01/18/2019

Antarctic Ice Is Melting—And It’s Melting Faster

11:38 minutes

an arial shot of a large chunk of a glacier missing
Thwaites Glacier in Antarctica. Credit: NASA

Researchers monitoring the condition of the Antarctic ice sheet report that not only is the ice melting, but that the rate of ice loss is increasing rapidly. According to their estimates, around 40 gigatons of ice were lost per year in the 1980s. By the 2010s, that rate of loss had increased to more than 250 gigatons of ice per year. That melting ice has caused sea levels around the world to rise by more than half an inch, the researchers say.

Eric Rignot, climate scientist at the University of California-Irvine and one of the authors of the report, joins Ira to discuss the trends in the ice sheet and what they portend for sea level rise. 


Further Reading

Read the report on Antarctic ice loss. [PNAS]

Segment Guests

Eric Rignot

Eric Rignot is Chair and Donald Bren Professor of Earth System Science at the University of California, Irvine in Irvine, California.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. 

Researchers monitoring the condition of the Antarctic ice sheet report that not only is the ice melting– no surprise– but that the rate of ice loss is increasing rapidly– and I mean very rapidly. In fact, they found that over the past 40 years, the rate of ice loss has increased by about six-fold. So what are the implications? 

Joining me now is Eric Rignot. He’s a climate scientist, University of California Irvine, and NASA’s Jet Propulsion Laboratory, And one of the authors of a report on the melting ice sheet published this week in the proceedings of the National Academy of Sciences. Welcome to the program. 

ERIC RIGNOT: Thank you. 

IRA FLATOW: That must have been very surprising, how fast that ice is melting. No? Wasn’t surprising? 

ERIC RIGNOT: Yes, it has been. I think the incentive of this study was really to try to reconstruct a long-term record, multiple decades. The exact number of the six-fold increase in Antarctic mass loss was probably not a complete surprise. But we were very happy to be able to reconstruct these four years of data for the Antarctic. 

IRA FLATOW: Give us some perspective on how much is melting. What is the massive amount of water that’s melting? 

ERIC RIGNOT: Yes, so we’re talking about, at present day, about 250 billion tons of ice that are sent in the ocean in excess of what the Antarctic should do to maintain the same mass. So that’s a little drop of water compared to what’s in the Antarctic total volume of ice. But on the human scale, to put things in perspective, 1 billion ton is the consumption of water by a city like Los Angeles over one year. So Antarctica is dumping enough water to feed 250 cities like Los Angeles around the world for their fresh water supply. 

IRA FLATOW: Can you actually detect ocean sea level rise with that much water? 

ERIC RIGNOT: It’s a very small signal globally. It’s less than one millimeter per year. So that’s not the real threat. The real threat is the fact that we see this leakage of ice around the Antarctic in some critical sectors. And we know that with time these sectors will release even more ice and have the potential to raise sea level by several meters. 

IRA FLATOW: So what you’re saying is that the water can release the pent up ice that’s on the continent, and it will flow into the ocean? 

ERIC RIGNOT: Yes, every amount of ice that you displace from resting on land to floating in the ocean displaces sea level, raises sea level worldwide. 

IRA FLATOW: That’s amazing. Is the melting, is it melting evenly around the continent? 

ERIC RIGNOT: Yeah, so the melting is actually a little bit of a dangerous word in the case of the Antarctic because I would assume that our audience would see the ice melting from the top snow and melting, and it’s not the way it works in the Antarctic. The way it works is that the glaciers, the rivers of ice that control how much ice is flowing from the continent to the ocean are flowing faster. So they’re sending more icebergs and melting more vigorously with the ocean than they did in the past. The net effect is to have more ice melting in the ocean. But it’s proceeding in a slightly different way than we are used to when we talk about the glacier melting because of a warm climate. 

And what we knew before this study was that there was a lot of so-called melting in the Antarctic Peninsula, the little part of Antarctica that sticks out towards South America and West Antarctica, a particular sector of West Antarctica. And now we see that East Antarctica, a big sector of that is also a participant in the melt. 

IRA FLATOW: So the parts near the warm water are melting faster. The warming ocean is sort of a heat source. 

ERIC RIGNOT: Exactly. All these parts that are melting rapidly right now are close to the sources of warm ocean water. The places that are far away from these warm water are actually not changing at all. That’s sort of bit in contrast with a place like Greenland, where we see melting everywhere in Greenland, all around the periphery of Greenland. In the Antarctic, it’s not affecting everything, but the places that are close to the warm water are affected and responding. 

IRA FLATOW: Does the cold, the melting of the water, and the change in the ice, does that affect the larger climate system, like the winds that surround the pole? 

