MS. INDIRA LAKSHMANANThanks for joining us. I'm Indira Lakshmanan sitting in for Diane Rehm. She's recovering from a voice treatment. Just days before a massive snow storm hit the east coast, scientists announced that 2015 was the world's hottest year on record, far surpassing the previous record holder, 2014. Last year also brought some notable extreme weather events, including killer heat, drought, flooding and storms.

MS. INDIRA LAKSHMANANJoining us to talk about what the global temperature spike means for weather patterns and the health of our planet in the near and long term, from the studios of NPR in New York, Lisa Goddard of Columbia University's International Research Institute For Climate and Society, and Gavin Schmidt, climatologist and climate modeler for NASA.

MS. INDIRA LAKSHMANANFrom the studios of WCQS in Ashville, North Carolina, Deke Arndt of NOAA's climate monitoring branch and braving the aftermath of a snowstorm to join us in our Washington D.C. studio is Juliet Eilperin of The Washington Post. Welcome to all of you.

MR. GAVIN SCHMIDTThank you for having us.

LAKSHMANANAbsolutely. So let's get started, Gavin Schmidt, with some perspective. If you could explain to us how much exactly did temperatures rise last year.

SCHMIDTWell, exactly the record was broken by about .13 Celsius, about .23 Fahrenheit, but actually that doesn't really convey the magnitude of what we're seeing. We've seen a warmth of about a degree Celsius, almost two degrees Fahrenheit since the 19th century and for planetary temperatures, that's actually a very large number. If you go back to the last ice age, when we had ice sheets all over the North American continent and in Europe on a very different planet, that was only eight to nine degrees Fahrenheit colder than we are now.

SCHMIDTSo the planet notices, you know, a couple of degrees here or there, even though we might not in our daily lives.

LAKSHMANANHum. So you're saying we're only eight degrees over the ice age. But are we now one degree Celsius over preindustrial levels?

SCHMIDTSorry about the units. So eight degrees Fahrenheit above the last ice age and we are about two degrees Fahrenheit over the 19th century.

LAKSHMANANHum. All right. So was this a surprise for you and the folks at NASA?

SCHMIDTSo we've been tracking temperatures, along with our colleagues at NOAA and other (word?) groups around the world throughout the year and it was clear, I think, even in the summertime that 2015 was shaping up to be a very, very warm year. And then, in the last part of 2015, we had this large El Nino event occur in the tropical Pacific and you can see that definitely having an impact on the statistics in the last three months, particularly. And then, going into 2016, we're actually starting extremely warm yet again.

LAKSHMANANHum. All right. Well, despite the snowstorm, of course, that we've all experienced on the east coast, well, Deke Arndt, what about for you? When all the numbers were crunched, what was your reaction?

MR. DEKE ARNDTWell, just like Gavin said, we kind of saw 2015 coming as the warmest year on record, but if you consider the year kind of a 12-lap race with each month being a lap, the surge in laps 10, 11 and 12 was very, very big, surprising to me personally. I know when Jessica Blunden, my colleague here at NOAA, told me the number for December, actually, I went into my office and cried, it was so big. So the finish to the year, the last three laps of the race were really in a new neighborhood as far as the temperatures that we've seen.

LAKSHMANANSo something of a new milestone.

ARNDTVery much. So December, I believe this is the case with NASA's record as well, was the first year that was -- or the first individual month of any of the months on record that was two degrees Fahrenheit warmer than the 20th century average. That's a lot spread around the world.

LAKSHMANANAll right. Well, explain to us, Deke, how is average temperature even measured? Is it on the surface of the earth, the ocean, the atmosphere and how accurate can those measurements possibly be?

ARNDTThe global temperature, the surface temperature that we're talking about comes from weather stations on land from the different meteorological services around the world over the oceans. They are collected by ships and by buoys at sea. We combine these and NASA combines them in a slightly different way to get an overall average, what we call an anomaly or departure from a long term value. So we know what the average values are for these stations. We take the departure, the difference from that long term average, and then we combine those differences together to get a global average.

ARNDTThe fact that there are so many stations out there, there are so many ships, there are so many buoys, you know, it kind of by just the power of large numbers of observations, it really lets us hone in confidently on an estimate for the global temperature.

LAKSHMANANAll right. Well, let me ask you. You've got two years now of back-to-back record temperatures. Does that mean that the rate of climate change itself is accelerating, Deke?

ARNDTWell, the long term rate, if you consider, you know, kind of long term warming to be kind of like a ride up an escalator, so for 30 or 40 years, for several decades, we've had this long term warming effect, the escalator may be going a little faster or a little slower over time. But like Gavin mentioned, this El Nino phenomenon is like jumping up while you're on one of the steps of that escalator. So the combination of the long term ride up through long term change, plus what we call internal variability or these natural phenomena that kind of make the curve wiggle up and down, that's what you see.

