全球气候变暖 南极保持低温

Intense winds help Antarctica keep its cool despite climate change, according to a new study.

Scientists overwhelmingly agree global warming exists and humans are largely responsible, but Antarctica seems to have bucked the trend, with portions of it cooling, while the rest of the planet heats up.

The key to Antarctic weather is the wind, says Australian National University climate scientist Nerilie Abram, lead author of a new study that explains this in the context of a warmer world.

“They control how far north the rain bands go out of the Southern ocean," Abram said. "And they are also really important for temperature and in particular for the temperature of Antarctica and also the Antarctic peninsula, which is the bit of Antarctica that juts out right into the path of those westerly winds.”

That westerly wind belt circulates the continent. The study in Nature Climate Change finds that those winds are now stronger and their path tighter than at any time in the past 1,000 years. That change has been especially prominent since the 1940s.

Abram and her team reconstructed Antarctica's climate history from ice cores. They conclude the wind has kept a large part of the continent cold, unlike anywhere else on the planet.

“But we can explain that because as those westerly winds are getting stronger, they are actually tying [trapping] the cold air over Antarctica, and it stops warm air masses from being able to get over the continent and help to warm Antarctica," Abram said. "So this example of something that seems like a climate change paradox, we can actually explain by these greenhouse gases that are strengthening the westerly winds and isolating parts of Antarctica.”

But they are not isolating the Antarctic Peninsula and parts of the Western Antarctic ice sheet that lie directly in their path.

“So as those winds have strengthened and pulled in tighter around Antarctica, they are actually bringing warmer air over those parts, particularly over the Antarctic Peninsula," she said. "And this is the part of the southern hemisphere that is warming faster than anywhere else on Earth at the moment."

Those westerly winds have deviated from their natural course, which would have driven cold fronts into the southern hemisphere. Instead the air is trapped over Antarctica and keeping rain from falling on Australia.

“What has been happening over the recent decades is that those westerly winds have been shifting south and we are getting fewer of those cold fronts and storms coming up and giving that really important rain," she said. "And that is why Australia is experiencing these very severe droughts.”

Abram adds the Southern ocean winds, which have intensified because of the warmer atmosphere, could revert to a more normal pattern if action were taken to reduce greenhouse gases.