Antarctica was seemingly the only continent on Earth that had not been warming up, as far as scientists could tell. But now a new study finds that large parts of the southern continent have in fact been getting warmer.
Researchers are particularly interested in Antarctica's fate because the coastlines of the world would be obliterated if Antarctic ice melted away and raised global sea level.
The continent is so remote, scientists didn't put permanent weather stations there until 1957 — and even those were in just a few scattered places. Eric Steig at the University of Washington says that made it hard to take the continent's temperature.
"It's like having data in San Francisco and New York and trying to say something about Arizona," says Steig. "You really need some more information if you're going to say anything reasonable about Arizona."
Steig and his colleagues have done just that for Antarctica, taking the sparse temperature records of the past 50 years and combining them with satellite records that cover a much greater area, but don't go back so far in time. Combining those records, they now report that a big chunk of Antarctica — the western part of the continent — has in fact been warming up, like the rest of the world.
Temperatures have risen by about 1 degree near the equator to more than 5 degrees near the North Pole.
"It's much less than Arctic warming but it pretty much is on par with global average warming," Steig says.
Forecast: More Snow
Up to a point, Antarctic warming can actually reduce sea level. Warming there can take water out of the ocean and deposit it on the continent, in the form of increased snowfall.
"West Antarctica should be getting more precipitation along with this increased temperature. But I think the data to demonstrate that are not really available," Steig says.
In fact, the best data from Antarctica show that the continent is putting slightly more water into the ocean than it's taking out.
Previous studies have not found a warming trend in Antarctica. Steig's conclusion is therefore a shift, but it's not a total surprise.
"This one study should not cause anyone to suddenly get more worried. If they are taking it seriously already, then this should not make them change their view particularly," he says.
In fact, Arctic scientist Richard Alley at Penn State University says he finds the new information reassuring — in a way.
"The world looks a little more sensible to me than it did before," he says.
That's because many scientists expected that Antarctica should be warming up, along with the rest of the world. It was a bit of a mystery why it didn't seem to be doing so. And the consequence of warming Antarctic air is not cause for panic, Alley says.
"For now, most of the Antarctic is still so cold that it's very hard to melt it from above. The big question for Antarctic for the near future is what happens to the ocean," he says, "because the warm ocean waters can circulate under the floating extensions of Antarctica — the ice shelves."
And if warmer water melts those ice shelves, they'll release mountains of ice behind them into the ocean.
Scientists have already seen some dramatic changes to ice shelves on the Antarctic Peninsula, which juts toward South America and is warmer than the rest of the continent. The relatively small peninsula has been a major exception to the rule for Antarctica; it clearly has been heating up in recent decades. At least eight large ice shelves around the peninsula have melted away.
David Vaughan from the British Antarctic Survey is on the peninsula right now, keeping a worried eye on the Wilkins Ice Sheet. It was once larger than Connecticut but soon could be gone entirely.
"We landed on the ice shelf just two days ago — flimsy looking piece of ice — and that appears to be hanging on by the skin of its teeth," Vaughan says.
It could collapse any time in the next few weeks, he says.
"Not all of Wilkins will disappear overnight but a large part of it could," Vaughan says.
This ice sheet is already floating on the ocean, so when it melts it won't raise sea level. But it's a powerful reminder that change can come quickly — and dramatically — in this land of ice.