ARNDTSo we had a real surge towards the end of the year. It really pushed 2015 into new territory. It's a combination of being on the tail end of three or four decades of intense warming plus an El Nino event on top of that.

LAKSHMANANHum. So the escalator brings you up and then the El Nino is like jumping up a step so you've kind of got this squiggly line going up. Is that what it looks like?

ARNDTThat's pretty much what it looks like, yes.

LAKSHMANANAll right. Well, Lisa Goddard, we've heard a lot about El Nino. What is its role in global temperature?

MS. LISA GODDARDYeah, you absolutely can see the signature of El Nino events in the global temperature. And, in fact, if you removed the trend in global temperature, what you would see is the signature of El Nino and its counterpart La Nina events. There has been some work trying to estimate the typical impact of El Nino events on globally average temperature and that comes out to be about .2 degrees Fahrenheit per two degrees -- well, I should say .1 degrees Fahrenheit per one degree of this index, SST index, of El Nino.

MS. LISA GODDARDSo as the El Nino events get bigger, the impact on global temperatures is larger. Give the magnitude of this particular El Nino event, by that formula, we would expect the impact on globally average temperatures to be about a half a degree Fahrenheit.

LAKSHMANANHum. Well, was this partly the same kind of jump that we saw with the other El Nino event that happened in '97, '98? Can you explain to us the -- is there a parallel here?

GODDARDYeah. It's quite similar. I think what's then remarkable is if we think back, that '97, '98 event, that's not even 20 years ago, how much warmer the globally average temperatures are in total this year than they were then. So we can see that signature in these particular El Nino events, but the difference between '97, '98 and this year is pretty remarkable so we can really see that change due to manmade contributions to globally average temperatures.

LAKSHMANANWell, Lisa, let me ask you that. How much of this last two years, back to back record temperatures is El Nino and how much is manmade greenhouse gas emissions? Is there a way to put a percentage on it?

GODDARDAgain, there are estimates that can be made based on the variability in the past, what similar sized events have contributed in this sort of jumping up the steps, as Deke was indicating, and again, this 2015, we would estimate on the order of half a degree Fahrenheit. But 2014 was already warm in the tropics, in the tropical Pacific. There was sort of a failed El Nino event, if you will, in 2014. So we were already starting out a big warm and then we developed this extremely large El Nino event in the last half of 2015, which really contributed to those global temperatures.

LAKSHMANANHum. So hard to put a percentage on how much is global warming, how much is El Nino. But Gavin, there's been some pushback already to last week's news, including an op-ed I saw in The Wall Street Journal yesterday by an analyst at a libertarian think tank who argued that there are flaws in the way that the government agencies measure temperatures and that all of these predictions of climate change are exaggerated. What do you say to that, Gavin?

SCHMIDTThat seems like a classic shoot the messenger strategy from people who don't actually want to see what the data is saying. You can see the global warming. It's very, very clear. You can do it in many independent data sets. Any of your listeners can go and download the raw data for themselves, make their own indices and they'll see exactly the same thing. There are always flaws in observational data and there are always flaws in the models that we use to approximate the real world. I think that's inevitable. But science works because we find a consilience of evidence.

SCHMIDTWe find lots of different independent data sets which have their own issues, but that together show what's actually going on. And we find the best explanation for all of the phenomena that we can see. It's not perfect, but the best explanation that we have for the warming over the last 30 or 40 years is the rise in greenhouse gases, predominant amongst those is carbon dioxide and that's rising because of the burning of fossil fuels, natural gas, coal, oil and deforestation.

LAKSHMANANSo if that is the predominant cause of this record warming that we've seen in the last two years, then, Deke, do you think that this news could change the view of those who are less concerned about climate change as an urgent problem or perhaps a long term, long boiling problem? You tell us, Deke.

ARNDTSure. This is a long term issue. It's going to affect the lives of our kids and the lives of their kids. This is going to be one of the issues that we continue to deal with as a species and as a country and as a culture and as a society for generations. I don't think, you know, I think like a scientist. I don't think any single piece of evidence is going to convince anybody of anything. Like Gavin said, it is a multitude of indicators that are what -- important.

ARNDTThis is how we live our lives. We place one piece of evidence against the other. So global temperature along with the ice sheets melting, along with sea level rise, along with many of the things that we see in the oceans, together they say, yes, absolutely we live in a changing world and we're going to have to deal with that.

LAKSHMANANAll right. We're going to take a short break, but stick with us. I look forward to hearing your comments and your questions. Stay tuned.

LAKSHMANANWelcome back. I'm Indira Lakshmanan sitting in for Diane Rehm. Joining me here to talk about climate change and the findings that 2015 was the hottest year on record, here in the studio, Juliet Eilperin, White House bureau chief for The Washington Post, who covered the environment and climate for The Post for nearly a decade. From the studios of WCQS in Asheville, N.C., Derek Arndt, chief of climate monitoring at NOAA. And from the studios of NPR in New York, Lisa Goddard of Columbia University and Gavin Schmidt of NASA's Goddard Institute for Space Studies. I think no relation between the two Goddards though, right?

