PHOTOGRAPH BY NASA VIA ALAMY
Published May 13, 2014
The "unstoppable collapse" of glaciers in West Antarctica announced by scientists this week has one key cause: shifting winds. Stronger winds are pushing warm water under coastal glaciers and melting them. The process is expected to intensify in the coming decades.
Two research papers published Monday found that six major glaciers along the Amundsen Sea in West Antarctica are thinning more rapidly than expected and contributing to sea-level rise. Warm water is coming into contact with the bottom of the glaciers as they hang over the edge of the ocean and/or as they "float" over bedrock that is below sea level. (Read "Rising Seas" in National Geographic magazine.)
"Exactly how the warmer waters got there is still somewhat under discussion," says Richard Alley, a professor of Earth sciences at Penn State University in State College, Pennsylvania, who was not involved in either paper but who has studied glaciers extensively.
Changes in wind patterns around Antarctica are considered the most likely source of the warmer water, says Alley. As to why the winds have shifted down south, "global warming, the ozone hole, and natural variability are all suspects—the most likely answer being that all three played a role."
Eric Rignot, a glaciologist at the University of California, Irvine and NASA's Jet Propulsion Laboratory, agrees.
"The key is the recent change in ocean circulation," says Rignot, who was the lead author of a paper on melting Antarctic glaciers appearing in Geophysical Research Letters, a journal of the American Geophysical Union.
"Warm waters are already [present in the area] and are being pushed to a different location." (See interactive: "If All the Ice Melted.")
Winds and Currents
A current of warmer water called the circumpolar deep current encircles Antarctica. It typically lies around 130 feet (40 meters) below the ocean surface and consists of water that is warmer and saltier than the water above.
The reasons for that stratification are complex, says Rignot, and include the cooling that occurs from evaporation at the surface, the impact of rain, and large-scale weather patterns.
The circumpolar deep current is especially close to the coast of Antarctica along the Amundsen Sea. When the winds are strong, they push the warmer water in the current up toward shore and under the glaciers, says Rignot. That causes them to melt faster.
Since the 1970s, those winds have increased in strength by about 15 percent. "That's not outrageous, but it's significant," says Rignot.
He adds that the winds are expected to keep strengthening in the coming decades, which is likely to drive more glacier melt.
Blowing in the Wind?
Antarctica as a whole has not warmed as fast as some other parts of the planet, says Rignot. This temperature differential is the main reason that Antarctica's winds have sped up.
The greater the temperature difference at the pole, the stronger the winds get and the more they shift southward. The southward shift of the strong westerly winds called the "Roaring Forties," which is expected to lead to drought in Australia, is part of the same process, says Rignot.
The hole in the ozone layer also may be contributing by keeping Antarctica colder, thus increasing the strength of the winds, says Alley. Despite the global ban on CFCs, the hole won't really start closing for several decades.
The next step toward understanding this process better is to couple wind pattern modeling with glacier melt modeling, says Ian Joughin, the lead author of a paper on the melting of Antarctica's Thwaites glacier that was published in Science on Monday.
Joughin says his team had based their projections for the demise of the Thwaites glacier on current melting rates. They came up with such a broad range for the loss of the ice, between 200 and 900 years, because they had to account for unknown variability in winds and climate.
Combining climate and wind modeling is "not a trivial step," he says. "For one thing, getting climate right for a thousand years in the future is difficult."
Rignot says scientists are years away from making accurate wind and glacier projections with short date ranges. But he says current understanding still provides plenty of useful information about what's happening in Antarctica, and how that may affect sea level around the world.
A report published last week stated that the rest of the antarctic ice sheet was expanding at a rate faster then expected.Has someone got their wires crossed?
One of the most important glaciology papers ever written. I think it it the most important.
West Antarctic ice sheet and CO2 greenhouse effect: a threat of disaster (January 26, 1978)
Richard Alley say's that they DO NOT KNOW how the warmer water got there.
How did you arrive at the wind conclusion? Dream it? I know, you created a model that predicted it.
How many models, till you got one that agreed with you?
I would like to propose that the shift in magnetic poles has a correlation to ice caps melting? Any comments?
Let's see. Global temps have increased on average 0.5 degrees C since 1970 and this negligible amount of warming (whatever its cause) is responsible for a shift in the winds which in turn is responsible for the glacial melt? Crock of you know what is being served up here (which is not to say that there has been some global warming which may have been caused at least in part by human activity).
@Doug Hornby They use our hard earned tax money to test their models and explore their theories so they can come up with some sensational results and get more grants. If their models didn't show anything alarming there would be no interest and therefor no more money. It's a big racket. Now instead of focusing our efforts on fighting poverty or fostering peace we have to worry about the ice melting and we pay more for electricity in the form of carbon taxes. All the while these sophomoric so called scientists think they're important. If they had to worry about actually ever getting a real job or contributing something to society the wind at the south pole would be the least of their concerns.
Ocean winds keep Antarctica cold, Australia dry
“The Southern Ocean winds are now stronger than at any other time in the past 1,000 years,” Abram said.
“The strengthening of these winds has been particularly prominent over the past 70 years, and by combining our observations with climate models we can clearly link this to rising greenhouse gas levels.”
@Oliver Kibbel I hadn't come across that idea. What would the mechanism be?
@Doug Hornby @Steve Russin Merely because you have an apparent issue with science in general does not mean that research scientists are fudging sensationalist data to protect their funding streams. There is solid data, if you choose to actually consider it. I think it's disturbing that you think scientists are "sophomoric" and don't have "real jobs." By the power of deductive reasoning we can also then deduce that you think these scientists who are inept in your opinion, should focus their efforts on fighting poverty and fostering peace. Wow! But we still have some general hurdles to overcome, in the form of refusal to accept the global climate change truth that's in the data. Have a great day!
Tree rings, ice cores, and lake proxies. More and higher piled crap. Just like the study that shows storms moving farther south and north. pure unadulterated waste.
Give us hard un-modified data. Not computer generated dreams.
@Brian Howard @Oliver Kibbel Hey Brian - I have another crazy theory (I use that term loosely) - With the sharp and steady increase in humanity's numbers (+- 7 billion?), and with percentage composition of human being +- 70%(?) water - where is all of this water being taken from, seeing that it is now being stored in human vessels?
@Mark Pommier @Doug Hornby
My point is that what you believe and try and coerce others to believe is proof positive of climate change theory I will question. You will try and show me ice samples with CO2 deposits in them and temperature scans from satellites and I will take them into consideration, but until you actually accomplish something in the way of correcting these problems you have done nothing. The argument will always come down to methods and there will always be flaws so you must be more careful when you purport them as absolutes... it dampens your credibility. When you simply scoff at any non-believers you come off as pompous and condescending and that is why people don't appreciate being spoonfed this style of pseudo-science. Climatologists are to science as chiropractors are to medicine, neither ever really accomplish anything significant. (Be happy I didn't call them snake oil salesmen) As far as my opinion of scientists I'll tell you that the real ones are working for chemical companies and natural gas companies, not making a living off of grants from the taxpayers or wallowing in academia. Also, try and sound a little less unhinged next time you reply to my statements. Thanks.
Feed the World
How do we feed nine billion people by 2050, and how do we do so sustainably?
We've made our magazine's best stories about the future of food available in a free iPad app.
Latest From Nat Geo
These cooing Casanovas use showstopping plumage to court females and fend off rivals.
Meet a trapper who keeps Florida's streets, sewers, and Kennedy Space Center alligator free.