Antarctica Is Warming, Not Cooling: Study

Alister Doyle, PlanetArk 22 Jan 09;

ROTHERA BASE - Antarctica is getting warmer rather than cooling as widely believed, according to a study that fits the icy continent into a trend of global warming.

A review by U.S. scientists of satellite and weather records for Antarctica, which contains 90 percent of the world's ice and would raise world sea levels if it thaws, showed that freezing temperatures had risen by about 0.5 Celsius (0.8 Fahrenheit) since the 1950s.

"The thing you hear all the time is that Antarctica is cooling and that's not the case," said Eric Steig of the University of Washington in Seattle, lead author of the study in Thursday's edition of the journal Nature.
The west of Antarctica is warming faster than the east, according to the new analysis, as this representation shows.

The average temperature rise was "very comparable to the global average," he told a telephone news briefing.

Skeptics about man-made global warming have in the past used reports of a cooling of Antarctica as evidence to back their view that warming is a myth.

Cooling at places such as the South Pole and an expansion of winter sea ice around Antarctica had masked the overall warming over a continent bigger than the United States where average year-round temperatures are about -50 Celsius (-58.00F).

The scientists wrote that the Antarctic warming was "difficult to explain" without linking it to manmade emissions of greenhouse gases, mainly from burning fossil fuels.

Until now, scientists have generally reckoned that warming has been restricted to the Antarctic Peninsula beneath South America, where Britain's Rothera research station is sited.

Temperatures at Rothera on Wednesday were 2.6 C (36.68F).

WEST ANTARCTICA

"The area of warming is much larger than the region of the Antarctic Peninsula," they wrote, adding that it extended across the whole of West Antarctica to the south.

Rising temperatures in the west were partly offset by an autumn cooling in East Antarctica. "The continent-wide near surface average is positive," the study said.

Antarctica's ice contains enough frozen water to raise world sea levels by 57 meters (187 ft), so even a tiny amount of melting could threaten Pacific island states or coastal cities from Beijing to London.

West Antarctica "will eventually melt if warming like this continues," said Drew Shindell, of the NASA Goddard Institute for Space Studies, who was one of the authors. A 3 Celsius (5.4 F) rise could trigger a wide melt of West Antarctica, he said.

Greenland is also vulnerable. Together, Greenland and West Antarctica hold enough ice to raise sea levels by 14 meters.

"Even losing a fraction of both would cause a few meters this century, with disastrous consequences," said Barry Brook, director of climate change research at the University of Adelaide in Australia.

Ten ice sheets on the Antarctic Peninsula have receded or collapsed since the 1990s. The Wilkins sheet is poised to break up, held in place by a sliver of ice 500 meters (1,640 ft) wide compared to 100 km in the 1950s.

Other scientists said that the study did not fully account for shifts such as a thinning of ice sheets in West Antarctica.

"This warming is not enough to explain these changes," said David Vaughan, a glaciologist for the British Antarctic Survey at Rothera, by an iceberg-strewn bay. He said the thinning was probably linked to shifts in the oceans.

The Nature study compared temperatures measured by satellites in the past 25 years with 50-year records from 42 Antarctic weather stations, mostly on the coast. Scientists then deduced temperatures back 50 years.

(Editing by Richard Balmforth)

Antarctica Is Warming: Climate Picture Clears Up
Andrea Thompson, livescience.com 21 Jan 09;

The frozen desert interior of Antarctica was thought to be the lone holdout resisting the man-made warming affecting the rest of the globe, with some areas even showing signs of cooling.

Some global warming contrarians liked to point to inner Antarctica as a counter-example. But climate researchers have now turned this notion on its head, with the first study to show that the entire continent is warming, and has been for the past 50 years.

"Antarctica is warming, and it's warming at the same rate as the rest of the planet," said study co-author Michael Mann of Penn State University.

This finding, detailed in the Jan. 21 issue of the journal Nature, has implications for estimating ice melt and sea level rise from the continent, which is almost entirely covered by ice that averages about a mile (1.6 kilometers) thick. The revelation also undermines the common use of Antarctica as an argument against global warming by contrarians, Mann said.