SCHMIDTNo, I don't think so.

LAKSHMANANOkay. Well, we'll be taking your comments and your questions throughout the hour. We want to hear your thoughts about climate change, about 2015 being the hottest year on record. Call us at 1-800-433-8850. You can send us an email at drshow@wamu.org. Or you can join us on Facebook or send us a tweet. So, Juliet, you reported on climate change for almost a decade. I want to get your perspective on whether news of record warming actually changes the public's attitude. Are people's views on this fixed in stone? Or can, you know, new findings like this shift the way that the population thinks?

MS. JULIET EILPERINIt's an interesting question. What's fascinating is that the broad view of the general public has actually been fairly stable for years. We've seen that a large majority of Americans, for example, believe that climate change is happening and that there's a connection between human activity and the warming and weather changes that we've seen. And so when, whether it's The Washington Post or other news outlets have polled, that's generally been pretty stable. And certainly in recent years, as the impacts of climate change have become more evident, you have, when you follow up and ask questions, they often say they're seeing it in their real lives in a way that, for example, they didn't when I started covering the environment.

MS. JULIET EILPERINThat said, there's this sharp division both among political elites, where you've seen a real split between Democrats saying that there's this connection between human activity and climate change and the vast majority of Republican politicians saying there is not necessarily a connection or if there is it's not severe. And so -- and as well as the fact that there is a significant segment of the most conservative Republicans in the United States who don't think that this is a real issue and, when you provide them with new information, it does nothing to sway their attitudes.

LAKSHMANANHmm.

EILPERINAnd what's interesting is that segment, of course, is very important in the Republican primaries right now...

LAKSHMANANMm-hmm. Mm-hmm.

EILPERIN...in the presidential election, an so you're often seeing that view being expressed by top politicians.

LAKSHMANANHmm. All right. Well do you see this latest news -- because it is big, we've had two record hottest years back-to-back...

EILPERINRight.

LAKSHMANAN...which I understand is like a one in many thousands chance of happening...

EILPERINRight.

LAKSHMANAN...two back-to-back hottest years -- is this going to change the politics around climate policy? Do you see this now entering the Republican debate in any way?

EILPERINThe Republicans didn't issue any immediate reactions to this news. And so I think we're going to see in the days ahead to what extent they exchange in it -- engage in it. I do think what we are seeing is, for example, both Hillary Clinton and Bernie Sanders did tweet about it. You know, you had Clinton saying -- tweeting, climate change is real, it's hurting our planet and our people. We can't afford a president who ignores the science. And then the Sanders campaign also tweeted saying, climate change is real and caused by human activity. The planet and its people are in trouble.

EILPERINSo what you're seeing is the Democrats are going to make an issue of this in the presidential campaign.

LAKSHMANANMm-hmm.

EILPERINSo the Republicans are going to be forced to engage in it. And the question is, how much does it play a role in the primary or certainly in the general? Some of this news and some of these findings are absolutely going to be part of our debate over who becomes the next president.

LAKSHMANANHmm. And I'm curious about the effect on actual policymaking at the White House, with the guy who is still in power for the next year. I mean, President Obama has made slowing climate change an absolute priority for his second term. So this news, what does it mean for the climate deal in Paris that his administration pushed so hard for?

EILPERINWell, what it shows is that, you know, in the eyes of, again, President Obama and his aides and many other world leaders, that they were right to reach a climate accord in Paris and that what they put in place was what the president likes to refer to as an architecture that can raise the ambition of this agreement over time. What we've certainly seen is that if you just take at face value what countries have agreed to do now, we would miss the goal that everyone talks about of 2 degrees Celsius.

LAKSHMANANMm-hmm. Meaning keeping the climate within 2 degrees Celsius over preindustrial levels.

EILPERINOver pre -- yeah, exactly, over preindustrial level, when you're talking about a temperature rise by the end of this century. Under the commitments that were made in Paris, the temperature rise would be, in fact, 3.5 degrees Celsius, which to put it in our terms is 6.3 degrees Fahrenheit, so way over. But the idea is that, through both kind of increased targets over time and the advances of new technology, we could potentially get it down below to what people say would be a safer level.

LAKSHMANANHuh. Well, we've got an email from a listener here that sort of links to this, about the preindustrial levels, the preindustrial temperatures. A listener is asking -- and I wonder, Gavin, if you can take this one -- please ask your guests to explain how they obtained climate data for 1880. There would certainly be fewer locations measured and the technology would not have been as reliable. We're talking about changes of only a few degrees. So isn't a high degree of accuracy required?

SCHMIDTSo obviously the situation in the 19th century was less good than it is now. I mean, now we have a much deeper network and a lot more redundancy. But even in the 19th century, there was a global network of weather stations. And one of the interesting things about the way that we put these data together is that we're looking for departures from the average. So if New York is, you know, a couple of degrees warmer than average, then actually it turns out that D.C. is probably a couple of degrees warmer than average. Even though the absolute temperature might not be correlated, the departures are.

