Palm trees could grow in the Antarctic if climate change continues unabated, new research has shown - just as they did 55 million years ago.
A study has found that similar trees grew in the region during the early Eocene epoch, when the area had a near-tropical climate with frost-free winters, even in the polar darkness. Global levels of the principal greenhouse gas, carbon dioxide, were nearly three times as high then as now.
It has long been known that the start of the Eocene was a "thermal maximum", one of the hottest periods in Earth's history, and that Antarctica as a continent would have been ice-free and much warmer than at present.
But the new findings, based on sediment cores taken from the Antarctic seabed and disclosed yesterday in the journal Nature, have enabled the first-ever detailed reconstruction of its environment and thus its climate.
This was previously impossible because any Eocene sediments remaining on land were destroyed by the subsequent glaciation of Antarctica, or covered with thousands of feet of ice. But pollen grains were washed, blown or transported by insects on to the shallow coastal shelf, where they settled in the mud and were preserved for 50 million years.
Analysis of the pollen in the sediment reveals two plant environments, one being a lowland, coastal warm rainforest similar to that in northern Australia or New Guinea, dominated by palms, tree-ferns and members of the Bombacoideae family, which include the famous baobabs of Africa.
The other was an upland, mountain forest region, further into the continent's interior, with beech trees and conifers.
The presence of the plants indicates that temperatures on the Antarctic coast were around 16C and summers reached 21C. Antarctica was in nearly the same position it now is, over the South Pole, so the winter months would have been dark, like now, but the presence of the flora indicates it was warmer than 10C year round.
The study was done by a team of 36 scientists involved in the Integrated Ocean Drilling Research Programme, a project set up to research the early Eocene climate.