MS. MELISSA ROSSThanks for joining us. I'm Melissa Ross of WJCT in Jacksonville, Florida, sitting in for Diane Rehm. She'll be back next week. The earth's great ice sheets are shrinking at an accelerating rate, but just how quickly is uncertain and it has significant implications for our ability to cope with sea level rise. For this month's Environmental Outlook, the latest research into the earth's melting ice sheets.

MS. MELISSA ROSSJoining me from KUCI in Irvine, California is Eric Rignot, professor of earth systems at UC Irvine, from University Park, Pennsylvania, Penn State glaciologist Richard Alley and from Paris, Chris Mooney of The Washington Post. We invite you to join the conversation with us as we take your comments and questions throughout the hour. Give us a call, 1-800-433-8850. Send us your email to drshow@wamu.org.

MS. MELISSA ROSSOr join us on Facebook and Twitter. Richard Alley, let's begin with you. What are we talking about when we say the earth's ice sheets? How many are there and just how big are they?

MR. RICHARD ALLEYSo they're huge. We have one big one sitting on the island of Greenland and we have one huge one split into two parts in Antarctica. If they all were to melt and all their water were to go into the ocean, the ocean would rise about 200 feet. So they are big. They're two miles thick in the middle and a continent wide.

ROSSAnd what you just said, that scenario, if they were all to melt, that level of sea level rise, this nightmare scenario is, of course, one that is the absolute worst case scenario, one that -- Eric Rignot, let's bring you into the conversation, you and Richard don't necessarily agree on the timetable for ice sheet melt, but in general terms, of the three major ice sheets, some are more stable than others, correct?

MR. ERIC RIGNOTYeah. We tend to separate the parts of the ice sheet that are resting on the bed below sea level from part of the ice sheet that has a bed above sea level. We've known for a long time that the parts that are resting on the bed below sea level are more sensitive to climate change.

ROSSRight. And the massive ice in the Greenland ice sheet has begun to decline, your research showing, from 1979 to 2006. Summer melt on the ice sheet has increased by 30 percent. Greenland now experiencing an average net loss of about 303 billion tons of ice every year. Can you paint a picture for us what that means for cities, coastal cities particularly, around the world?

RIGNOTYeah. So Greenland contribute approximately the equivalent of one millimeter per year of sea level rise, actually a little bit less than that. And that amount is increasing every year. Of course, there's a little bit of variability from year to year on top of that. So in a cold year, it's not going to increase as much as in the warm year. And one millimeter doesn't sound like much, but of course, it's -- the numbers are going up and it's going to go on for decades to centuries to come.

RIGNOTSo even though you may not see the effect on the year by year basis along the coastline, along the long term, you know, we're looking at a meteor sea level rise from melting ice sheets by the end of the century or possibly more.

ROSSAnd Chris Mooney, energy and environment reporter with The Washington Post, it's the uncertainty of the timetable that is vexing scientists so much, isn't it? Whether it's a matter of decades or centuries, as we look at the rate of melt. Can you talk a little bit about that?

MR. CHRIS MOONEYSure. I don't think that scientists know at present the rate at which this is going to unfold. Certainly, every time I ask them, they say that there is a great deal of uncertainty. They tend to mostly say that this is something -- especially if you're talking about total loss of any one of these ice sheets like, say, West Antarctica, they will tend to say hundreds to thousands of years. I do know that there is some concern that they don't fully understand all of the processes involved that occur once you start to destabilize one.

MR. CHRIS MOONEYAnd there's some concern that it may be faster. I think you actually should ask the experts we have, though, and I'd be interested to hear what they say.

ROSSLet's go back to Richard Alley on that. Richard.

ALLEYYes. So there's things that we really know. You make it warmer and ice melts. And we're making it warmer and ice is melting. The future holds sea level rise from the ice sheets with very high confidence. And the uncertainties are mostly on the bad side. So let me do an analogy, if I may. If you were one of these poor people who has to drive to work, what you really expect is to get stuck in traffic at a time when you can't listen to "The Diane Rehm Show."

ALLEYThe best thing that can happen to you is no traffic and a good radio and the worst thing that can happen to you is you get run over by drunk driver and you're dead. When we look at the ice sheets, we see sea level rise coming from the ice as it warms. It might be a little less than we expect. It might be a little more and there could be things that go fast that could make it a lot more and a lot faster.