SCHMIDTAnd so the -- any individual weather station actually has a pretty large radius and influence. And we can check and we can throw out data. We can bring it in. We can split it in half. And we can make an estimate of what the averages are. So obviously it's not as good back in the 19th century as it is now. But it actually is good enough for us to know that the temperatures have warmed significantly since the 19th century.

LAKSHMANANHmm. All right. Deke, I see you nodding your head on Skype here. And I'm wondering, you know, the Northeast is still digging out of a major snowstorm from this weekend. There were heat waves in Europe and Russia that have killed tens of thousands of people since 2003. There were thousands of people who died in India last year from their second-worst heat wave on record. So to what extent can we attribute extreme weather events to this gradual temperature rise and climate change in general?

MR. DEREK ARNDTYeah. Connecting a single big event to long-term climate change is a pretty arduous task. It's not impossible, but it's challenging. And it's played out kind of on the timescales of science. So the instant connection is kind of a fallacy. But what we can look at are the kind of aggregate of these types of events in places where we have robust historical data. And what we see is a pattern, that these events kind of fit a pattern. We're seeing more and more big heat events, you know, the duration of these events, the intensity of these events...

LAKSHMANANMm-hmm.

ARNDT...the frequency of these events. We're seeing more big rain events. So a lot of rain in single doses. Statistically, we're seeing that play out throughout, you know, the country -- especially east of the Mississippi and in other places around the world where we have a robust record. We are seeing a decrease in big cold events, although they still happen. We still occasionally break records for cold days and cold months. But we don’t break them nearly as often, or threaten them nearly as often as we do on the warm side. So these events, they fit a pattern.

ARNDTThere is an emerging and very exciting field of climate science where scientists are looking at the attribution, you know, what are the chances that this particular event was influenced by climate change or had the chance of it happening affected by climate change? And we're going to see that science really evolve over the next few years and give us a lot more answers for individual events.

LAKSHMANANHmm.

ARNDTBut for the big picture, the picture's pretty clear.

LAKSHMANANSo it sounds like you're saying this is like a new frontier in climate science. Will we ever be able to attribute specific events, like this storm or that drought, to climate change?

ARNDTSo, you know, we can -- the climate and any weather -- even a single, big weather event is a complex thing and it has many factors. And a great example is the Hurricane Sandy that impacted New York and New Jersey and the Northeast.

LAKSHMANANMm-hmm.

ARNDTYou know, the dynamics of Sandy as a storm and the path of Sandy as a storm, we can study that and begin to make connections to climate change -- or not make connections. But one thing's undeniable, the sea level has risen by several inches since the middle 20th century. And so Sandy was pushing a lot more water into, you know, our largest city. That is a result of climate change. So the consequences of some events are fueled by climate change or informed by climate change, just as much as the dynamics that went in to the big event.

LAKSHMANANHmm. Well we have another listener email here that I think would be good for Lisa. Cliff, in Texas, is asking, was the stronger El Nino this year also due to global warming? So is this part of this spiraling upwards that you talked about?

GODDARDThere is a lot of research going on in that area. And I believe that it's really too early to make any sort of conclusions on how climate change itself is influencing any particular El Nino event and even the sort of the last 10 or 20 years of El Nino events that we've had. We know that we've had events of this magnitude back in the 19th century. We also know that there are periods -- decades-long periods -- when you have very quiet Tropical Pacific, very few El Nino events, and then you have decades where you have very active, large El Nino events. And so I would say that the bulk of the evidence right now suggests that it's just part of the natural event-to-event variability of El Nino phenomenon.

LAKSHMANANAnd that this also is part of looking at weather patterns with regard to climate change in the shorter term?

GODDARDSo if I understand your question, it's that El Nino helps us understand the regional climate that we might expect over the next, say, months to a year.

LAKSHMANANMm-hmm.

GODDARDAnd in that case, absolutely. El Nino gives us a lot of information on expectations of regional climate. Some of those things are going to be impacted or made worse by climate change. But we've had variability in the climate forever. And the variability in the climate's going to continue. But as temperatures get warmer, these things that you mentioned before -- the heat waves and the droughts -- will just be made worse. And they will appear more frequent, because you'll cross those adverse thresholds more often on a warmer baseline.

LAKSHMANANI'm Indira Lakshmanan and you're listing to "The Diane Rehm Show." If you'd like to join us, you can give us a call at 1-800-433-8850. You can send us an email to drshow@wamu.org. Or follow us on Facebook and send us a tweet. So, Deke, what else do we know about shorter-term weather trends related to climate change that affect us? I'm thinking not only -- I'm thinking about the whole picture: El Nino, ocean patterns, something I read about called Pacific Decadal Oscillation, you can explain that to us. But tell us what else about short-term weather trends are related to climate change.

