The frozen continent: Hot and cold penguins

By SIMON COLLINS

It's getting too hot for the penguins in some parts of Antarctica. Scientists blame global warming for the disappearance of child-sized Adelie penguins from the northern tip of the Antarctic Peninsula, which stretches up towards South America, and for signs that the Adelies are migrating southwards in the Ross Sea south of New Zealand.

But the evidence of warming is patchy. Some parts of both the Antarctic and the Arctic are warming dramatically, sending an apparent warning to the rest of us. But other parts are getting colder.

At the Adelie colony on Cape Royds, 35km northwest of New Zealand's Scott Base, craggy, unshaven US penguin scientist David Ainley says penguins have moved up and down the Ross Sea as the climate changed over thousands of years.

He has looked south of the present colonies and found others that were occupied when the weather was warmer than it is today, 3000 to 4000 years ago.

In the colder times of the past 2000 years, when the sea south of Ross Island froze over all year round, Cape Royds on the southwest corner of the island became the penguins' southernmost colony.

In the late 1970s, it had only 1500 breeding pairs, a tiny fraction of the 135,000 pairs at Cape Crozier on the northeast end of the island.

But in the past 20 years, the numbers at Royds have more than doubled to about 4000 pairs in normal years, and at their peak growth in 1989, a few moved further south to reoccupy an old colony at Cape Barne, which had not been used for centuries.

"We think they are increasing because of global warming - loosening of the pack ice, making easier travelling," Dr Ainley says.

Average temperatures at Scott Base and nearby McMurdo Station have risen at an average rate of about 3C every 100 years since the two bases were established in 1957-58 - five times the average global warming of 0.6C during the 20th century.

At the Faraday and Vernadsky bases on the Antarctic Peninsula, the warming has been even more dramatic - an average increase of 5.7C in 100 years.

Adelie penguins have disappeared from the western coast of the peninsula, because the pack ice there has become so scarce that the penguins can no longer use it as a resting platform for their winter fishing.

Large pieces of the Larsen ice shelf, off the peninsula's east coast, broke off spectacularly in 1995 and 2002.

Yet temperatures at the US base at the South Pole have dropped at an average rate of 2C a century since 1958. The other major inland base, Vostok (Russia), has warmed at about the global average rate.

Weighing up the facts in the journal Climatic Change a few months ago, Dr David Vaughan and others concluded: "There is only weak evidence of significant overall warming in station data from continental Antarctica, and we find no evidence that this is significantly greater than the global mean."

The same patchiness shows up in the Arctic. Dr Craig Franklin, a Queensland-based, New Zealand-born expert on fish at both poles, says Arctic cod species have disappeared from the west coast of Greenland around the island of Disko, where temperatures have risen by "something like 4C in the last 15 to 20 years".


As he tells it, fish are adapted to a particular temperature. But unlike mammals, they take on the same temperature as the water they swim in, adjusting by processing their food faster at higher temperatures or when swimming faster - just as our hearts beat faster when we run.

"Fish at rest may have 20 beats a minute, and may increase to 40 beats a minute on exercise," Dr Franklin says.

"At 7C [the new temperature at Disko] those fish had a heart rate of 40 at rest, so there was no room for them to move.

"That's in the summer time. They do have seasonal changes in the water temperature, and in the winter they will be fine. But it's a huge concern."

The Greenland ice sheet is thinning, and the area of Arctic sea ice has shrunk by 5 per cent in the past 20 years.

In summer, ships can now sail through the fabled Northwest Passage over the top end of Canada.

Yet there has been little change in eastern Greenland, and the country cooled slightly on average during the 20th century.

The changes are happening so quickly that most scientists believe they are caused at least partly by human activities, such as the cars and industries which are increasing the amount of carbon dioxide in the air.

But clearly the effects are complex. A 2002 study by American scientists David Thompson and Susan Solomon, for instance, suggested that reduced ozone over Antarctica was changing wind patterns in a way which warms the Antarctic Peninsula and cools much of the rest of the continent.

Another US study found that mid-depth water in the circumpolar current flowing eastwards around Antarctica warmed by 0.17C in the past 50 years, about twice the rate of warming in the rest of the world's oceans. This may be warming coastal regions without yet affecting the interior.

Victoria University scientists Nancy Bertler, Alex Pyne and Matt Watson are looking for a better projection of the future through a better understanding of how the Antarctic climate has changed.

This summer, they have bored hundreds of metres into the ice on the Evans Piedmont Glacier and on Mt Erebus, studying the weight of snow in each year and the air trapped in the ice to work out past temperatures, humidity and storm frequencies.

Evidence from earlier drilling has shown that Antarctica has been much colder than at present and much warmer, with forests growing around its coasts.

Almost certainly, the polar regions are changing again in ways which could affect the climate of the whole planet. Exactly how will probably become clearer in the next few years.

* Tomorrow: Winter on ice