IRA FLATOW: This is Science Friday. I’m Ira Flatow. Yesterday, President Obama and China’s president, Xi Jinping, announced that both countries, the world’s biggest polluters, will sign the Paris agreement on climate change. And they’ll sign that on Earth Day, April 22.

Good timing. Because a study out this week suggests a melting Antarctica could pump up global sea levels a lot more than we thought, contributing to an overall rise of five to six feet by the end of the century. Think your grandchildren. And if they’re right, that nearly doubles the more conservative estimates of sea level rise put out by the IPCC.

My next guest is an ice analyst by trade who spent three seasons in both Antarctica and Alaska, and eight in Greenland, and he’s here to weigh in on that all important phase transition from ice to water. Richard Alley, professor of geosciences at Penn State University. And, by the way, he was not involved in this week’s study, but he has collaborated with the authors in the past. He joins us from WQED in Pittsburgh. Welcome to Science Friday.

RICHARD ALLEY: Thank you Ira. It’s my pleasure.

IRA FLATOW: It’s nice to have you. What’s new? What does this new study add to the discussion on sea level rise that we didn’t know before?

RICHARD ALLEY: Right. So we’ve known for a long time that, if you make it too warm, ice melts. And we’ve been warming and ice has been melting, but so far it’s been slow. The rate at which the big ice sheets of Greenland and Antarctica have been shrinking, it would’ve taken them 100,000 years to go away. That’s the equivalent of me going on a diet for a year and losing a third of a potato chip.

Our worry is– I could use a faster diet. Our worry is that we don’t want them on a faster diet, but they could. They could lose weight a lot faster. And this new study has put some new physics into the model that we know could happen and ask what those real physical processes might mean for the future. And it’s not optimistic.

IRA FLATOW: Can you give us an idea what the changes, what the model difference is?

RICHARD ALLEY: Right. So what we’ve seen is that when it– the ice is a big pile that spreads under its own weight, it flows down to the coast, and it makes these floating extensions called ice shelves. The ice shelves are in fiords and they scrape past the side and that friction holds the shelf back, which holds the pile back, and it keeps sea level low and the ice high.

When we make it warm, we break off those ice shelves and that leaves a big cliff of the kind that you might see in front of a beautiful caving glacier in Alaska. And if that cliff is too high, it breaks and it may break rapidly.

Right now the biggest of those cliffs are sort of 30 stories above sea level and almost 10 times that below sea level, but there’s a piece or West Antarctica they could make a much bigger cliff. And bigger cliffs are prone to breaking more rapidly. And when they put in bigger cliffs break faster into the model, a sufficiently large warming makes a big fast sea level rise.

IRA FLATOW: Wow. So it’s actually the rate that it’s occurring. that we’re talking about.

RICHARD ALLEY: It’s indeed the rate.

IRA FLATOW: It’s going to happen faster than we thought.

RICHARD ALLEY: That’s the concern. If we keep warming it. Now, in this new study, if we slow the warming, the ice sheet might not lose its ice shelf and it might stabilize at a place that it has a small enough cliff that all heck doesn’t break loose. But in a really rapidly warming future by late in the century, you get rid of the ice shelf, you get the high cliff, and you get really fast to sea level rise.

IRA FLATOW: What’s amazing to think about this, this is something that is in the lifetime of our families, right? This could be your grandchildren on the coastline someplace. What, the figure was millions of people would be involved here?

RICHARD ALLEY: That’s my understanding is that, yes, when we start looking at three feet, six feet, or more, there’s a lot of people close to that. And you start thinking about what did Hurricane Sandy do to the subways in New York, and a rise that would be close to the size of what was going into the subways, all by itself without help from a storm.

IRA FLATOW: OK. So that’s Antarctica. I’ve heard that if the entire Greenland ice sheet melted, the whole thing, that sea levels would actually be lower around Greenland. Is that possible?

RICHARD ALLEY: Very close to it. So there’s an interesting nuance here. As you know, all bodies are gravitationally attracted to all other bodies. You and I are attracted very, very weakly because we’re small and far apart. But Greenland’s ice or Antarctica’s ice is so big that it actually attracts the ocean to it. And so, if you melt a body of ice, the sea level rises on average everywhere, but that water that was pulled to the ice sheet relaxes away.

So, in Antarctica, for example, if you melted West Antarctica’s ice, it raises the global average sea level about 11 feet. Right next to the Antarctic ice, sea level will actually fall, and in Washington DC sea level will go up about 13 or 14 feet.

IRA FLATOW: 13 or 14 feet? Would that in New York too?

RICHARD ALLEY: Yes.

IRA FLATOW: Go The whole East coast?

RICHARD ALLEY: The Northern hemisphere gets more than the average. The Southern hemisphere less from Antarctica and vice versa for Greenland.

IRA FLATOW: You know climatologist Jim Hansen has been very outspoken about this for a number of years. This sort of backs up what he’s been saying, does it not, validates his position?