Ozone and cooling

Not all of Antarctica was thought to be immune to rising global temperatures, of course. Scientists have been watching as the Antarctic Peninsula, the only part of the continent that juts outside the Antarctic Circle, has warmed faster than the global average, and entire ice shelves have collapsed into the south polar ocean.

In stark contrast, a large part of the continent - the East Antarctic Ice Sheet - was found to be getting colder. The cooling was linked to another anthropogenic (human-caused) effect: ozone depletion.

Ozone in the Earth's stratosphere absorbs the sun's incoming ultraviolet rays, protecting living things on the surface (including humans) from detrimental effects. Certain types of manmade chemicals have depleted much of this protective layer over the last few decades.

As ozone was depleted, less radiation was absorbed at this layer of the atmosphere, which altered the layering of temperatures over Antarctica, over which the largest ozone "hole" is found (it's not really a hole, but rather a region of extreme thinning). This in turn altered wind patterns and strengthened the circumpolar vortex, creating a wall of winds that isolated the cold air over Antarctica from the warm air over the South Pacific Ocean, Mann explained.

Essentially, the effect of ozone depletion was "overwhelming the influence of greenhouse warming," Mann told LiveScience. He and his colleagues were able to show this in their study by compiling a more comprehensive temperature profile of Antarctica than scientists have ever had.

Weather stations and satellites

Weather stations have been in place in Antarctica since 1957, but almost all of them are near the coast, providing no information about conditions in the continent's interior.

Satellites are available now that calculate the surface temperature of the interior based on how much infrared light is radiated by the snowpack, but these records only go back 25 years.

The key to the study was comparing the two records and finding that they matched up closely for overlapping time periods. The researchers then developed a statistical technique that used the data from both sources to make a new estimate of Antarctic temperature trends.

"People were calculating with their heads instead of actually doing the math," said lead author of the study Eric Steig, of the University of Washington in Seattle. "What we did is interpolate carefully instead of just using the back of an envelope."

Their work showed that not only was the Antarctic Peninsula warming, but the interior of West Antarctica - the ice sheet most susceptible to potential future collapse - was as well. And not only that, but that "the continent on the whole is warming," Mann said. "This is the first study to demonstrate that."

The study, funded by the National Science Foundation, found that warming in West Antarctica exceeded about 0.18 degree Fahrenheit (0.1 degree Celsius) per decade for the last 50 years - more than enough to offset the cooling in East Antarctica.

And with ozone depletion having leveled off, that cooling is unlikely to continue in the future.

"Efforts to repair the ozone layer eventually will begin taking effect and the hole could be eliminated by the middle of this century. If that happens, all of Antarctica could begin warming on a par with the rest of the world," Steig said.

"The greenhouse signal is now out-competing the ozone depletion signal," Mann said.

The study is "good work," said Kevin Trenberth of the National Center for Atmospheric Research (NCAR) in Boulder, Colo., but he says there are unique aspects of Antarctica's climate that haven't been taken into account. Trenberth was not involved in the Nature study.

One problem is that temperature inversions can bring warmer air down influencing surface temperatures. "This aspect has not been addressed to date," Trenberth told LiveScience.

The authors dispute this comment: "There is no evidence to support Trenberth's speculation, and there is much evidence that he is wrong," Steig told LiveScience.

Steig explained that they saw the same results whether they used satellite temperatures or those from the weather stations that sit a few meters above the surface, which wouldnt' be the case if inversions were an important factor.

Andrew Monaghan, also of NCAR, said that he agreed with the broad findings of the study, which line up with similar studies he has done of Antarctic temperature trends. He told LiveScience that the biggest finding of the study was the warming of West Antarctica, which is part of the broad ice sheet contributing to ice melt - "it's a Greenland-sized chunk of Antarctica," he said.

Monaghan, who was also not part of the Nature study, said that it is harder to generalize to the continent as a whole and that Antarctica has a highly variable natural climate and that "we still don't understand the natural component well at all."

Implications and contrarians

The implications of the findings for the stability of the Antarctic's ice sheets aren't entirely clear yet and will have to be evaluated by ice sheet modelers, Mann said.

