MS. DIANE REHMThanks for joining us. I'm Diane Rehm. Two years ago, the Pew Center found a stark partisan divide in attitudes toward climate change. Democrats were much more likely than Republicans to agree there is solid evidence the earth is warming. But as the nation faces drought and record heat, a stronger consensus is growing.

MS. DIANE REHMJoining me in the studio to talk about the science and politics of climate change: Michael MacCracken of the Climate Institute and Juliet Eilperin of The Washington Post. Joining us from a studio in Berkeley is Richard Muller of the University of California. And throughout the hour, I'll look forward to hearing your questions and comments. Join us by phone at 800-433-8850. Send us you email to drshow@wamu.org. Follow us on Facebook or Twitter. Good morning to all of you.

PROF. RICHARD MULLERGood morning.

MS. JULIET EILPERINGood morning.

MR. MICHAEL MACCRACKENGood morning.

REHMGood to have you all with us. Richard Muller, you have, until recently, called yourself a climate change skeptic, but now you've written about your conversion. Tell us what brought that about and what you mean.

MULLERIf you'd asked me three years ago whether I thought there was global warming or climate change, I would have said, I don't know. I'm an agnostic. The reason is that there were thoughtful skeptics who raised issues that, in my mind, were valid. The -- there's a lot of anecdotal evidence about hurricanes and tornadoes and so on. And when I looked at that carefully, I decided that that was not valid. Hurricanes are not increasing. Hurricane Katrina is not due to global warming and so on. We can go to that in detail.

MULLERThe key evidence was the temperature rise, and there were some complaints. Remarkably, I talked to both Democrats and Republicans, and the Republicans seemed to be aware of these issues. The temperature stations, these official stations used to record the temperature, had terrible quality on average. The analysis had been done by choosing from 7 percent to 20 percent of the stations and, you know, some serious worry that that was done in a biased way. There were other issues, too.

MULLERSo I couldn't get a good -- an answer that would convince me. And the answer was then to put together a scientific team, about a dozen scientists, who worked at this for three years. Nine months ago, we concluded that global warming was real. The temperature had gone up about what the government had said, the IPCC, the international agency that forms the consensus on this. So that was a big step. And then we began looking deeper into it.

MULLERThanks largely, I think, to the great work of my lead young scientist, Robert Rohde, we were able to extend the record back to 1753. That's astonishing to me, that we could do that, and we could talk about how it was we could do that. But once we went back that far, we can now search for the signatures of different causes. So we could clearly see the volcanic effect, but it was short lived. We look for the solar variability, the changing sun. And to my astonishment -- this was just a few months ago -- it wasn't there.

MULLERThis was the major alternative theory for why the temperature had gone up. Finally, I tried many other things, just mathematical functions, plot of the population. When I tried carbon dioxide, it was right on.

REHMInteresting.

MULLERIt was a match to the signature. And at that point, it was my aha moment. Yes, it is carbon dioxide. And more remarkably, the fact that we can rule out the volcanoes and the solar variability and get such a good fit simply from the carbon dioxide now suggests that it's not just most of the warming, which is what the official report says, but that essentially all of the warming since the 1700s came from human-caused carbon dioxide.

REHMRichard Muller, he's professor of physics at the University of California, Berkeley. He is author of the book titled "Energy for Future Presidents: The Science Behind the Headlines." And now turning to you, Michael MacCracken, are you irritated? Are you angered by the lack of support from some scientists out there who've been so slow to reach the conclusion that global warming is at least partly human-induced?

MACCRACKENWell, I think we're pleased that one of the prominent ones who was doubtful decided to basically kick the tires and see what they found out, basically went after one of the aspects that is sometimes considered, you know, had more questions about it. He went after it, and he found it was solid. And, I guess, I would argue that lots of the other parts are done as well and extensively, and they're solid as well.

MACCRACKENSo what we really have had for quite a long time, several decades at least, is a real sense in the scientific community that human activities are changing the climate, that it's happening now and exhibited in some places, the Arctic being one primary example, but also in precipitation systems. So we're (unintelligible). We're glad to have him join. We hope the others, you know, will keep looking and will come over and understand the science.

MACCRACKENIt's unfortunate that it's sort of delaying doing something about it because it is just absolutely urgent to get started to limit emissions and limit climate change.

