David Vaughan: Future of West Antarctic Ice Sheet Unclear

June 1, 2007

Polar ice experts once thought Antarctica’s ice sheets were mostly immune to climate change. But these days, they aren’t so confident.

Satellites have revealed that the ice sheets are thinning and their glacial slide into the sea is speeding up. Ice cores reveal that at times in the geologic past, Antarctica was ice free. To make matters worse, the West Antarctic Ice Sheet (WAIS), a sheet of ice the size of Texas storing enough water to raise global sea level by 5 meters (about 16 feet), is resting on rock that’s below sea level.

“Not just a bit below sea level, it’s 2,000 meters below sea level,” said David Vaughan, a principal investigator with the British Antarctic Survey (BAS). “If there was no ice sheet there, this would be deep ocean, deep ocean like the middle of the Atlantic.”

Some scientists have theorized that this makes the WAIS inherently unstable. If the ice sheet retreats beyond a certain point, a positive feedback mechanism should, they say, lead to runaway retreat that would not stop until most of the ice sheet disappears.

Vaughan spoke of the uncertain future of the WAIS in a Hot Science, Cool Talk outreach lecture sponsored by the University of Texas at Austin’s Environmental Science Institute and Jackson School of Geosciences. His presentation was the culmination of a three day workshop titled West Antarctic Links to Sea-Level Estimation, which brought together approximately 30 polar ice experts from across the U.S. and U.K. at the university from March 26-28, 2007. The scientists worked to forge greater consensus on the potentially devastating impact that the melting of West Antarctic ice could have on future sea-level rise.

Vaughan led the British half of a joint project between the BAS and the University of Texas at Austin in 2004 to reveal what lies below the WAIS.

Vaughan led the British half of a joint project between the BAS and the University of Texas at Austin in 2004 to reveal what lies below the WAIS.

Using airplanes with radar antennas strapped under the wings and logging tens of thousands of air miles in a couple of months, the two teams were able to create detailed topographic maps of the rocks and sediment that form the bed on which miles of ice sits. The researchers even identified lakes of liquid water which remain unfrozen due to the enormous pressures of the ice above.

The data will be used in computer models to try to answer two burning questions for climate scientists: How will the West Antarctic Ice Sheet respond to climate change? And how much will it contribute to sea level rise?

“We have a role to provide the best projections of what is going to happen to this planet over the next few hundred years so people can adapt and also so we can choose how we conduct our lives and the future impact we might have on the planet,” said Vaughan.

Is Antarctica’s Climate Changing?

It turns out that Antarctica is an odd bird when it comes to climate change. According to the Intergovernmental Panel on Climate Change (IPCC), an international group of climate scientists organized by the United Nations and the World Meteorological Organization, climate models now do a good job of replicating (or “hindcasting”) past climate and forecasting future climate trends for every region of Earth except one: Antarctica.

The West Antarctic Ice Sheet, a sheet of ice the size of Texas, stores enough water to raise global sea level by 5 meters (16 feet) if it were to entirely melt. Scientists estimate that it will take centuries of global warming to melt the whole ice sheet.

Several decades of observations there seem to be out of step with computer models.

“Over a large part of the coast of Antarctica, we haven’t seen warming or cooling that we can be sure has statistically happened,” said Vaughan. Coastal temperatures rise and fall considerably from year to year but haven’t followed any clear trend in recent years.

Vaughan said this might be due to circumpolar currents—flows of water and air hugging the continent in a big loop. They tend to isolate it, keeping it colder than it would be otherwise.

There are of course exceptions to the exception. The Antarctic Peninsula, a rocky arm jutting out towards South America, has experienced dramatic warming in recent years, in some spots several times the average warming of the rest of the planet.

Here, the effects of global warming are quite visible, as Vaughan showed the audience.

Penguins are moving to more comfortable locations. More flowering plants are growing on the peninsula. And climate changes might be opening the door to new, invasive plant species. Eighty percent of the peninsula’s glaciers are in retreat. The landscape around one research base that Vaughan has visited periodically for decades is changing rapidly.

Vaughan's research base in 1985, surrounded by ice. “I don’t have a picture of how it looks today because the base is surrounded by water,” said Vaughan. “You no longer come out and hop on a skidoo to ride across the ice to the airstrip. You have to get into a raft and paddle.”

In a slide showing the base in 1985, a red hut sits on the side of a glacier, ice all around.

“I don’t have a picture of how it looks today because the base is surrounded by water,” said Vaughan. “You no longer come out and hop on a skidoo to ride across the ice to the airstrip. You have to get into a raft and paddle.”

Penguins are feeling the changes too.

“If you’re a penguin or something living on the Antarctic peninsula, things have changed substantially,” said Vaughan. “Penguin’s rookeries that have been occupied for 500 years have been recently abandoned and the penguins have moved south with the climate. Other penguins who like warmer conditions have moved in to fill up those rookeries.”

Other parts of the continent are showing signs of change too. Large ice shelves, such as the Larsen B ice shelf, have broken off and floated out to sea.