ARNDTWell the Pacific Decadal Oscillation -- and I promise we won't use that term again...

LAKSHMANANThank you.

ARNDT...that's part of a big family of what we, you know, what Dr. Goddard referred to as climate variabilities. So these are kind of natural oscillations or patterns or swings or however you want to think about them, that occur in a climate system that, for lack of a better description, they kind of move energy in the different parts of the ocean or the atmosphere. And certain outcomes, seasonal outcomes or decadal outcomes are kind of preferred during these regimes. The El Nino and that oscillation we mentioned earlier are kind of loosely connected in a family.

ARNDTAnd these things can kind of affect our seasonal outcomes. They tilt the odds towards a wetter winter or a drier winter or warmer or colder winter, you know, kind of depending on where you are and how strong the event is. You know, these things have been going on independently of climate change for as long as we know. So the good question is, how will climate change kind of change them as they go? Will they change them? Will they affect them? You know, but we will continue to deal with these seasonal and regional phenomena that have shaped our weather outcomes over time.

ARNDTThe place where climate change comes in really is, you know, are they affecting the kind of performance, for lack of a better term, of these phenomena? Or are they bringing new consequences such as higher sea levels or a more moister and energetic atmosphere into play, that may kind of be a game changer in outcomes? And that's an active area of research.

LAKSHMANANWell, Gavin, can you connect this to the actual headlines for us? Last year, we heard about the heat waves in India and Pakistan and in Russia. I mean, is part of this about extreme weather events last year happening because the systems that we're familiar with stayed in place longer than usual?

SCHMIDTSo, there's a lot of subtlety to discussing extreme events. I mean the first thing to realize, of course, is that extreme events covers a whole range of very, very different phenomena. And you really can't lump them all together. As Deke mentioned, you know, we are seeing a greater number of heat waves. We're seeing less cold-air outbreaks. All right? So there, the bell curve, if you like is shifting.

SCHMIDTOne of the things that I think Deke also kind of alluded to -- and there was a couple of good examples of this last year -- was that, for instance, rainfall and drought changes. In California, people have looked at whether there was a climate-change signal to the rainfall that they didn't get. And that's actually very hard to find. But the impacts of the drought were worse because the temperatures were warmer. And so the temperatures -- there is a climate-change signal. And so the impact of a drought -- even if the drought itself had been initiated in a totally natural manner, if you like -- the impacts were worse.

SCHMIDTAnd the same thing with the example of Sandy. The storm surge -- not just from Sandy but from any large storm -- those impacts are increasing, whether it's in Miami or Newport Beach or on the Jersey Shore, the impacts of those storms are increasing because of higher sea level, which is due to more heat going into the ocean -- the ocean expands -- and more ice around the world melting also raising sea level.

LAKSHMANANHmm.

SCHMIDTAnd those are attributable to climate change. And so you can distinguish, I think, perhaps between changes in the dynamics, which are very hard to see because of the complexity, and change in the impacts of extreme weather, which actually are becoming more manifest. Because that -- we're living on a different baseline. The baseline for climate has shifted over the last century and will continue to shift.

LAKSHMANANAll right. Well, Lisa, what are the tools that scientists need in order to make better predictions about weather patterns related to climate change?

GODDARDThe main tool that we use for predictions are these dynamical models. They're models of the physics and the thermodynamics of the climate system -- the oceans and the atmosphere -- and even their interaction with land and ice. And we try to represent those processes, how greenhouse gases are influencing them, how an El Nino event might play out in our global climate. So those are the types of tools that we primarily use. As was mentioned very early on in this program, the models are not perfect and we know that. But we have a good sense of what they do right and what they do less right. And we can take advantage of the information that they can provide.

GODDARDDuring El Nino events is really when we have the most predictability of our seasonal climate. And this is a learning opportunity for how to be better prepared for the climate. And that preparedness incrementally helps us be better prepared for the longer-term future.

LAKSHMANANAll right. We're going to take a short break now. And when we're back, we're going to go to your calls and your questions. Stay with us.

LAKSHMANANWelcome back. I'm Indira Lakshmanan, sitting in for Diane Rehm. We are discussing climate change and 2015 as the hottest year on record. With climate scientists Lisa Goddard, Gavin Schmidt, Derek Arndt and Juliet Eilperin of the Washington Post. We're going to go to the phones now. I'd like to take the first question from Michael in Alexandria. Michael, you're on the air.

MICHAELHello.

LAKSHMANANHi.

MICHAELMy question is for all the media in general.

LAKSHMANANOkay.

MICHAELAnd journalists who work for the media, including NPR. Every time I hear on radio or on TV, a Republican office holder or candidate being interviewed, they're not confronted with the question of why the entire Republican Party continues to deny the reality of climate change. And if they do admit the reality of climate change, why aren't they asked what they plan to do about it?

LAKSHMANANOkay.