REHMMichael MacCracken, he's chief scientist at the Climate Institute and lead editor for the book "The Sudden and Disruptive Climate Change: Exploring the Real Risks and How We Can Avoid Them." Juliet Eilperin, is there now a growing consensus about climate change?

EILPERINWell, interestingly, in terms of public opinion, it's been fairly consistent for a while. You've had roughly three-quarters of the American public who have said that human activity plays at least part of a role in causing warming that we've seen in recent decades. And so, for example, The Washington Post did a poll this summer that found that, and so that number has not changed dramatically.

EILPERINAnd then also, while there's definitely a division -- more Democrats and independents believe this -- there is certainly -- for example, 62 percent of Republicans in our poll thought that either human activity is partly or entirely to blame for climate change that we've seen in the past century.

REHMI gather the change you've seen in public opinion has more to do with how urgent a problem people see it.

EILPERINAbsolutely. So what's interesting, what we've seen is we've seen a decline in the sense of urgency. And so, for example, in our poll, only 18 percent of respondents identified this as the top environmental problem we're facing...

REHMCompared to?

EILPERIN...compared to 33 percent in 2007 when there was a great deal of publicity around the IPCC report that Dr. Muller referred to. And so I think, you know, what's interesting is that you certainly do see, you know, with this announcement, there, you know -- and I've noticed, for example, a shift in some of the, for example, self-identified skeptics I talked to that often they are now saying, we don't question that human activity is contributing to climate change.

EILPERINThe question is how much or how significant a problem this will be in the future. And so you are seeing somewhat of a shift. There, even as, for example, you see among the Republican leadership that there is more of a willingness across the board to question the science even as you see certain, you know, scientists testing this out and coming to the conclusion that human activity plays a major role.

REHMJuliet Eilperin, she's national environmental reporter for The Washington Post. She's author of the book "Demon Fish: Travels Through the Hidden World of Sharks." We are going to take your calls, 800-433-8850. Coming back to you, Richard Muller, Michael MacCracken mentioned the delay that the skeptics have brought about by virtue of non-believing, and therefore, perhaps the U.S. has not taken the kind of action it should've as quickly as it should've. How do you respond?

MULLERWell, in my mind, it wasn't completely bare. I think that the actions that have been proposed, for the most part, when I look at it, the numbers will not do the job. People somehow ignored the fact that the global warming that's predicted is predicted to be bad, and I'm concerned about that. And I think we need to do something about it, but that most of it is going to be coming from the developing world, primarily China which, by the end of this year, will be producing twice the level of the U.S.

MULLERAnd so with this rush to action, there's been a lot of misdirection. If, for example, we, in the U.S., begin to build electric automobiles because it will set an example, an electric automobile in China emits more carbon dioxide than the gasoline one precisely because it gets its energy from coal. So, although a lot of people have had a call to action, the action has not been, in my mind, an action that would really work.

MULLERIf we want to do something, it has to be something that China can afford to follow, that it will follow, that will make sense. Anything we do in the U.S., the U.S.'s contribution in the future is not going to be that big.

REHMJuliet.

EILPERINI've covered in the national climate negotiations for several years at this point. And what you see repeatedly is that when you look at the leaders of the developing world, in China and India, who, frankly, have taken on a suite of activities aimed at curbing their carbon footprint. Although, there's absolutely no question, when you look at the numbers, the developing world is the driver of carbon dioxide emissions worldwide at this point.

EILPERINThey consistently point to the U.S. and the fact that we have not adopted finding limits on greenhouse gasses. And so, while I think that this is a very good point, you have to look at the interconnection between these policies.

REHMJuliet Eilperin of The Washington Post, Richard Muller of the University of California at Berkley and Michael MacCracken of the Climate Institute. Your calls, emails when we come back.

REHMAnd welcome back. We are talking about the ongoing debate over climate change, yet there are more and more individuals in the scientific world who are acknowledging not only that the climate is warming, but that that warming process is in part man-made. Richard Muller is one of those who called himself a skeptic. He has now written an extensive piece for The New York Times. That piece came out July 28. It's titled "The Conversion of a Climate-Change Skeptic." He's on the line with us from Berkeley, Calif.