ROSSEric Rignot, as you have been quoted as saying recently, right now, as climate talks, landmark climate talks are underway in Paris, as the world's nations are trying to reach an agreement not to warm the planet by more than 2 degrees Celsius, you've suggested that even that target of 2 degrees may not be aggressive enough. Why not?

RIGNOTYou know, I think we have solid Paleo records now that show that when the temperatures in the past were about 1 degree to 2 degree above preindustrial, sea level was 6 to 9 meters, 18 to 27 feet higher than present. That does not necessarily mean that it is going to happen each time the earth warms up by 1 degree, but it's a solid indication that by locking the earth into a temperature regime 1 to 2 degrees above preindustrial, we are likely to experience a 6 to 9 meter sea level rise, which means that part of Greenland, part of Antarctica will melt.

RIGNOTThat does not provide a time scale, though. We don't know from these records exactly how fast this can happen. So we are sort of already here. We're already at the 1 degree above preindustrial, running very quickly into the 2 degrees. And, frankly, the 2 degree landmark is a little bit of a landmark made out of thin air. It's like a good objective down the line to gather up and do something significant, but if you look at the signs of a 2 degree warming of the planet, things don't look that good.

ROSSAnd you've tried to look at worst case scenarios, be a bit of an outlier in your field, looking at the absolute upper bounds on how fast these ice sheets could melt and how fast the seas could rise. You've said you don't want to come back in 50 years and regret being too conservative in your estimates, correct?

RIGNOTWell, yes, because in terms of sea level rise, you're not really interested in the middle range scenario. You just want to know -- if you're a city planner and you want to build levies to protect the city, you want to know just how bad things can be. So that's a little bit of our concern for ice sheets. We just want to be able to have a good handle on how bad things can be. So like Richard said earlier, we have a pretty good handle on monitoring an ice sheet melting from warmer temperatures and warmer ocean temperatures.

RIGNOTWe don't have a very good handle on predicting how fast it can start discharging icebergs into the ocean. The dynamic part of the ice sheet, the glacier flow and the acceleration of ice into the sea, we have a good understanding of the physical processes involved, but we don't have a good numerical modeling of that that can really rely on. It's a little bit like we know where the fault zones are and we're trying to predict the next earthquakes.

RIGNOTWe know there's going to be some earthquake coming up, but we can't exactly predict when and how big they're gonna be. It's a similar explanation for ice sheets.

ROSSChris Mooney, you wrote recently that we've found out about -- that what has been learned about the Antarctic ice sheet could be the biggest climate change story of the last several years. Why is that?

MOONEYYeah, I think -- this is why I focus a great of my coverage on it. So give you a little context. In 2013, the United Nations intergovernmental panel on climate change released its latest sort of mega report synthesizing everything and they certainly gave us plenty to worry about and they said that there's a high level of certainty that humans are causing global warming. And then, they said in there that, you know, at the high end, seas could rise maybe a meter by the end of this century.

MOONEYAnd it was actually after that that our other guests, among others, published research suggesting that there might be -- this is -- Richard Alley published this, that there might be processes that models don't take into account. And Eric Rignot and others published the idea that the West Antarctica ice sheet, in particular, might have reached a point of instability. That was all after the scientists of the world assessed our state of knowledge.

MOONEYSo it's in those last two years since we got our download of the state of the science that we learned a lot of things that seemed really surprising and that tended towards making people think, wait, this process might be already started.

ROSSRichard Alley.

ALLEYYeah. So some of your listeners have probably seen spectacular video of these giant icebergs rolling off of the front of glaciers in Greenland and shaking the ground so much that you can hear it on a seismometer in South Dakota. And those things are sort of half a mile high or something. They're huge. They're just -- it's really amazing. But if a particular piece of West Antarctica should retreat and it should retreat notable, which is possible, and this is based on work in part done by Eric, it would make a cliff that's a lot bigger than that and capable of changing a lot faster.

ALLEYAnd that's really sort of disturbing and it's also something that we worry about that it could go really fast. And based on the physics -- and as Eric mentioned, doing things that break, earthquakes and things like that, is really hard. And so whether exactly how fast will it break, exactly how fast will it crumble is hard.

