VOA慢速英語:為什么南極在變冷？
Many scientists believe climate change exists. They say temperatures on Earth’s surface are rising. And they say human beings are largely responsible for the warmer conditions. But the opposite seems to be happening in Antarctica. Surface temperatures there are falling. A new study that explains these changes.
Like the folksinger Bob Dylan said, "The answer my friend is blowin' in the wind."
Nerilie Abram is the lead author of the study. She works as a climate scientist with the Australian National University. She says the most important influence on weather in Antarctica is the wind.
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The ship MV Akademik Shokalskiy is pictured stranded in ice in Antarctica, December 29, 2013. |
“They control how far north the rain bands go out of the Southern Ocean. 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 out into the path of those westerly winds.”
The westerly winds travel around the continent. The study found that they are now stronger and their path tighter than at any time in the past 1,000 years. That change has been especially noticeable since the 1940s.
The study was published in the journal Nature Climate Change. Ms. Abram and her team attempted to recreate Antarctica’s climate history with ice taken from the continent. They found the wind has kept large parts of the continent cold.
“But we can explain that because as those westerly winds are getting stronger, they are actually tying the cold air over Antarctica, and it stops warm air masses from being able to get over the continent and help to warm Antarctica. 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.”
Greenhouse gases trap energy from the sun in Earth’s atmosphere.
However, the westerly winds are not having the same effect on the Antarctic Peninsula and parts of the Western Antarctic ice sheet.
“So as those winds have strengthened and pulled in tighter around Antarctica,they are actually bringing warmer air over those parts. And we see really quite marked warming, particularly over the Antarctic Peninsula. And this is the part of the southern hemisphere that is warming faster than anywhere else on Earth at the moment.”
Nerilie Abram says the westerly winds have changed direction from their normal path. Usually, those winds would have forced cold air into the southern hemisphere. Instead, the air is trapped over Antarctica, and keeps 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. And so that is why Australia is experiencing these very severe droughts.”
She adds that the Southern Ocean winds have intensified because of the warmer atmosphere. She says the winds could return to a more normal pattern if action is taken to reduce greenhouse gases.
I’m Anna Matteo.
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