REHMJuliet Eilperin is here in the studio. She is the environmental reporter for The Washington Post. And Michael MacCracken, he is chief scientist at the Climate Institute. Michael, just before the break, I asked both Richard Muller and Juliet about the question on delay and whether more could've been done more quickly.

MACCRACKENWell, I think it's important to realize in thinking about the developed and developing world that even if the developing world had zero emissions tomorrow and went on, we would have a problem from the emissions in the developed world going on. We would keep rising. It's partly because we've had most of the emissions in the past, and we're continuing to put out emissions.

MACCRACKENConversely, even if the developing -- developed world went to zero and the developing world continues on their track, they'd have a problem. So we're both in this together, and we really both have to work aggressively to do it. Now, Prof. Muller is right. We got to find a strategy that can work for both sides, and I think there is one that one sort of points to. For the developed world, we have to get our emissions under control, and we have to demonstrate that a modern economy can prosper on low CO2 emissions. So we have to make some changes and do that and...

REHMDo electric cars make sense?

MACCRACKENWell, it depends where you are in the development stage. I mean, in the U.S., you can do a lot about supply of electricity to go renewable and get away from coal and get away from natural gas as well -- we're going to have to do. But there's a lot you can do in that regard.

MACCRACKENI guess what I wanted to say, though, is, while the developed countries are working so hard on CO2 and really demonstrating it, and you want China to be as conservative and efficient as they can, the other major contribution to near-term climate change is short-lived species that comes from methane and black carbon and tropospheric ozone. In a major U.N. assessment on last year -- published last year, basically made clear that if you want to have an effect before 2050, you really have to go hard after these species, and we can do that.

MACCRACKENThe U.S. has had voluntary programs established by President Bush. They need to be mandatory and implemented more strongly. They're not very costly to do. And China and India will want to do them because they improve air pollution. They improve public health. They improve energy efficiency. And so get them working on the part of the problem where they can make a real difference. So there's ways to an international agreement.

MACCRACKENSecretary Clinton, last February, announced an effort in this regard. I don't think it's big enough, but it's a start. And so I think there is a way to really do it, but we have to work aggressively.

REHMAll right. And before we go any further with this, Juliet, I'd like to understand some of the politics that have gone on. As we've all said, Republicans have been far more skeptical, Democrats have been far more in favor, understanding, they believe, that the planet was warming, we had to do something. Why has there been such an effort on behalf of some very conservative groups and individuals, like the Koch brothers, against the idea that the planet was warming?

EILPERINWell, really what you're seeing is a combination of ideology and economics. I think that there are a couple of things. You know, for example, one thing when you look at Europe, which has been far more aggressive in terms of adopting policies to curb greenhouse gases, they have a tradition of the idea that society sometimes does things collectively for the good of the whole that might involve a certain degree of sacrifice of higher taxes and things like that.

EILPERINCertainly, the American culture is not as set up to embrace that kind of action, that there is a culture of individualism, which certainly is prized by many Americans, including many Republicans. And there is an idea that why should, you know, we should drive any car that we want, we should have any size house and things like that, and we shouldn't have as much of a concern about the environmental impact.

EILPERINThen clearly there are financial interests who are invested in, for example, the continuation of fossil fuel extraction, and we've seen this. And they've been very straightforward, whether you're talking about the oil industry or the coil -- coal industry, and they have been very resistant to the idea of changing over and making a transition to renewable energy at the cost of higher energy.

EILPERINAnd so you've seen those two things coupled with the growing influence of the Tea Party, where you certainly have a number of people who, again, are just inclined not to be as invested in this idea that climate change poses a threat, and they are holding their leader's feet to the fire and saying, you're not going to win the presidential nomination, you're not going to win nomination at a congressional district if you raise questions and argue that we should curb greenhouse gas emissions.

REHMSo this has very much become a political issue as well as a scientific one. Michael.

MACCRACKENYeah. But I'd like to sort of try and divide it a little differently between conservative and liberal. Scientists don't like to be wrong, and so what we do is we say there's a relatively large range of possibilities looking ahead 100 years. There's changes about what our emission strategy will be and climate.

REHMSure.

MACCRACKENFossil fuel advocates will say, all the scientists are sure of is the lower bound, so they will take that. Environmentalists will say, we only have one Earth. We better be very careful. You scientists say it could be as much as this. There are other groups. Some of the religious groups have come in, and they're interested in issues of stewardship and equity. What about the rich versus the poor, this generation versus future generations?