ROSSAnd as we continue this discussion looking at the melting of the globe's ice sheets, we'll bring you into the conversation. Stay with us.

ROSSWelcome back. I'm Melissa Ross of WJCT in Jacksonville, Florida, sitting in for Diane Rehm today as we discussing the rapid melting of the ice sheets in Greenland and Antarctica. We're joined by Eric Rignot, professor of Earth system science at UC Irvine, Richard Alley, professor of geosciences at Penn State University and Chris Mooney energy and environment reporter, Washington Post. We'll go to your calls and comments in just a moment.

ROSSAnd talking about these different rates of melt and predictions of sea level rise can feel very abstract at times. Right now let's welcome Benjamin Strauss, vice president for sea level and climate impacts at Climate Central. And Ben, tell us a little bit about what you've done to help people understand in real terms what this might mean for them on the ground in their cities.

DR. BEN STRAUSSWhen these ice sheets crumble, and the sea level rises, that affects our global coastal cities and where people live. And while we can't put an exact time stamp on when we'll see different amounts of sea level rise, we can at least -- we can at least estimate how many people live on the land that the water would cover and give people a sense of the extent of this impact. And so for an example of that, if we were to put enough carbon into the atmosphere to warm the planet by four degrees Celsius, a little bit more than seven Fahrenheit, more or less the path that we are on right now, we could expect at least enough sea level rise to cover land where more than half a billion people live today, actually closer to 10 percent of the whole world's population.

DR. BEN STRAUSSAnd if we limit warming to two degrees Celsius, we would be talking about less than half of that.

ROSSAnd so you've created an interactive global, Mapping Choices. Anyone can type in their zip code and look at where their city is. You've given different cities different lock-in dates. Can you explain what you mean by a lock-in date?

STRAUSSYes, so one of the things we can do, that we have done in our analysis, is to figure out the elevation for each city in the United States that half of the population lives beneath. And we take that elevation and we ask when will have -- will we put enough carbon dioxide in the atmosphere to lock in enough sea level rise so that it rises above that elevation. And we can go decade by decade down different carbon pathways and say that in year X, we will have locked in enough sea level rise to eventually put half of Jacksonville, Florida, for example, below water, or by year Y another city or by year Y under a different pathway. It might be sooner if it's a higher carbon emissions pathway, or it might be later if it's a lower emissions pathway.

ROSSAnd as we've been hearing, it can be difficult to understand the rate that the ice sheets are melting. There's such a big range of predictions. So what rate did you use to create your maps?

STRAUSSWell, we didn't use a rate. We just used the amount of sea level rise. I like to think of as if I had dropped a large block of ice in a warm room. All of us would immediately know how much was going to melt, all of it, right. That's easy to tell. It's much harder to predict the rate minute by minute by minute how much it's going to melt. So we skipped the rate part and focused just on how much.

STRAUSSAnd we have more confidence in how much will melt than the rate scientifically because we can look back at the last three million years of geologic history, which has been populated by a series of ice ages and warm periods between them, and for the warm -- for several of the warm periods, we have good estimates of global temperature, and we have good estimates of past sea levels. We plot those points. We have a relationship, and we have a good sense of what the sensitivity of sea level is to warming.

STRAUSSSo we skip how fast and focus on how much, and therefore this becomes a question of legacy. Although I can't tell you exactly when these cities will have these problems, we are making these decisions right now, in the past few decades and in the coming few decades, about whether we will be able to have a Miami in the future or not, whether we will...

ROSSBecause Miami is past its lock-in date, according to your projections, correct?

STRAUSSThat's right, past or imminent.

ROSSSome cities still have time, according to Climate Central.

STRAUSSThat's right. So there -- and there's -- it depends on the city, but for example for New York City, if we pursued a very aggressive carbon-cutting regime, we could prevent sea level rise. We could basically save the land where more than one and a half million people live today.

ROSSBenjamin Strauss, vice president for sea level and climate impacts at Climate Central, thanks so much for being with us.

STRAUSSThank you.

ROSSSo Eric Rignot, when we look at the Climate Central map, that brings it home to people living in their individual cities, does it not?

RIGNOTYes, it does, and that's a very important point about sea level is that, you know, as glaciologists, we're looking at what's happening in the polar regions, and the polar regions are melting, and the rate of sea level rise is going to vary from place to place. It's not a global number that we can use everywhere. There's local variation, local conditions that make it so that in some places it's going to rise faster than others. So that's an important factor because people want to know exactly what's going to happen in their own neighborhood because it's going to be directly affecting them.

ROSSLet's go now to Steve in Bloomfield Township, Michigan. Hello, Steve, good morning to you.

STEVEHow are you today?

ROSSGreat, thank you. Thanks for calling.

STEVEFirst I have a comment, and then I'd like to ask a question.

ROSSOkay.

STEVEMy comment is, you know, in my opinion Climate Central, just they're fear-mongers about the environment, and they have a political agenda. The second statement is of course in Paris, all these countries showed up because the largest counties are going to hand out billions of dollars to them, and of course they're going to show up when somebody's giving you money. And the third thing, I'd like to add a little science to this discussion and tell people to go to nasa.gov to look at the article from October 7, 2014, which states that Antarctic sea ice reaches new record maximum. So you're talking about sea ice is melting when actually the largest ice sheet on the planet is at its maximum ever recorded. So just do your own searches on Google, and you can avoid all these fear-mongering, climate-change nuts. That's what I'm saying. I...

ROSSSteve, yeah, thanks for the call. I'm glad he brought that up. Richard Alley, there are conflicting studies, and there is a study out there saying that the ice sheets actually are increasing. What about that study? Can you respond to that caller?

ALLEYSure, so first of all, the mentions, as Steve mentioned, sea ice, so frozen ocean, water around. And just so we've very clear, there is land ice, which when it melts will raise sea level, and there is sea ice, which is already floating. This maximum in Antarctic sea ice is possibly a result of warming. We have known for a very long time that in the Arctic, when you make it warmer, that sea ice melts. And we've also known that in the Antarctic, it's so cold that there still is the ability to freeze ocean near the ice sheet, but if you start melting the ice sheet faster, you add freshwater to the ocean, which can freeze more easily.

ALLEYAnd so the models have been very consistent in saying the Arctic sea ice should shrink with warming. It is shrinking with warming. The Antarctic sea ice, the models have actually disagreed whether it should grow or shrink, but with a possibility of growth before shrinkage, you're seeing a little growth. So this is all completely consistent with understanding. For the land ice -- so this one, so very clear, the changes so far in the ice sheets have been fairly small. A lot of this is work done by Eric Rignot, so I'm quoting him, but averaged over the 20 years leading up to the most recent IPCC report, the ice sheets were contributing 0.6 millimeter a year of sea level equivalent.

ALLEYThat means it would take 100,000 years for the ice sheets to melt completely. That is the equivalent of me going on a diet and losing one-third of one potato chip in a year. And they measured this, and they did it with high confidence. But if you look at the whole range of studies, there is a little difference among the different techniques. This recent paper to which you're referring is an outlier. There's a very strong agreement, and then there's a couple of outliers. It's real science by good people doing a hard thing, but it does look like Antarctica is still shrinking.

ROSSEric Rignot, are you in agreement with Richard?

ALLEYAbsolutely. I think he said everything right. We have to take also some sort of long-term perspective here. So we have about 20 years of observations of the ice sheet, very, very precise observations. We have a record that extents a little bit more like 40 years back, using some of the earlier satellites. And we are sort of using that to project what may happen next. As Richard mentioned, the level of melting of the ice sheets in the global seas is very small compared to the total reserve of ice in the polar regions. On the human scale, it is not that small. We're talking about billions and billions of tons of water, extra water discharged into the ocean.

ALLEYWe also know that what we're seeing is just sort of the beginning of the melting away of the ice sheets. We know that this rate of melting of the ice sheet is not going to stay steady with time. It's going to keep increasing in the future, especially if we continue warming the climate in sort of an burn as much as we can scenario. So it's really important to take a long-term perspective on this because this kind of experiment that we're doing with the Earth system, warming it up and looking at the ice melt, we're only going to be doing that once, and we don't want to wait until we have a six- to nine-meter sea level rise to tell you hey, I told you this could happen, right.