RICHARD ALLEY: I think it is fair to say Jim has been ahead of us very often and he is raised a lot of warnings about the possibility of rapid sea level rise and this is putting some physics behind the things that he’s been thinking about.

IRA FLATOW: You know, you have said, I’ve seen videos on YouTube of you, said in the past that you were a Republican but one who obviously contributes to our understanding of global climate change and you are puzzled by why global warming has been a political hot potato.

RICHARD ALLEY: It flabbergasts me some days. The first time I testified to the subcommittee of the US Senate, it was chaired by a Republican who wanted to put in place this sort of price signal conservative solution that would move us forward and improve the economy as well as the environment.

IRA FLATOW: That’s what would happen. [INAUDIBLE] what happened, why it became political. People like to blame Al Gore for this because he was a polarizing quote unquote figure. Do you buy that?

RICHARD ALLEY: It is possible that the blame rests with me, with us as scientists, at some level that rather than us stepping up and doing the job of teaching what we know, that we waited for someone like Mr. Gore to do the job. And that because he comes from one side, that did put some people off. I could tell you a lot of stories of why.

What I do know is that the science is very, very strong and, in addition, the evidence is very strong that if we take what we know, and what we believe in, and where we want to go, not only do we clean the environment, but we improve the economy.

IRA FLATOW: Are you surprised that this is not an issue knowing what you know and the time that we know is almost around the corner. In times of less than a century. That it’s not a political issue in the campaigns this year?

RICHARD ALLEY: My suspicion is that the attention span has gotten so short for people in a different piece of the media then your show, that this one doesn’t make a good sound bite and then I fear that many of the discussions have been reduced to things that would not be– your show does things much better than that.

IRA FLATOW: Thank you. We try. Sometimes it’s not really hard to do that. Unfortunately. Let’s talk about ice sheets because I’m very fascinated by ice. I was in Antarctica many, many years ago, back in 1979, and I saw a lot of ice down there. What would you really want to know about ice that’s still a mystery to scientists like yourself? Because ice is sort of a magical item isn’t it? It behaves like rock sometimes. It’s like liquid water.

RICHARD ALLEY: Oh, yeah and there’s a huge amount that I want to know because it’s fun, and it’s fascinating, it is interesting, and then there’s a huge amount that I want to know because we actually owe it to the public to tell them how likely this is and how fast. And sometimes those overlap.

Right now, the big issues include if you go in a ship, when you were in Antarctica, you either flew over, you came in a ship, and if you look down at the sea floor under you, you would have seen giant piles of mud that were left over thousands of years when the ice ended at one place and then nothing.

And the ice would have backed up way fast in a big hurry and then stopped somewhere else. The ice is like the military holding the high ground and then retreating off the valley to the next high ground. And right now, the ice we’re most worried about is hanging onto a piece of high ground its fingernails. And we would love to know exactly what’s needed to keep it there or what might push it off.

IRA FLATOW: Because as you intimating before, there’s sort of a wall that’s keeping the main sheets of ice from going into the ocean and if we lose that, that would slide right in.

RICHARD ALLEY: That’s right. There’s a lot of this, has in it thresholds. You push it a little bit and not much happens, you push it a little more and you cross the threshold and something huge happens. And a lot of this has in it breaking things. And breaking things– you can do the experiment in your head. Imagine a room full of people with ceramic coffee cups on a hard floor and on three everyone in the room tosses a ceramic coffee cup up in the air and they fall on the floor. And what happens? That one breaks, and that one chips, and that one bounces, and that one cracks, and that one blows into smithereens. Predicting when things will break and how they will break is hard. And were trying to predict one coffee cup.

IRA FLATOW: Would it be fair to say that Greenland is sort of the Antarctic of the north? They’re basically very similar in ice.

RICHARD ALLEY: There’s a lot of similarities there. We are cautiously optimistic that most of Greenland can’t fall in the ocean as rapidly as pieces of West Antarctica can. When these giant lakes break through the ice and make the huge floods in the drama, there’s bumps underneath. Its like Greenland is spreading across a waffle iron and it can’t fall off very easily. Pieces of Antarctica are more like spreading across a greased griddle rather than a waffle iron.

IRA FLATOW: And so going to both places you learn a little bit more about the waffle iron and the griddle.

RICHARD ALLEY: Absolutely. And we really do need both places because there’s things going on in Greenland now which is a little warmer that may be the future of Antarctica. And we can see what’s happening in Greenland and translate that into what might happen in Antarctica.

IRA FLATOW: It’s pretty scary, Dr. Alley, I’ll tell you, it’s pretty scary.

RICHARD ALLEY: But there is some optimism there. We still might win this one.

IRA FLATOW: All right. Well I’m going to take your optimistic route, OK? Richard Alley is a professor of geosciences at Penn State University. And any teachers listening now, how to bring climate science into the classroom, we have a team of experts together for a live online panel next Tuesday, April 5, at ScienceFriday.com/climateclassroom.

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