MACCRACKENThere's a really wide range of views. They've gotten consolidated somehow in this political way that sort of groups of them in certain ways. But there's really a wider set of perspectives to consider.

REHMRichard Muller.

MULLERThe idea that we should emulate Europe, I think, is mistaken. In the last five years, the emissions from Europe have increased, while in the United States they've gone down. At the same time in China, last year, a recent report put out by the Chinese themselves says that their coal use has gone up 9.7 percent. This is -- if the U.S. were to cut to zero within four years, the Chinese growth alone would make up for that.

MULLERI think what's missing here is a place where perhaps I disagree with Michael. He says we must avoid natural gas. In fact, the reason the United States' emissions have been going down is because we're switching from coal to natural gas. The problem in China, as I see it, the only thing they can afford to do -- they have to be profitable. If it's not profitable in China, it's not sustainable.

MULLERThere are two actions that we can take. One of them would be to help them with enormous conservation and energy efficiency efforts. This is very important. There's a lot to be gained and it's profitable. But the other thing we have to do is switch their economy from coal -- 70 percent or more than 70 percent of their energy comes from coal, which emits three times the greenhouse emissions of natural gas.

MULLERWe've got to switch them from coal to natural gas. It's the most important thing we can do. And I'm sad that so many of my environmentalist friends have decided, I think, prematurely to oppose natural gas because it is a fossil fuel. It, in fact, has one-third the emissions, and it is why we are reducing our emissions when Europe isn't, and it's the most important thing other than energy conservation that can be done in China.

REHMAnd let's talk about the fracking that's going on in this country and the result of natural gas, Michael MacCracken.

MACCRACKENWell, I guess the first thing is we certainly agree that efficiency is the first thing to do. I mean, for the U.S., there have been National Academy and other studies that have said U.S. could reduce its emissions by 30 percent or something with cost-effective technologies that exist today. So that's certainly the very first thing to do. What I was saying for the U.S. is that if what we do is a major switch to natural gas, we're going to have to make another transition in the following couple of decades away from natural gas if we're going to slow climate change.

MACCRACKENSo for us, we need to think about, it seems to me, working very hard on other things, the renewables, and use the natural gas to fill in on the intermittency, use a better grid and other things. But put -- I mean, certainly do natural gas if you have to, but don't think about that as the long-term solution.

REHMJuliet, do you want to comment?

EILPERINYeah. I was just going to comment on in terms of this switch over to natural gas, which, of course, Dr. Muller is right that that's largely that, coupled with the recession, are the reasons we've seen the decline in emissions in the United States. It's being driven by two forces. One is primarily market forces that, frankly, again, we have this huge supply of natural gas that's been unleashed through fracking that's allowed prices to go down.

EILPERINIt's made it much more economical to build natural gas-fired plants as opposed to coal plants. You've also had regulation from the Obama administration, which, again, some -- many environmentalists have welcomed, many business interests have said is overreaching, which has really cracked down on emissions from coal-fired power plants and made it uneconomical. So, certainly, there's kind of a combination of things that are pushing that way.

EILPERINWhile, of course, you can certainly -- anyone, any academic could say that China should switch over to natural gas, I'd be very interested to see the economics behind that. They have tremendous coal reserves. They don't have the natural gas reserves we have. So to say that China is going to make the transition that the United States is in the middle of certainly would involve significant change in resource mixes or significant help from developed countries, which I've seen no indication that American taxpayers or others are willing to pay for.

REHMRichard Muller.

MULLERYeah. According to a report by the Energy Information Agency -- this is the official report -- they have 50 percent more natural gas reserves than the U.S. has. So they do have the supplies. I think we -- what we really need to do in the United States is to focus in -- on what I like to call clean fracking. I'm willing to admit that, yes, fracking has been bad in the past. It's polluted groundwater. Leaking natural gas is terrible 'cause it's 23 times more potent than carbon dioxide. So we have to do clean fracking.

MULLERWe could do this in the United States through regulation, I believe. Just make the fines really big. The question is we have to share our technology with China. This is going to take a big initiative. Whether it lasts 20 years, I -- my estimate, it's going to be more like 50 years. That's plenty of time for alternative technologies like solar and wind to really get to the point that China can afford them.