MICHAELBecause I know that nothing is going to get done with a Republican controlled Congress and the media needs to start pushing and directly asking Republicans, office holders and candidates for office, why they continue to deny this issue, why they continue to behave in a grossly and criminally negligent manner about this serious crisis.

LAKSHMANANOkay. Michael from Alexandria wants to know about the gross negligent crisis and why journalists are not doing their job, so Juliet, you're the one journalist at the table.

EILPERINExactly.

LAKSHMANANI think we need to put it to you.

EILPERINI will represent all the media. I'm actually going to start with NPR and say that if you listen closely to, for example, Steve Inskeep extensively questioned Ted Cruz about this topic within the last couple months. So, there was certainly a "Morning Edition" segment where he went back and forth, more than once, with the Texas Senator on it. So I think there are occasions where it's brought up. I think Michael makes an excellent point and I wanted to add a couple data points to that.

EILPERINIn terms of the Republican -- I think, certainly, it's being raised less frequently right now. As I mentioned, I definitely think it's going to be a serious topic in the general election. In the primary, it's true that when you, for example, look at the Presidential debates, it's come up on the Democratic side because again, they're always trying to figure out where they are positioned vis-a-vis each other, I don't recall a question -- and I've watched most of the Republican debates -- where this has come up on, you know, in terms of all those Republican candidates. And so I certainly think it's a question to ask the networks, why they haven't been raising it.

EILPERINBut one kind of context I wanted to provide for this, and I think that this is a classic issue that comes up when we do reporting on presidential campaigns, which is that you often have reporters who are specialized in political coverage who have not covered issue areas as much.

LAKSHMANANMm-hmm.

EILPERINAnd so one thing that's very interesting is that during 2008, while I was full time covering the environment, the editors at The Post decided I wasn't busy enough and they put me on the McCain campaign. I actually did multiple Republican candidates. And then I covered Senator McCain and Sarah Palin -- Governor Palin at the time. And what was interesting is, at that point, you had both candidates who said climate change was a problem and wanted mandatory national curbs on greenhouse gas emissions...

LAKSHMANANMm-hmm.

EILPERIN...including Senator McCain. And at one point, I asked him, on the Straight Talk Express, we talked about the policy...

LAKSHMANANHis campaign trail?

EILPERINHis campaign bus.

LAKSHMANANBus.

EILPERINAnd it's either that or the plane -- it might have been the plan. But basically I raised this. And I started talking about the difference between him and Obama and what he wanted to do. And he turned to me and said, well, I defer to you. And everyone started laughing. Because, of course, Senator McCain knew that I had covered this material. And I told him I wasn't his spokesperson and he'd have to give me an answer on policy. But it showed you that I had a familiarity with this. So I could talk in detail in a way that really none of my colleagues on the campaign at that point could.

LAKSHMANANSo a lot of the journalists aren't familiar with the issues. And maybe the candidates themselves, the politicians themselves aren't exactly familiar with the issue either, it sounds like, from your anecdote.

EILPERINRight.

LAKSHMANANAll right. Well, we've got an email from Ken, that says -- I think this has to go to one of our climate scientists. Maybe Deke would like to take it. He says, where exactly was it warmer last year? Here, in Michigan, for example, we had below normal temperatures for all of 2015, making your claims kind of unbelievable to me. Deke.

ARNDTWell, every state in the Union had above-normal temperatures during 2015.

LAKSHMANANSo that includes Michigan.

ARNDTYeah. The upper Midwest did start out very cold. It had a pretty severe start to the year and a very, very warm finish to the year. 2015, globally speaking, it was really driven largely by the oceans. The Tropical Pacific, as you would expect in an El Nino event, was very warm. And the Indian Ocean, in particular was very, very warm. But, you know, it was plain. It was everywhere. You know, this wasn't just El Nino pushing the needle just past the limit. The planet is warm Every major ocean basin and every major continent had areas -- significant areas that were record warm or near-record warm.

ARNDTYou put that together like a big mosaic and what you get is a year that pretty much kept all of the other years in the modern historical record at arm's length. It was a big year. It was certainly helped out by the El Nino phenomenon but it was a global -- it was global warmth.

LAKSHMANANOkay. I have an email here from Alex, who wants to ask Lisa about which of the world's most vulnerable populations she's most concerned about in light of the news of the accelerated warming.

GODDARDI'm really concerned about all of them. And including -- it's not just the developing countries that are vulnerable. Even the places like the United States has a lot of vulnerable populations. So as the climate gets warmer and these heat waves or droughts become exacerbated, that's a big concern. What the developing countries lack in many cases is adequate historical data or even monitoring of what's going on right now. And so what happens then is that there is more response to disasters where there could be better preparedness.

GODDARDAnd so I think that one of the investments in effort and resources that could really help these vulnerable populations is to improve the observations and the access to that information, which can then go into better forecasts, better preparedness and better decisions ahead of disasters.

LAKSHMANANMm-hmm. Okay. Juliet, you wanted to jump in on that.