The worry isn't so much from East Antarctica, which sits at a higher elevation than the rest of the continent and is so cold (many degrees below freezing) that the few tenths of a degree of warming isn't yet an issue.

But the study likely means that "a larger part of West Antarctica is melting" than previously thought, Mann said.

West Antarctica is more subject to warm, moist storms and because its ice is all landlocked, it could contribute to sea level rise if it melts. (Ice that's floating on the sea does not raise the sea level if it melts.)

Modelers won't be the only ones interested in the study's findings, as other scientists will likely seek ways to independently and directly confirm or refute the data. Mann mentioned one such study that has been submitted to a journal that used holes in the ice to see how temperatures have changed in the past and has confirmed the underlying warming in East Antarctica.

Outside of these impacts, the study also take away "one of the standard talking points of [global warming] contrarians," Mann said. The argument used by skeptics was "how can the globe be warming if a whole continent is cooling," Mann explained.

Mann said that this argument was "disingenuous" to begin with because the cooling caused by ozone depletion was reproduced by climate models, but the new study soundly routs contrarian claims, he said.

Mann is one of the scientists behind the blog RealClimate.org, which aims to explain the science behind climate change. Steig is contributing a post there on the new study to explain the findings.

Study: Antarctica joins rest of globe in warming
Seth Borenstein, Associated Press Yahoo News 21 Jan 09;

WASHINGTON – Antarctica, the only place that had oddly seemed immune from climate change, is warming after all, according to a new study. For years, Antarctica was an enigma to scientists who track the effects of global warming. Temperatures on much of the continent at the bottom of the world were staying the same or slightly cooling, previous research indicated.

The new study went back further than earlier work and filled in a massive gap in data with satellite information to find that Antarctica too is getting warmer, like the Earth's other six continents.

The findings were published in Thursday's issue of the journal Nature.

"Contrarians have sometime grabbed on to this idea that the entire continent of Antarctica is cooling, so how could we be talking about global warming," said study co-author Michael Mann, director of the Earth System Science Center at Penn State University. "Now we can say: no, it's not true ... It is not bucking the trend."

The study does not point to man-made climate change as the cause of the Antarctic warming — doing so is a highly intricate scientific process — but a different and smaller study out late last year did make that connection.

"We can't pin it down, but it certainly is consistent with the influence of greenhouse gases," said NASA scientist Drew Shindell, another study co-author. Some of the effects also could be natural variability, he said.

The study showed that Antarctica — about one-and-a-half times bigger than the United States — remains a complicated weather picture, especially with only a handful of monitoring stations in its vast interior.

The researchers used satellite data and mathematical formulas to fill in missing information. That made outside scientists queasy about making large conclusions with such sparse information.

"This looks like a pretty good analysis, but I have to say I remain somewhat skeptical," Kevin Trenberth, climate analysis chief at the National Center for Atmospheric Research, said in an e-mail. "It is hard to make data where none exist."

Shindell said it was more comprehensive than past studies and jibed with computer models.

The research found that since 1957, the annual temperature for the entire continent of Antarctica has warmed by about 1 degree Fahrenheit, but still is 50 degrees below zero. West Antarctica, which is about 20 degrees warmer than the east, has warmed nearly twice as fast, said study lead author Eric Steig of the University of Washington.

East Antarctica, which scientists had long thought to be cooling, is warming slightly when yearly averages are looked at over the past 50 years, said Steig.

However, autumn temperatures in east Antarctica are cooling over the long term. And east Antarctica from the late 1970s through the 1990s, cooled slightly, Steig said.

Some researchers skeptical about the magnitude of global warming overall said that the new study didn't match their measurements from satellites and that there appears to be no warming in Antarctica since 1980.

"It overstates what they have obtained from their analysis," said Roger Pielke Sr., a senior research scientist at the University of Colorado.

Steig said a different and independent study using ice cores drilled in west Antarctica found the same thing as his paper. And recent satellite data also confirms what this paper has found, Steig added.

The study has major ramifications for sea level rise, said Andrew Weaver at the University of Victoria in Canada. Most major sea level rise projections for the future counted on a cooling — not warming — Antarctica. This will make sea level rise much worse, Weaver said.