ROSSAnd Chris Mooney, here's a comment coming into the show from Diane's website. Our last best chance at doing something about climate change is happening in Paris. The window of opportunity for doing anything before a chain reaction sets in that more or less spirals out of control and dooms our planet to a fate that will negatively affect the quality of life for generations to follow is closing fast. Is there a sense of that -- not doom but that sense of urgency at the Paris talks?

MOONEYYes, I'm here in Paris covering the talks, and I would say for sure that the research we're talking about now is having an influence in the negotiations. And I can just get real specific. There's been for a long time a coalition of small island nations. They are the most worried about sea level rise. They have for a long time held the position that warming the globe needs to be limited to 1.5 degrees Celsius, precisely because they think that beyond that they are going to lose large amounts of their territories or in some cases maybe lose all of their territories.

MOONEYSo in the -- but big industrial emitters have generally held out for two degrees Celsius of warming as the sort of maximum. What we're seeing in Paris now is actually we're seeing that the 1.5 target is drawing more and more attention, and actually the United States, even France, some of the big countries are saying that, you know, if we can get the 1.5 degrees, we should. They're starting to mention it. They're starting to talk about it. The message of the small islands is starting to become more and more influential, and I think that is principally because of the kind of research that we're talking about right now.

ROSSAnd I'm Melissa Ross, host of First Coast Connect, WJCT Jacksonville. You're listening to "The Diane Rehm Show." If you'd like to join us, call 800-433-8850. Send an email to drshow@wamu.org, or find us on Facebook or send us a tweet. And let's go now to Jeff in Houston, Texas. Hello, Jeff, good morning.

JEFFHi, good morning, thank you for having me on. I have a definite interest in what's going on because I live in Houston, Texas, which is not known for being very high above sea level, and also because we have a very vocal senator from Texas who does not believe in climate change at all and in fact held hearings yesterday on Capitol Hill parading experts in front of Congress to support his position that there is no such thing as global warming or climate change.

JEFFI think what's serious, though, is that people don't realize what's at stake here. And what we're looking at, for example if just the Antarctic ice sheets melt, it will cause a loss in Texas of 15 percent of its big territory. The Gulf Coast will be more than 100 miles inland from where it is now, which will completely eradicate the city of Houston. On a bigger scale, almost all of Louisiana will be gone, the Gulf Coast will go as far north as Memphis, and all of Florida will be gone.

ROSSJeff, thanks for the call. And let's go now to Richard Alley. Richard, when people look at how sea level rise will affect their city, their state, and they look at the politics of this. As someone who studies the science, perhaps you might not want to comment about the politics, but what about his comment about the hearings on climate that tend to go on regularly here in Washington, D.C. Your thoughts about the politics?

ALLEYYeah, I have participated in a hearing on occasion. It's not always an entirely pleasant undertaking, and it does seem that it's a little bit set up to give an idea that there is an argument about things that there really is not too much of an argument about. So if one looked at the hearing that happened yesterday, there were some real scientists participating, and there was a selection of the most skeptical of scientists about the seriousness of this issue and one representative from somewhere towards the middle and I think no one towards the most alarmed side of things.

ALLEYAnd so if you looked at that hearing, you might have somehow had the idea that there are two sides of this, and that's maybe the biggest distortion in the whole discussion. Science is the best that we humans know, and within the range of science, there are people who are more concerned, there are people who are less concerned, but there are not two sides. CO2 is a greenhouse gas from physics. We are raising it from physics. This will have an influence on the climate that can't be avoided, and we are interacting with the climate. And there's no two sides of that.

ALLEYAnd so I think if we were to get back to the reality that science has a range of views, but they are centered around science, we probably could have a much cleaner path to the future on this.

ROSSAnd we will continue this discussion as we look at the rate of melting ice sheets in Greenland and Antarctica. We'll be taking your comments and questions throughout the hour. Give us a call. 800-433-8850 is the number to join us. We'll be back in a moment. I'm Melissa Ross, sitting in for Diane Rehm, and send us your emails, as well, drshow@wamu.org. Or you can join the conversation on Facebook and Twitter. Back in a moment.