MULLERSo in this interim period, which could be quite long, natural gas will work, but we have to make it clean. And I think the tricky part is not, how do we make it clean in the United States, but how do we make it clean in China and the developing world?

REHMBut first we have to make it clean in the United States, Michael.

MACCRACKENThat's certainly true. Richard's number, when he says it's only 23 times as much as CO2, is based on its warming influence over 100 years. If you think about its warming influence over 20 years -- its lifetime in the atmosphere is 10 to 20 years, assuming -- it's 75 times as important as CO2. So methane has its effect early. So if we want to have -- if we want to slow down the warming now over the next couple of decades, we have to work on limiting methane. So you need very, very, very clean natural gas if you're going to have that.

REHMMichael MacCracken, chief scientist of the Climate Institute, and you're listening to "The Diane Rehm Show." I'm going to open the phones now. We have a great many listeners who'd like to take part in the conversation. First to Raleigh, N.C. Good morning, Bob. You're on the air. Thanks for calling.

BOBGood morning, Diane. Thank you for having me.

REHMCertainly.

BOBI'll be very brief. Two things. One is that I think your guests are pointing out a very big part, that climate change is really part of a overall symptom that is really how we are affecting the ecosystems around the world and how we are going to have to fundamentally change how we do things. But my real question is in regards to the political system. Mr. Ryan, who is recently named vice president's -- I guess I should say...

REHMThe running mate. Sure.

BOBYes. As Mr. Ryan was a very strong, strict client -- climate denial, and the question I have is how is that going to affect policy in the future, and really how is that going -- how that's going to impact really all our children and grandchildren?

REHMJuliet.

EILPERINThat's an excellent question. There's no -- there's certainly no doubt that if Mitt Romney and Paul Ryan are elected in the fall, that you will see a significant shift in terms of climate policy of the United States.

REHMAway from regulation?

EILPERINAway from regulation. I mean, the more -- while the caller is absolutely right that, for example, Paul Ryan has questioned, like many other elected Republicans, whether humans are contributing to global warming, he -- you know, this is not a top priority for him. But certainly there's no question what camp he's in.

EILPERINWhat's, of course, been more significant is Mitt Romney, who helped enact regulations in Massachusetts as governor that limited greenhouse gases in that state, has made a dramatic shift running this year, where late last year he switched from saying that humans were contributing to climate change to saying he simply does not know and does not know where the science is on that. So there's every reason to expect that you would see a pullback in terms of the regulation of carbon dioxide and some of these other activities.

REHMMichael.

MACCRACKENI'd say two things. One, many of these politicians are saying they don't believe in climate change. Well, let me say scientists don't come to their results because they believe in it. They come to it because of the evidence. The first thing we need to do is get people looking at what the evidence is. That can take some time. You can't just make a statement, but it can take some time. Prof. Muller invested a couple of years with his team to sort of get to that point, but that's the first point.

MACCRACKENThe second one is there are a range of kinds of policies. You can do it with incentives as well as opposed to just regulation. I mean, there's incentives to do it. Right now, there's a lot of incentives in Maryland around to go solar, and it's a very efficient and a good paying investment. I just did it. And...

REHMOn the -- OK. On the other hand, I have listened to an awful lot of people who talk about solar conversion to existing homes and buildings as something that is so expensive, that it's more likely you're going to see solar established in newer dwellings, newer homes. You're saying...

MACCRACKENI just don't think that's true. OK. So I have a 15-year-old home I put solar on. I got -- I mean, the way that it's set up right now with these major companies is you actually get a lease for 20 years of the equipment. They have payment options where you pay sort of nothing up front and a monthly payment, not unlike your present utility bill. You can pay a few thousand up front and have a slightly level -- have a level sort of bill. I paid for my system about $17,000 to put it up on the roof. I'm getting almost a 1 percent per month return on the investment because of my savings.

REHMJuliet.

EILPERINThere's no question that, for example, there has been a real uptick in these rooftop installations. It's been directly tied to government policy in the states and cities such as D.C., where there are financial incentives provided by the government. That's where it's economical to do it. There's no question that by switching over to a lease system, it's become much more affordable for people who can't afford to pay up front. But without some level of government support, the numbers just don't add up.

REHMBut look at huge buildings. Can huge buildings afford that kind of conversion? