The important thing is predicting whether this change will continue

Dr David Vaughan

Noting the confirmation this year by the Intergovernmental Panel on Climate Change (IPCC) of a global average warming of about 0.6 degrees Celsius during the 20th Century, they say this mean value "conceals the complexity of observed climate change".

"If the recent past is a guide to the future, regional climate changes will have more profound effects than the mean global warming suggests."

Trends in mean annual air temperature for 1950-98 show three areas of especially rapid regional warming: northwestern North America and the Beaufort Sea; an area around the Siberian plateau; and the Antarctic peninsula and the adjoining Bellingshausen Sea.

Upward trend

For all Antarctic stations, the mean temperature trend for 1959-96 is +1.2 degrees C per century, but there are marked regional variations.

Penguin colonies have moved as a result of the changes

At Amundsen-Scott base at the South Pole, annual air temperatures have actually cooled since 1958. On the Antarctic peninsula, though, they have warmed since reliable records began in the 1950s.

The BAS scientists say the longest records show a warming in the northwest of the peninsula "considerably larger than the mean Antarctic trend", with shorter records suggesting that the warming extends further south and east.

They say the importance of what has been happening is shown by its impact, with flowering plants extending their ranges, glaciers retreating and seasonal snow cover shrinking.

Penguins on the move

Penguin distribution is also changing. Adelie penguins, which need access to winter pack ice, are declining around Faraday. But chinstrap penguins, which usually need open water, are increasing.

The authors say three of the four ice cores from the peninsula show a rise in temperature over the last half-century.

And rapid regional warming has led to the loss of seven ice shelves during the last 50 years.

One, the Prince Gustav Channel shelf, disappeared in 1995, having come into existence 1900 years ago, when sedimentary cores show the climate was as warm as it has been recently.

'Exceptional' warming

The scientists say: "The recent rapid regional warming in the Antarctic peninsula is thus exceptional over several centuries, and probably unmatched for 1900 years.

"It may be tempting to cite anthropogenic greenhouse gases as the culprit, but to do so without offering a mechanism is superficial."

They suggest three possible mechanisms: changing ocean currents may have brought warmer deep water on to the continental shelf, reducing sea-ice; warmer air may have come into the region; or a unique sea-ice-atmosphere feedback may be at work.

Not knowing the cause of the changes so far, the authors say they cannot predict the future.

No predictions

But they describe what has happened as "a profound climatic change, an order of magnitude greater than global mean warming".

One of the authors, Dr David Vaughan, told BBC News Online: "The important thing is predicting whether this change will continue.

"What's stopping us is that we can't say which of these mechanisms is responsible.

"The climate modellers have done an astounding job in the last 10 years. But we now need to develop more sophisticated tools to enable us to predict regional climate changes."