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 today.

It has long been known that the start of the Eocene was a 'thermal maximum', one of the hottest periods in Earthis history, and Antarctica would have been ice-free and much warmer than at present. But the new findings, based on sediment cores taken from the Antarctic seabed have enabled the first-ever detailed reconstruction of its environment and thus its climate.

This was previously impossible because any Eocene sediments remaining were destroyed by the subsequent glaciation or covered with ice. But pollen grains were washed, blown or transported by insects on to the shallow coastal shelf, where they were preserved in the mud for 50 million years.