EILPERINYeah. You know, what I think is interesting about that question is it raises the -- we talk about these abstract things, 2 degrees Celsius, 1.5 degrees Celsius. But, you know, there are some groups who have put this in context in terms of its real-world impact. And the research organization Climate Central, which does research as well as some advocacy, recently said that 280 million people live on land that could eventually be submerged underwater, if, for example, we reach 2 degrees Celsius.

EILPERINBut if, for example, the world met this lower target they talked about in Paris of 1.5 degrees C, it would be cut by more than half to 137 million people. So that's a huge difference in the number of people who would essentially lose the place that they're living and become refugees.

LAKSHMANANMm-hmm.

EILPERINAnd so that's one of the ways to think about...

LAKSHMANANSo we're not just talking about Bangladesh. We're not just talking about low-lying places like the Maldives. We're talking about a much greater proportion of the Earth, you're saying.

EILPERINAbsolutely.

LAKSHMANANGavin, I want to ask you, you know, all of this talk about 2 degrees Celsius, to non-scientists like ourselves, or myself at least...

SCHMIDTRight.

LAKSHMANAN...a lot of this is very kind of, it sounds very abstract. Try to put it in layman's terms for us, what you just told us about temperature rising two years back-to-back, record highs. What does this mean for the Paris accord? They set a target of not going up more than 2 degrees Celsius over preindustrial levels. But now, this is the first year where we're clearly 1 degree Celsius above the 19th century already, right? So what does this mean for the Paris accord? Do we just rip it up and go home and start all over again?

SCHMIDTI think you have to think about the 2 degree -- I don't like talking about it as a target, as if we were aiming for it -- more of a guiderail. One should think about it like a speed limit going around a corner. You know, is anything really dramatically different if you go around a corner at 45 or at 46? No. But as you speed up, damages, impacts, risk increases. And so as the global temperature increases, damages, risks and impacts are going to increase. In fact, we're already seeing that now. And that's only going to continue as we go forward. So 2 degrees or even the 1.5 degrees is an aspiration. Whether we're going to get there depends very much on what societies decide to do about it.

SCHMIDTAnd while people, you know, who signed up to the Paris accord or groups who signed up for that, are making pledges that go some direction towards meeting that goal, they're not really commensurate with the size of the problem. And so let's put that into perspective. Carbon dioxide emissions are continuing to increase. We've just passed 400 parts per million in the atmosphere. We're not going to see a lower level than that ever again. And every year it goes up by about 2.5 to 3 parts per million again. To get that just to be stable, we have to cut emissions globally by about 60 to 70 percent. And for it to stay stable and to actually go down, we'd have to cut emissions by about 80 percent.

SCHMIDTAnd then by the end of the century, you'd have to have negative emissions. You'd have to be drawing carbon dioxide out of the atmosphere artificially.

LAKSHMANANHmm.

SCHMIDTSo growing artificial trees or something. And that's, you know, the technology is in a very theoretical state….

LAKSHMANANIt's not there yet.

SCHMIDT...when it comes to doing it. Well, I mean, it's there in theory. But, in practice, making that work is a very large ask.

LAKSHMANANThat sounds like a really big hill to climb you're talking about.

SCHMIDTYeah. So I'm in a bit of a quandary. You know, I'm a physical scientist. You know, the 2 degrees number is very much a political target. It's a negotiation. I think, if you asked a climate scientist, how much warmer do you want the planet to get? The answer would be not at all. And, you know, you'd want it actually to cool down a little bit because right now we're still seeing...

LAKSHMANANMm-hmm.

SCHMIDT...unstable ice sheets, we're still seeing sea level rise. To bring that down, you'd actually want to cool the climate. And there's no real possibility of that happening short of...

LAKSHMANANFor artificially cooling the planet.

SCHMIDT...short of doing it artificially. And then that's a whole 'nother can of worms.

LAKSHMANANWow. Okay. I'd like to go to the phones. Let's take this call from Jerry in Paducah, Ky. Jerry, you're on the air.

JERRYThank you so much. I've heard two statements being made. The first one is that if we don't reverse global warming in the next eight to ten years, it's going to be irreversible. And the other statement, number two, is that within the next 10 to 20 years, the world is going to more than double its need of energy.

LAKSHMANANHmm.

JERRYIt seems to me that those two statements are not joint possibilities.

LAKSHMANANMm-hmm.

JERRYWould your panel please comment on those.

LAKSHMANANAll right. Well, two things working in cross purposes. Thank you so much for that great question, Jerry. Deke, can you address that?

ARNDTSure. So, you know, as far as...

LAKSHMANANGrowing need for energy plus need to cool the climate.

ARNDTSure. You know, we're living in a world where many parts of the world are becoming wealthier and are increasing their appetite for energy. The kind of historical track to that is the burning of fossil fuels. And so that seems like a pathway to go down. And that will continue to warm the planet. Those emissions will basically amplify the warming signal that we've seen. As far as going back -- the irreversibility, so to speak, of climate change -- you know, I don't think in our lifetime we are going to see an early-20th century climate in total around the world again.