Antarctic researchers are struggling to understand the contradictory evidence. It’s why the IPCC largely left the possible melting of the West Antarctic Ice Sheet out of its sea level rise predictions.

“The whole planet is not going to rise in temperature at the same rate,” said Vaughan. “Some areas like the Antarctic Peninsula will warm much more rapidly. Others, we’ll struggle to see that they’re affected. Some areas will get wetter and other areas may get drier. We scientists really don’t have the skill to predict where those changes will be. That’s got to come. That’s a major task to achieve over the next ten years because without that regionally specific skill, we don’t have the tools we need to prepare ourselves for climate change.”

“If you’re a penguin living on the Antarctic peninsula, things have changed substantially,” said Vaughan. “Penguin’s rookeries that have been occupied for 500 years have been recently abandoned and the penguins have moved south with the climate."

Sea Level & Antarctica

There’s so much uncertainty about how the climate of Antarctica is changing that when the world’s climate experts got together to hammer out an estimate of future sea level rise for this year’s IPCC reports, they essentially left out contributions from Antarctica.

“Basically, [the IPCC report] says we know most of the things going on to cause sea level rise, we can evaluate them and we can project them into the future,” said Vaughan. “But there are some things we just don’t know enough about and those are the Greenland and Antarctic ice sheets, how they will respond to climate change, how they will continue changing in the future. So that’s one of the reasons we’re down there doing the work.”

Right now, 10 million people are displaced from their homes each year due to coastal flooding. If seas rise 44 centimeters by 2050 (a mid-range estimate of the IPCC), the ranks of the displaced would swell to 100 million people each year.

Vaughan said there is reason to worry that Antarctic melting might boost sea level rise much higher than the IPCC’s estimate. He pointed out that the West Antarctic Ice Sheet (WAIS) is resting on rock that’s 2,000 meters below sea level. Some scientists have theorized that this makes the WAIS inherently unstable.

“We have this really very plausible theory that if you kick this part of the ice sheet hard enough—cause that instability to start feeding back on itself and a retreat to begin—then you could lose that whole area quickly,” said Vaughan. “Now ‘quickly’ probably means centuries, but if you lose all of the West Antarctic Ice Sheet, you’re talking about five meters of rising sea level and you get a scary map like this which shows Cambridge, England, where I live, underwater.”

Map of Great Britain showing projected sea level rise by the year 2050. Areas in red are currently dry land, but are expected to be underwater. Courtesy of British Antarctic Survey.

“Five meters is an enormous amount of sea level rise and would do us untold damage,” said Vaughan. “It’s probably going to take thousands of years, but long before we get to that, coastal areas will start to see more frequent flooding and the big storms that happen every few years will just become that much more frequent.”

For developed countries, sea level rise will be expensive. Flooding caused by Hurricane Katrina devastated New Orleans in 2005. Citizens, governments, insurance companies and aid agencies have spent tens, if not hundreds of billions, of dollars on repairs and reconstruction.

The city of London is considering a costly redesign of the Thames Barrier, an enormous flood gate that closes a few times a year to protect citizens along the Thames River from storm surges. Vaughan said another meter of sea level rise would force officials to close the barrier 300 times a year.

Developing countries are the most vulnerable to sea level rise.

“If you live in the developing world, everything about the developing world makes this worse,” said Vaughan. He cited poverty, substandard housing, inadequate transport systems and ineffective governments as barriers to preparing for and recovering from coastal flooding.

“Imagine if you had to evacuate New Orleans not with cars and helicopters, but with rickshaws,” he said.

Science & Policy

As a scientist, Vaughan sometimes feels like a passenger riding in a car. In this analogy, the driver is a policy maker and the car is our planet. (He shows a photo of his own wife driving their car, but looking at the camera. Vaughan is in the passenger seat, looking warily at the road.)

“Scientists are sitting there, we can see dangerous things in the road ahead,” Vaughan said. “If [the policy maker] turns the wheel early, we may be able to avoid most of that dangerous stuff.”

“Scientists are sitting there, we can see dangerous things in the road ahead,” he said. “If she turns the wheel early, we may be able to avoid most of that dangerous stuff. If she leaves the wheel locked, if she puts her foot on the gas and accelerates, then that thing that’s going to happen is going to be worse.”

While he said it would be nice to just grab the wheel, he acknowledged that would not be practical.

“We can urge caution,” he said. “We can say, ‘slow down.’ This is our role— to advise, to predict. We can say, ‘If we don’t slow down soon, we’re going to get such and such an impact. If we can turn the wheel a little, we may get less of an impact.’”

The real problem is that scientists aren’t certain what will happen.

“To some extent, we don’t know because we don’t know what’s in the road,” said Vaughan. “We don’t know how well the car will break. We certainly don’t know what policy decisions are going to be made to change the course of what’s going on. We can see for the climate debate some danger in the road, we can see some potential for sea level rise in the future. We can’t give you rock solid predictions but we can say what we think the uncertainties are and try to reduce them.”

by Marc Airhart

For more information about the Jackson School contact J.B. Bird at jbird@jsg.utexas.edu, 512-232-9623.