When Antarctica was a tropical paradise

Antarctica is the coldest, most desolate place on Earth, a land of barren mountains buried beneath a two-mile thick ice cap. Freezing winds batter its shores while week-long blizzards frequently sweep its glaciers.

Yet this icy vision turns out to be exceptional. For most of the past 100 million years, the south pole was a tropical paradise, it transpires.

"It was a green beautiful place," said Prof Jane Francis, of Leeds University's School of Earth and Environment. "Lots of furry mammals including possums and beavers lived there. The weather was tropical. It is only in the recent geological past that it got so cold."

Prof Francis was speaking last week at the International Symposium on Antarctic Earth Sciences in Edinburgh. More than 500 polar researchers gathered to discuss the latest details of their studies, research that has disturbing implications for the planet's future. Drilling projects and satellite surveys show the whole world, not just Antarctica, was affected by temperature rises and that these were linked, closely, to fluctuations in levels of carbon dioxide in the atmosphere.

"Fifty five million years ago, there were more than 1,000 parts per million (ppm) of carbon dioxide in the atmosphere," said Professor Stephen Pekar, of City University of New York. "That heated the world enough to melt all its ice caps. Sea levels would have been almost 200ft higher than today. "

At present, there are 390ppm of CO₂ in the atmosphere, a rise – caused by emissions from power plants, factories and lorries – from preindustrial levels of around 280ppm. This has already raised global temperatures by almost 1C. At its present rate of increase – around 2ppm a year - it will still take a long time to reach 1,000ppm.

But we should take little comfort from that, added Pekar. "By the time we get to 500ppm we will start to see major melting of the ice caps."

Measurements taken by Henk Brinkhus and Peter Bijl of Utrecht University as part of the International Ocean Drilling Programme were revealed at the symposium. A kilometre under the seabed at Wilkes Land in east Antarctica, they found sediments containing the pollen of plants that only thrive in the tropics today. "We have found the same kind of material, from the same period, in the Arctic as well. These show the poles were just as warm as lands at the equator," said Brinkhus. "Carbon dioxide turned the planet into a uniformly warm hothouse."

Understanding exactly why our atmosphere went through such extreme fluctuations in CO₂ is now a pressing concern for scientists. Most hypotheses suggest that at certain times, movements of tectonic plates caused carbonate-rich rocks and sediments to release their CO₂. The world heated up. Then, in intervening periods, that CO₂was absorbed by a range of natural processes and the world cooled down again.

"We now know that over geological time, carbon dioxide levels and atmospheric temperatures are interlinked," added Brinkhus. "When the former rises, the latter goes up in its wake. These changes took place over millions of years. However, we are now making similar changes in decades and have little chance to adjust. There are bad days ahead for the planet."

This point was backed by Pekar. "When we look at the Antarctic's past, we get a vision of what our planet might be like in a couple of hundred years: a hot, drowned world. "