New evidence on Antarctic warming
Richard Black, BBC News 21 Jan 09;

The continent of Antarctica is warming up in step with the rest of the world, according to a new analysis.

Scientists say data from satellites and weather stations indicate a warming of about 0.6C over the last 50 years.

Writing in the journal Nature, they say the trend is "difficult to explain" without the effect of rising greenhouse gas levels in the atmosphere.

Meanwhile, scientists in Antarctica say a major ice shelf is about to break away from the continent.

The Wilkins Ice Shelf is said to be "hanging by a thread" from the Antarctic Peninsula, the strip of land pointing from the white continent towards the southern tip of South America.

In isolation

Most of Antarctica's scientific stations are located along the peninsula, and scientists have known for many years that this portion of the continent is getting warmer.

But trends across the bulk of the continent have been much harder to discern, mainly because data from land stations is scarce.

It is somewhat insulated from the rest of the world's weather systems by winds and ocean currents that circulate around the perimeter.

In the new analysis, a team of US scientists combined data from land stations with satellite readings

"We have at least 25 years of data from satellites, and satellites have the huge advantage that they can see the whole continent," said Eric Steig from the University of Washington in Seattle.

"But the [land] stations have the advantage that they go back much further in time.

"So we combined the two; and what we found, in a nutshell, is that there is warming across the whole continent, it's stronger in winter and spring but it is there in all seasons."

They conclude that the eastern region of the continent, which is larger and colder than the western portion, is warming at 0.1C per decade, and the west at 0.17C per decade - faster than the global average.

The 2007 assessment of the global climate by the Intergovernmental Panel on Climate Change (IPCC) concluded: "It is likely that there has been significant anthropogenic (human-induced) warming over the past 50 years averaged over each continent except Antarctica", with the word "likely" in this context meaning "at least 66% probability".

The scientists said this study did not change that picture, with natural climatic cycles probably involved as well as elevated greenhouse gas concentrations.

"It's hard to think of any situation where increased greenhouse gases would not lead to warming in Antarctica," said Drew Shindell from Nasa's Goddard Institute for Space Studies (Giss) in New York.

"We're almost certain that greenhouse gas increases are contributing to this warming, but what's difficult is to attribute this warming and so say how much is down to natural warming and how much down to anthropogenic causes."

Last year, scientists from the UK Met Office used climate models to attribute trends at the poles, and concluded that human emissions of greenhouse gases were largely responsible for the observed warming.

Gareth Marshall from the British Antarctic Survey (BAS), who was not involved in the analysis, commented: "This study shows that, similar to the other six continents, Antarctica has undergone a significant warming over the past 50 years.

"The magnitude of this warming is similar to the rest of the southern hemisphere, where we believe it is likely that human activity has played some role in the temperature increase, and therefore it is also likely that this is the case regarding an Antarctic warming."

Cool analysis

Over the last 30 years, satellites have also shown that sea ice is slowly growing in extent around Antarctica, which some observers say indicates a cooling across the continent or at least in the surrounding seas.

But Walt Meier from the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado, which follows ice trends at the poles, said wind patterns were probably the main reason.

"Around Antarctica, the winds play a much bigger role than they do in the Arctic," he said.

"If they're blowing northwards you can grow ice quite quickly and in contrast if they blow southwards the ice can contract quickly, whereas in the Arctic it's much more constrained (by land masses).

"So this positive trend in the Antarctic is certainly not an indication of any cooling trend."

One region that has seen spectacular losses of ice in recent years is the peninsula.

A BAS team currently on site is reporting that the Wilkins shelf, about 15,000 sq km in area, is probably about to break free.

"It really could go at any minute, and I wouldn't be at all surprised if the final cracks started to appear very soon," said BAS's David Vaughan.

If it does, it will follow the course of other shelves that have made breakaways in recent years, such as the Larsen B in 2002.

Although spectacular, such events are not necessarily due to man-made climate change.

A much bigger question is whether the new analysis of Antarctic warming heralds any major melting in the West Antarctic ice sheet, which could lead to big changes in sea level and global impacts.

"The vulnerability is higher than we thought, but still we face uncertainties in understanding these processes that make it very difficult to forecast when these changes would occur," said Drew Shindell.