The South Pole, the most isolated part of the planet, is also one of the most rapidly heated, scientists said on Monday, with surface air temperatures rising since the 1990s at a rate three times faster than average global.
While warming may be the result of natural climate change alone, the researchers said, it is likely that the effects of man-made warming contributed to this.
The post, home of United States research base in the high, cold void of the interior of Antarctica, heated to about 0.6 degrees Celsius or 1.1 degrees Fahrenheit, per decade for the past 30 years, the researchers reported in a article published in Nature Climate Change. The global average in that period was around 0.2 degrees Celsius per decade.
Although parts of coastal Antarctica are losing ice, which contributes to rising sea levels, the pole is not at risk of melting, as the average temperature throughout the year is still minus 50 degrees Celsius. But the discovery shows that nowhere is affected by changes on a warming planet.
Analyzing weather data and using climate models, the researchers found that the rise in temperature is a result of changes in atmospheric circulation that have their origins thousands of miles away in the western tropical Pacific Ocean.
“The South Pole is heating up at an incredible rate and is mainly driven by the tropics,” said Kyle R. Clem, a postdoctoral researcher at Victoria University in Wellington, New Zealand, and lead author of the study.
Although climate change resulting from emissions of carbon dioxide and other greenhouse gases has probably played an important role, the analysis has shown that natural climate variability can account for the entire extreme temperature balance, effectively masking any contribution caused by man.
“The interior of Antarctica may be one of the few remaining places on Earth where the anthropic signal cannot be easily triggered due to this extreme variability,” said Clem.
“But it is very, very unlikely that you have such a strong heating trend without increasing greenhouse gases,” he added.
Temperature records at the pole have been maintained since 1957, when the first American base was completed there. For decades, average temperatures have been stable or declining. The strong westerly winds that surrounded the continent served as a barrier, preventing warmer air from entering the interior.
But that changed towards the end of the 20th century, said Clem, when sea surface temperatures in the western tropical Pacific began to rise, part of a natural oscillation that occurs on a decades-long scale.
The heated ocean heated the air, causing waves of high and low pressure in the atmosphere that reached the Antarctic Peninsula, more than 8,000 kilometers away. Scientists call this type of long distance call teleconnection.
Along with the strongest winds from the west, which are part of another long-term pattern, the swells have led to stronger storms in the Weddell Sea, east of the peninsula. These rotating or cyclonic storms swept the warmest air from the South Atlantic Ocean into the interior of the continent.
Stronger storms in the Weddell Sea have also led to a recent decline in sea ice in the region.
Clem said the warming was not uniform on the Antarctic Plateau, the huge expanse that covers most of the interior, including the pole, with an average altitude of almost three kilometers. But the only other permanent base on the plateau, the Russian Vostok station, about 800 miles from the pole, has also seen a rapid rise in temperature, he said.
The waves of the tropical Pacific also affected the Antarctic Peninsula, which for most of the late 20th century was one of the fastest warming areas in the world. But in the past few decades the rate of warming has declined significantly.
In an e-mail message, two researchers at the University of Colorado, Sharon E. Stammerjohn and Ted A. Scambos, said that while the rest of the world has been heating up steadily for the past five decades, Antarctica has undergone major swings and probably always have. None of the scientists participated in the research, but they wrote a commentary on the study published in the same issue of the journal.
As ocean temperatures in the tropical Pacific shift to cooling, they said, the rate of warming at the South Pole is likely to decrease as well, but not as much as it would have been without man-made climate change.
In an interview, Stammerjohn said that “the warming at the South Pole is significant because it is the most remote place on the planet”.
“But it will never be above freezing,” she said. “We still don’t have to worry too much about losing ice on the pole. But definitely the back is another matter. “
Especially along the coast of West Antarctica, the hot water brought in from the depths by the action of the wind melts the shelves of ice underneath, which leads to rising sea levels.
Stammerjohn said there is growing evidence that the way the planet is reacting to warming is changing the atmosphere and circulation of the ocean on a large scale.
“And that is what is contributing to the warmest waters in depth,” she said. “There will be a lot of variability superimposed on that, but the direction and projection would be more and more warm water and more loss of ice sheet.”
“It is so easy to think that Antarctica is isolated and remote and will not respond to climate change,” said Stammerjohn. Although the impact at the South Pole may not be as significant, the loss of ice along the coast has enormous implications.
“It is the one that is going to drastically change the sea level,” she said.
The warming at the South Pole, she said, is “the definitive canary in the coal mine, which we can no longer ignore”.