Land within the Arctic circle is likely to experience explosive "greening" in the next few decades as grass, shrubs and trees thrive in soil stripped of ice and permafrost by global warming, a study said on Sunday.

Wooded areas in the Arctic could increase by as much as 52 percent by the 2050s as the so-called tree line -- the maximum latitude at which trees can grow -- shifts hundreds of kilometres (miles) north, according to computer simulations published in the journal Nature Climate Change.

"Such widespread redistribution of Arctic vegetation would have impacts that reverberate through the global ecosystem," said Richard Pearson of the American Museum of Natural History's Center for Biodiversity and Conservation.

The Arctic has become one of the world's 'hotspots' for global warming. Over the past quarter-century, temperatures there have been rising roughly twice as fast as in the rest of the world.

"These impacts would extend far beyond the Arctic region," Pearson said in a statement. "For example, some species of birds seasonally migrate from lower latitudes and rely on finding particular polar habitats, such as open space for ground-nesting."

In a separate study also published on Sunday, Dutch scientists said that iceshelves in Antarctica -- another source of worry in the climate equation -- have in fact been growing thanks to global warming.

Meltwater that runs off the Antarctic mainland provides a cold, protective "cap" for iceshelves because it comes from freshwater, which is denser than seawater, the team from the Royal Netherlands Meteorological Institute said.

Iceshelves are the floating blankets of ice that extend from the coast. They are fed by glaciers that move ice down from the icesheet and towards the sea.

The freshwater acts as a cold coating for the underside of the iceshelf, cocooning it from warmer seas, according to their study, appearing in the journal Nature Geoscience.

This would explain an apparent anomaly: why sea ice around Antarctica has been growing, reaching the greatest-ever recorded extent in 2010, it suggested.

Other scientists, asked to comment on the work, concurred that the phenomenon was one of several unexpected impacts from global warming, a hugely complex interplay of land, sea and air.

If confirmed, it does not detract from the broader trend -- and source of concern -- from warming, they said.

"This is a major, new piece of work with wide implications for assessing Antarctica's ice mass in the coming decades," said palaeo-climatologist Valerie Masson-Delmotte of France's Laboratory for Climate and Environmental Science (LCSE).

She pointed to a worrying rise in sea levels in 2011 and 2012, due partly to expansion of the ocean through warming and through glacier runoff, coming from mountains and also from Greenland and Antarctica, the two biggest sources of land ice on the planet.