ROSSWelcome back. I'm Melissa Ross of WJCT, in Jacksonville, Fla., sitting in for Diane Rehm today, as we discuss the melting of the ice sheets in Greenland and Antarctica. We continue the discussion with Eric Rignot, professor of Earth systems science at UC-Irvine, Richard Alley, professor of geo sciences at Penn State University and Chris Mooney, energy and environment reporter at the Washington Post.

ROSSEric Rignot, I'd like if -- you to address, if you could, when people are skeptical of climate science, explain a little bit about the laborious process that goes into your research and how you arrive at these scientific conclusions.

RIGNOTYeah, we arrive at these scientific conclusions using a whole range of instruments. And, in fact, Richard was mentioning some of the studies that have been compared in the past. We have many different methods to look at the ice sheet melting. We have, like, three different, totally independent ways to look at the rate at which the ice sheets are melting. And we've gone through the exercise of comparing the numbers, looking at the uncertainties.

RIGNOTThis is a gathering of groups from all over the world that sit down and brainstorm their numbers and how they agree. And at the end of the day, we have a remarkable agreement. We've made tremendous progress in measuring how the ice sheets change with time. Back in the 1990s, we didn't have a lot of very good tools to do that. And now we are very well equipped with satellite missions, airborne platforms, people on the ground.

RIGNOTSo that in terms of ice sheets melting and how they change with the time, we know that extremely well. It's not really the question. The question for us is to sort of use that knowledge to build up better numerical models so we can project what's gonna happen in the next decades, in the next centuries.

ROSSAnd in fact, to project into the future, you often reference an event in the distant past, about 14,000 years ago, an event called Meltwater Pulse 1A. Can you tell…

RIGNOTYeah.

ROSS…us a little bit about the significance of that?

RIGNOTWell, the significance of that is that it gives us a little bit of pointers about how fast a sea level could possibly rise. As I mentioned earlier, if we look at the current trajectory of the ice sheets, how fast they're melting and how fast the melting is increasing with time, if we continue on that same pace we are heading for a meter sea level rise per century. But we very well know that the ice sheets do not behave in a sort of linear fashion, business as usual.

RIGNOTThings are likely to go a little bit faster with time. And the studies of rapid melting of the ice sheets 14,000 years ago suggests that sea level could rise as fast as four meters per century. So we get some boundary here in terms of what may happen in the coming century. We know that we're kind of on pace already for a meter per century, but sort of worst-case scenario could be as fast as 4 meter per century sea level rise from rapid decay of the polar ice sheets.

ROSSRichard Alley, you are a little more conservative in your projections. Yes?

ALLEYWell, no.

ROSSNo?

ALLEYSo the difference between what we think is most likely and what's the worst case. And this comes back, if your listeners have been with us, to my analogy to the commuter. If you are a car driver you do not expect to be killed by a drunk driver, but you actually have insurance and anti-lock brakes and you fasten your seatbelt and you put your kid in a car seat and you support police who out looking for drunk drivers and you support Mothers Against Drunk Driving and you take a lot of actions to try to avoid the disaster because it's -- would be so consequential.

ALLEYWhen we look at the ice sheets, as Eric was saying, we see the possibility of really big, fast -- you might call it disastrous sort of sea level rise. You know, if you were a small island state and looking at loss of west Antarctica in a century, you probably would call that a disaster. And so the most likely rise has costs. And the economics are very clear that if we deal with this wisely it helps the economy. But the worst possibility is still pretty bad.

ROSSHere's a tweet from Phillip. "Hasn't the Earth gone through warm and cool cycles for millennia?" What about that commonly raised point, when it comes to this discussion?

ALLEYYeah, if I may follow on. We've always had natural fires, but we have arson. And we sort of hope our arson investigator knows about natural fires. And the truth is our arson investigator probably appreciates fire more by knowing how powerful it is and how damaging it can be by looking at the past. The more we look at the history of climate, the more we see that climate has changed, that climate has changed because of CO2 changing more than anything else, that that has affected living things.

ALLEYAnd we look now -- and recently nature has tried to cool it off a little bit, but it's gotten warmer because we are cranking up CO2. And so the nature is always changed when you run it through the whole science, comes back to we are making a really big, fast change to the system. It is very, very likely to have huge consequences for living things, including us.

ROSSLet's go now to Dave, in South Bend, Ind. Hi, Dave. Good morning, Dave.

