than anywhere else on Earth, and higher temperatures have stimulated winter plant growth on the tundra. This additional vegetation could increase the amount of solar energy absorbed in the region (snow reflects much of this energy straight back into space) by as much as 70 per cent, the researchers say.

The study, carried out by US Army Cold Regions Research and Engineering Laboratory and at Colorado State University, looked at how an increase in plant cover in high latitudes, particularly in Alaska, impacts the Earth's albedo - a measure of how much sunlight is reflected from the planet's surface.

"Basically, if tundra is converted to shrubland, more solar energy will be absorbed in the winter than before," says Matthew Sturm, lead author of the study.

He notes that the regional warming, and the subsequent increase in plant cover will quickly form a positive feedback loop. This could accelerate increases in the shrubs' range and size over the four million square kilometer tundra, and cause significant changes in the region.

The researchers studied five sites in subarctic Alaska, each with a different kind of plant cover - ranging from full forest canopy, through to barren tundra. They measured the mid-winter albedo of each site and found that melting began sooner in areas covered in shrubs than on the snowy plains.

Conversely, the shrubby areas had more shade, so the rate of melting was slower overall. The thaw in all five regions finished at approximately the same time, the researchers found.

Sturm concludes that the changes would undoubtedly affect the carbon budget in the region, but added that scientists don't yet understand exactly how. One thing he is sure of is that with an estimated 40 per cent of the world's carbon currently holed up in arctic soils, any change to the arctic's carbon balance would certainly have a knock on effect on the global climate. ®