ERIC RIGNOT: So the winds are affected by climate change. And they affect ocean circulation in the southern hemisphere in a way that pushes this subsurface salty warm water more towards the coast of the Antarctic. It’s in this matter that it works. The feedback of that excess melt water into the system is a little bit different. It might affect the formation of deep water around the Antarctic, but it’s a little bit of a trickle compared to the general pattern of ocean circulation around the Antarctic. 

IRA FLATOW: How did you measure? How do you measure all that melting of the water? 

ERIC RIGNOT: So it’s mixing a large amount of data. We have to calculate what we call the flux of ice into the ocean, how fast the glaciers are transporting ice into the ocean. So we need to know the speed of that ice and the thickness. The speed is measured by satellites. And we use satellites from five or six different space agencies. The ice thickness is measured from airborne radio echo sounding. And these data have been collected over the past decades by various programs. This way we can constrain how much ice Antarctica is sending into the ocean. 

And then we have to compare that with the accumulation of mass in the interior. And this is done by regional atmospheric climate models. In this case, models from the University of Utrecht in the Netherlands, they employ what we call real analyst data. So it’s an ensemble of meteorological data worldwide that have been put together, massaged and formatted together. 

And they run a high resolution model in the Antarctic to reconstruct exactly the snowfall pattern on the Antarctic. And we use that to calculate how much ice should be coming out of these glaciers and compare that with what’s actually coming out. And the difference is the net mass lost to the ocean. So to do this accurately, we need the most accurate velocity, the most accurate ice thickness. We need to bring these regional atmospheric climate models to a level of precision that’s exceptional. 

IRA FLATOW: Is there any reason to believe that the rate of melting might slow down or stop? Or is it going to get faster as time goes on? 

ERIC RIGNOT: It’s going to get faster for two main reasons. One is just the internal dynamics of ice. When you disturb a glacier, it starts responding slowly. And with time, as you keep pushing it, it responds faster and faster. It has a sort of a non-linear response to climate forcing. The other one is that, based on our understanding of how the climate is acting on the Antarctic right now– I mentioned the winds that are spinning up more rapidly around the Antarctic continent and pushing more of these subsurface water towards the continent– this trend should continue as climate keeps warming around the planet and the temperature difference between the Antarctic and the rest of the world keeps getting higher. 

IRA FLATOW: Is there a tipping point in Antarctica where if glaciers melt in the correct or the right place, you open up, you release a dam that allows a sudden flow of ice into the ocean? 

ERIC RIGNOT: Yes, there is something like a tipping point. In the Antarctic, you could probably argue that different parts of Antarctica have different tipping points. And we’re not exactly sure what these tipping points might be. 

In the West Antarctic, we made an announcement four years ago that we thought we passed the tipping point for the Amundsen Sea abatement part of West Antarctica, because the glaciers nowadays are retreating into a deeper ground with very little bumps and ridges upstream that could slow down their retreat. And we know from basic physics that when glaciers start retreating in the landscape where the bed elevation drops as you go inland, it’s unstable. And the only stable state of these glaciers is to become completely afloat in the ocean. 

So we think that we reached that tipping point already in West Antarctica. How fast the glaciers retreat will depend on climate forcing, will depend also on the course of humanity in controlling climate forcing. In the East Antarctic, I don’t think we’ve reached that tipping point yet on some of the key glaciers, but we’re probably not too far from it either. 

IRA FLATOW: How far is that? Not too, too far? 

ERIC RIGNOT: Well, to answer that question, we usually need to get to another level of details in our study. So in the case of the West Antarctic ice sheet, for instance, I think we had a good idea that something important was taking place there back in the late 1990s. In 1997 and ’98, we thought something big was happening there. And we waited until 2014 to make a little bit of noise about the fact that we thought that the plug had been pulled in this sector. 

Because in between, we conducted very extensive surveys, surveys conducted not just by NASA, but by the National Science Foundation, by foreign entities like the British Antarctic surveys, and others. We had to collect a lot of data, especially to characterize what the bed topography looked like underneath the ice to sort of figure out, what kind of configuration do we have here? Is it conducive to a fast retreat or not? We have to make sure we map every little bump in the system before we say something. 

So in East Antarctic, we’re not there yet. We need a little bit more work to figure out that level of detail. And a ridge and a bump here and there makes a difference. 

IRA FLATOW: All right, Dr. Rignot, we’ll have you back when you get better figures on that. So thank you for taking time to be with us today. 

ERIC RIGNOT: You’re welcome. 

IRA FLATOW: Eric Rignot is chair, and Donald Bren professor of Earth System Science at the University of California at Irvine. 

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