DAVEHello. Jacques Cousteau, the great French scientist and explorer, gave a scenario about coastal flooding that was pretty serious. He said that as the coastal areas are flooded, all the chemicals -- you see, we're forgetting about the chemicals that are in the ground and on the ground, lawn chemicals, agricultural chemicals, automotive, these will get leached out of the ground and scoured off the ground as the tide goes out. And eventually the oceans will become so toxic you'll have a massive marine die-off.

ROSSEric Rignot, another Frenchman. What about his question and his comment about Cousteau's research?

RIGNOTWell, I'm not a specialist of this chemicals leaking in the ocean, but it's true, generally speaking, that the consequences of sea level rise go a little bit beyond just getting flooded up to your knees. There's one problem that has not mentioned, is the displacement of population. There are some places like in Miami if people have to move to a different place, they're gonna pack up their stuff and go inland and buy another house.

RIGNOTThere are places like Bangladesh, where people have no place to move inland to and they're gonna have to go to another country, they're gonna have to ask the other country to host them and take care of them while they try to establish a living. And we know from what's happening today around various borders that this is a very difficult situation for everyone, to help each other, help refugees and deal with this. So it's not only affecting the countries directly affected by sea level rise, it's affecting also their neighbors, who are gonna have to help them out.

ROSSTo Jane, in Laurel, Del. Hey, Jane. Good morning, Jane.

JANEGood morning. I believe that we are destroying our planet at a greater rate than it can recover itself. But I've been curious about whether these other planets that we're exploring for life, is there any evidence that they were ever inhabited and perhaps they destroyed their planets the way we're destroying ours.

ROSSWell, hard to answer that question. But, Richard Alley, your work is informed certainly, as is Eric's, by the conviction that continuing on the course we're on will cause harm to the planet. Yes?

ALLEYQuite clearly. There's a -- if you were to sort of take the entire body of research that goes from science through what it means to us, to economics and so on, the outcome is very, very clear. Which is if we adopt wise policies that respect the science, not only do we get a cleaner environment, but we get a bigger economy with more jobs, with greater national security that is better for the golden rule.

ALLEYAnd so this is knowledge that can be used to help people in very fundamental real ways. And in big ways, yeah, trillions and trillions and trillions of dollars in the economy are there to be made with wise policies based on very strong and very sound economics that we can get to chapter and verse on, but the work is done. It's there.

ROSSAnd how hopeful are the both of you that the talks underway in Paris can bring about that sort of paradigm shift?

RIGNOTWell, I want to add to what Richard said, that there's a lot of negativity around controlling climate change, which I don't quite agree or understand. I think dealing with these issues of carbon emissions, reducing them and moving to cleaner energies and eventually trying to develop some technologies to suck back in all these extra CO2 released in the atmosphere, we sort of passed a point, a threshold by which we say we are not in a safe climate regime anymore.

RIGNOTWe have to go back to what it used to be. We can actually build a better world. A world that uses clean energy, that creates new jobs, that uses the planet in a more sustainable fashion. There's a lot of positiveness in all of this. It's something that everybody should aspire to work on. And I know for a fact that a lot of the young people, the young generation in our nation care a lot more about these issues. To them it makes complete sense to move in that direction.

RIGNOTIt's a little bit more difficult for the older people, like me and Richard, to change our habits. We're trying, but it's a little bit harder for us because we've been used to a certain way of living. But this new way of living that we're talking about is a good thing.

ROSSHere's an email from Chris. "Yes, long-term projections about sea level rise have some uncertainty. Please have your guests comment about the impacts of sea level rise occurring now." What about that, Richard Alley? As we've been discussing, it's very difficult to predict the rate of sea level rise and ice sheet melt over time. But as we look at 2015, we can assess some impacts right here, right now. Can't we?

ALLEYYeah, I was trying to walk around the Tidal Basin last spring to see the cherry blossoms. And the tide was over the sidewalk and it was coming up close to the roots of the cherry trees. And all up and down the East Coast we're seeing what they call nuisance flooding, which is -- it used to be that it took a storm, as well as a high tide to get up onto the streets. And now just the high tide is doing it. So we're seeing the impacts. And there are certain places, either the water gets into the subway or it doesn't.