LAKSHMANANHmm.

ARNDTWe have committed to significant changes. And so while there is some discussion of putting Humpty-Dumpty back together again, in many ways the adaptation path, you know, the dealing with the changes that we've already committed to -- whether we have some kind of breakthrough that helps us begin to restore the climate or not -- are going to be really important.

ARNDTYou know, we are actively evacuating our American brothers and sisters from coastal communities, Native-American communities, Native-Alaskan communities. Now that's a consequence right now, as the ground literally thaws beneath their feet, it is more susceptible to wave action and it is eroding away the ground that they've built their infrastructure on, that they've buried their ancestors in. You know, we are dealing with that right now. So these are the types of consequences that we are going to have to adapt to. We're going to have to think ahead. We're going to have to work...

LAKSHMANANOkay.

ARNDT...with institutions that think ahead.

LAKSHMANANAll right. I'm Indira Lakshmanan and you're listening to "The Diane Rehm Show." Juliet, we've gotten an email here from Earl in Newfane, Vt., who says, the problem with a majority of people, quote, "believing the science," is that it is not an immediate threat to people's lives, as might be terrorism or the economy. Extreme weather events always seem to happen somewhere else. I guess, unless you lived through Hurricane Sandy, for example. But they're not really affecting everyone simultaneously. It's very easy for people to forget about the effects of climate change when it's not currently impacting them.

EILPERINThat's a very astute observation. And the listener is really touching on this point, which is that, even when I quote you these statistics about how, you know, say, two-thirds of Americans think that climate change is happening and that humans are contributing to it, when you look at where the environment and climate change ranks on the order of voters' priorities, it is always on the bottom of the list. And that is...

LAKSHMANANHmm.

EILPERIN...what -- President Obama would agree with it.

LAKSHMANANHmm.

EILPERINIf you, you know, he's said as much. And so...

LAKSHMANANMeaning that people need to feel more urgent about it. But it isn't urgent because it just seems to be too slow moving.

EILPERINRight. And so just depending on -- and the fact is we'll see whether that changes, you know, again, both with some of these impacts and with the idea that leading presidential candidates are going to talk about it more. But it is true that lawmakers generally only respond to priorities that voters make clear are urgent, are something that's going to determine what they're going to do when they enter the voting booth.

LAKSHMANANHmm. All right. I wonder whether we should be turning more attention away from stopping climate change -- or not necessarily away, but towards adapting to it? I mean that's a question that we hear more and more. Some listeners have written in about that. You know, once climate change is happening and in an inexorable path, how do we adapt to it? Deke.

ARNDTWell, you know, some obvious answers are hardening of infrastructure. There's going to be a big public health challenge, because of warmer summers in particular, you know, are challenging to people that work outdoors, particularly day laborers that work early in the morning. You know, so public health, infrastructure, and agriculture and horticulture. Understanding that the crops that we rely on are going to need to migrate themselves in a changing world. And, you know, so those are just a few -- and energy consumption. You know, the South is going to get warmer and need more cooling. And the North is going to warm and maybe need less heating over time. So these are the types of kind of big picture adaptation events.

ARNDTOf course there's all kinds of local detail buried within those. But adaptation, you know, is certainly something we need to do to be climate smart.

LAKSHMANANAll right. Let's take a call from David in Hedgesville, W.V. David, you're on the air.

DAVIDGood morning.

LAKSHMANANGood morning.

DAVIDI have a comment and an admonition. The comment is, I was really disappointed that the Paris accords didn't mention population. Because our problem is not a billion people putting carbon in the air, it's 7 billion doing it.

LAKSHMANANMm-hmm.

DAVIDAnd my admonition is to scientists in general, not your panel, that they need to do a better job of explaining greenhouse -- how the greenhouse gases warm the planet.

LAKSHMANANMm-hmm.

DAVIDYou know, people, they still cannot visualize carbon dioxide, covalent bonds vibrating and holding the energy. But they might feel that -- visualize tadpoles swimming downstream through a sieve, turning into frogs and not being able to get back out again. So if they could dumb-down the science a little bit maybe we could get a consensus to try to do something.

LAKSHMANANAll right. Thank you, David. So he's saying people won't be inspired to change things that they don't understand. Gavin, tell us a little bit about that. What responsibility is on your shoulders? And with the one minute we have left, is 2016 going to be even hotter than this last year?

SCHMIDTSo 2016 is very likely to be hotter than this year because we're starting off with an El Nino and that's historically been a trigger for an exceptionally warm year ahead. As to the communication challenge, you know, I share your caller's desire for, you know, easy to understand explanations of what's going on. And we try very hard at NASA to make accessible both the raw data, explanations of that data, and my colleagues at IRI do the same thing. NASA.gov, IRI.columbia.edu, these are the places to go for trusted -- trustable information.

LAKSHMANANTo learn even more. Thank you so much for...