Science, Tech & Environment

Sea Levels May Rise Faster Than Expected

Penguin-Michael-Van-Woert-NOAA-NESDIS-ORA.jpg

Credit: Michael Van Woert, NOAA NESDIS, ORA
Emperor Penguins adults with chicks in Antarctica.
Unpublished

As climate negotiators slog through the latest UN summit in South Africa with no breakthrough on greenhouse gas limits in sight, the science of climate change–especially melting ice–is racing ahead of the world's response to the problem.

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The day after this year's UN climate summit ends this Friday, a research team is scheduled to fly into a remote corner of Antarctica for a visit to the Pine Island Glacier. It's the biggest ice shelf in western Antarctica. And it's moving–fast.

"This is the fastest glacier in Antarctica," says Robert Bindschadler of NASA, the expedition's leader. "It's going 4,000 meters a year, which converts to just over one foot every hour. So this ice is ripping along."

Bindschadler says the reason the ice is moving so fast is because unusually warm ocean water is seeping in miles under the glacier's forward edge, melting it from below.

"In the case of Pine Island, we think that it's melting at over a 100 meters per year right at the upstream end of the ice shelf. And you think the ice shelf by that amount, the glacier speeds up by many tens of a percent."

Scientists compare what's happening to the glacier to popping the cork on a champagne bottle. But in this case, what's being held back is frozen water.

And it's not just one glacier. There are signs of sudden, rapid melting across Antarctica, where all the corks on all the glaciers and ice sheets are holding back enough water to raise global sea levels more than 200 feet. The faster that ice melts, the faster the world's coastlines will be inundated.

The problem is, no one saw this coming.

"It's caught us all very much off guard," says Bindschadler. "These are not the ice sheets that I was being taught when I was in graduate school. They are changing at magnitudes and at rates that were thought impossible just 15 years ago."

That rapid melting is challenging assumptions on how much global warming will cause sea levels to rise this century.

The last major report from the Intergovernmental Panel on Climate Change, or IPCC, in 2007, suggested a worst-case scenario of less than two feet of rise by 2100. But Virginia Burkett with the US Geological Survey, a lead author on the report, says there was a big caveat.

"The last IPCC report included sea level projections that were based primarily on thermal expansion," of the water as it warms up, Burkett says. "And of course sea level is rising because of the combination of thermal expansion of sea water and ice sheet decline."

The problem was that the science on ice sheet decline, or melting polar ice, just wasn't good enough at the time, so the IPCC decided to leave it out of their final projections. And even though the report's fine print clearly stated that ice loss could accelerate substantially, that number of less than two feet has become a kind of default prediction for sea level rise.

Fast forward five years and scientists like Bindschadler and Burkett are now projecting a high-end scenario of about six feet of rising sea levels by the end of the century. Three times the 2007 projection.

That's enough to make crowded coastal cities like Mumbai unlivable, and displace more than a 100 million people worldwide. But some scientists say even a prediction of six feet may be too conservative.

Harold Wanless, chair of the Geology Department at the University of Miami, says all the projections by the IPCC and other scientific organizations are based on a gradual rise of sea level. But, Wanless says, "that's not how it worked in the past."

Scientists like Wanless are studying sediments from past warming periods to find clues as to how quickly sea levels changed. And what they've found is the stuff of Hollywood movies–rapid pulses in the 20-foot range, and on a time scale that could be not centuries, but decades.

"That's in the line of possibility," Wanless says. And he warns that it's time to start thinking about relocating things that countries don't want to lose.

"Everything from national archives and our world seed banks, some of which are at much too low elevation. Military bases, things we wouldn't want disrupted. And our nuclear power plants. Why are we even looking at the coast for those?"

Wanless believes the ice sheets in Antarctica and Greenland have already passed their tipping point for runaway melting. The only question for him is how fast it will happen.

Most climate scientists don't go that far. They say they still don't understand the complex dynamics of ice melt enough to predict with confidence a 20-foot rise by the end of the century. But few are ruling it out.

Penn State Climatologist and IPCC co-author Richard Alley says a good analogy of the risk is driving a car. The best scenario, Alley says, is that there's no traffic. On the other hand, you might get a lot of traffic, or "you might get run over by a drunk driver."

The drunk driver represents that rapid pulse of sea level rise. Alley says even though the chances of him being hit are slim, he still bought a car with all the added safety features, just in case.

"If society dealt with risks of climate change the way I deal with drunk drivers," Alley says, "it's possible that we would be trying to slow down a little bit so that we could learn more before we get hit by something."

What's happening instead is more like stepping on the accelerator. As climate negotiators from the US, China and nearly every other country on earth met this week to again try to find elusive common ground on emissions cuts, new reports confirmed that global emissions of the heat-trapping gas carbon dioxide reached record levels last year.

Alley says the higher we crank up the planet's thermostat, the higher the risk becomes that we'll get hit by something nasty.

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