ALLEYAnd a very small difference in sea level can make a big difference in how people are living and what's going on. And so we are already seeing impacts. But we're seeing impacts way down on the slow, expected sort of rise. In the worst-case scenario, if west Antarctica goes in the ocean, compare it to Hurricane Sandy. Hurricane Sandy or superstorm Sandy or whatever, brought, you know a few extra feet of sea level to a small piece of one coast for a few hours, and it was sort of consequential. West Antarctica potentially brings that much water to all the coasts of the world for a very, very long time.

ROSSI'm Melissa Ross, sitting in for Diane Rehm. And you're listening to "The Diane Rehm Show." Chris Mooney, given that we are already seeing the impact of sea level rise, how much is that coming up in the climate discussions underway now in Paris?

MOONEYOh, I think that -- so there are many assorted impacts of climate change and they are all in play here. What's happening is sort of the hardest thing for humans to achieve, which is to get all the countries of the world to agree about how their futures are gonna go and be on the same page about that. And to do it based on a gigantic body of science, which involves not just melting ice and sea level rise, but it involves obviously, you know, fears about temperature extremes, fears about changes to weather or how that is going to affect really vital things like agriculture and water.

MOONEYThey are assessing all of these things. There's just no doubt that there is a really great level of concern, greater than there has been at past meetings where people tried to achieve -- where everybody tried to achieve big agreements. I think that the tone is really -- has this level of concern. And, again, I would argue that if there's -- there are many factors that are driving the higher level of concern now, including the fact that warming just keeps going up and we're in the midst of what is very likely to be the hottest year ever recorded, but I think one of them really is, again, the research we're talking about.

MOONEYAnd certainly the fact that, you know, just last -- I think it was just last month and Eric Rignot can tell you more about it, they just found another, you know, what looks like a very important instability in part of Greenland. So, you know, this news has been coming fast. And it's being noticed by negotiators and leaders all around the world.

ROSSEric Rignot, what about that instability that Chris just mentioned?

RIGNOTYeah, it's a part of northeast Greenland, where we have an ice stream that goes for hundreds of kilometers inland. We've been looking at this ice stream for many, many years. It reaches all the way into the ice sheet to Greenland Summit. And it discharge ice in the northeast corner, in the far northeast corner of Greenland, where it stays cold and dark most of the time. And in the last few years we've seen the flooding extension of that glacier disappear very quickly. And the glacier's starting to bring these big icebergs, Richard was talking about before, faster and faster to the sea.

RIGNOTAnd this sector is one of the major floodgates of Greenland. It's an area where a lot of the ice that resides in the basin is below sea level. It's prone to rapid change. And we think that we saw a transition in 2012 in that sector that says that floodgate -- somebody opened that floodgate and ice starts to rush out. It's not rushing out as fast as what we're seeing in west Antarctica, but it's a little bit of a red flag that's been raised in northeast Greenland.

ROSSAs the red flags continue to pop up, Richard Alley, very quickly, there is still uncertainty about the rate of melt. What can you leave listeners with about the timetable, since scientists are still trying to get their arms around that data?

ALLEYYeah, warming melts ice. We face sea level rise in a warming world. The numbers that you often see for what is most likely are on the optimistic end of what is possible. So the less you trust us the more worried you might be.

ROSSWell, we appreciate all three of you joining us for a fascinating discussion that affects so many millions of people. Thanks for being with us. Eric Rignot, professor of Earth system science at UC-Irvine. Richard Alley…

RIGNOTYou're welcome.

ROSS…professor of geo sciences at Penn State. And calling in from Paris, Chris Mooney, energy and environment reporter with the Washington Post. Thanks so much for being with us today as we discuss fascinating research into melting ice sheets in Greenland and Antarctica. We so appreciate your calls, your tweets, your comments on Facebook. It's been a pleasure to sit in for Diane Rehm this morning.

ROSSThanks so much everyone for being part of the program. I'm Melissa Ross, host of "First Coast Connect," WJCT Public Broadcasting, in Jacksonville, sitting in for Diane. And thanks for listening today. I'll be back tomorrow and Friday. And thanks for being with us. Keep emailing the show tomorrow at drshow@wamu.org and make sure to join the conversation on Facebook and Twitter, as well. Really appreciate it everyone being on the show today.