ALEX CHADWICK, host:
Now to another scientific challenge. The massive ice sheets in Western Antarctica are melting. And according to a new report, they're melting faster than anyone had predicted.
Eric Rignot joins us now. He's the lead author of the report, which appears in the journal Nature Geoscience. He's a professor at the University of California in Irvine.
Professor, welcome. And what is the change in the rate of ice melting in Antarctica? What have you found?
Dr. ERIC RIGNOT (University of California, Irvine): What we found is that the mass loss from the Antarctic ice sheet increased by 75 percent in the last 10 years, almost a doubling of the mass loss.
CHADWICK: And how does this compare to what predictions had been?
Dr. RIGNOT: Well, predictions mostly based on climate models has been that the Antarctic ice sheet is not going to melt until we have much more warming of air temperatures. We're finding, in fact, the opposite of what the climate models have predicted. We're finding that the ice sheet is losing mass along the edges of the continent. And the Antarctic ice sheet is not really warming, but we believe that the changes that we're observing are related to changes taking place in the ocean.
CHADWICK: Well, that's my next question. Why is this taking place? What is happening?
Prof. RIGNOT: Obviously, there's no warming that could melt the ice from the top and we know that all these glaciers are entering contact with the ocean, and if the ocean gets warmer, it would explain the trend that we're observing right now on these glaciers.
CHADWICK: But this is not actually the water that's at the surface of the ocean? It's water underneath the ocean?
Prof. RIGNOT: It's water that sits typically a few hundred meters below the surface, which is called the second polar current, which goes around the periphery of Antarctica. And in some cases this current can fluctuate and somehow can upwell and leak onto the continental ice shelf and reach the glacier grounding lines.
When it does that, it increases the melt rate of the glaciers from underneath. The glaciers feel less resistance to flow and they can accelerate. There's already documented evidence of the presence of these warm waters on the continental shelf. What we don't know, however, is how long this has been going on, because there's not enough historical data on ocean temperatures along the Coast of Antarctica to say when this started in the past.
CHADWICK: Professor Rignot, for a listener who gets a lot of kind of climate change news, how do you evaluate this report with all the other data?
Prof. RIGNOT: Well, it shows that the changes in the climate system is complex. It's just not a warming of air temperatures. It has a lot of ramification. The pace of change of these ice sheets have been largely underestimated by models; things are changing on a much faster pace than what these models predicted.
CHADWICK: The ice in Antarctica, Professor, it's especially important because that's 90 percent of the world's ice.
Prof. RIGNOT: That's right. If you melt all the ice in the Antarctic, into the ocean, it would raise sea level by some 70 yards.
CHADWICK: Seventy yards?
Prof. RIGNOT: Yeah.
CHADWICK: The predictions I have read say that we should expect no more than, at a maximum, two feet rise in surface of water from melting ice over the next 100 years, and probably less than half of that. Do you think those predictions are wrong now? Is the situation more alarming than we thought?
Prof. RIGNOT: Well, I don't think the predictions are wrong. You just have to note that they don't include contributions from Greenland and Antarctica as a result of rapid change in glacier flow. So the numbers that are put out there do not include potential contribution from ice sheets. The scientific committee has been quite conservative in putting these out.
CHADWICK: Professor Eric Rignot of the University of California at Irvine. He's lead author of a report on melting ice in Antarctica in the journal Nature Geoscience.
Professor, thank you.
Prof. RIGNOT: Thank you.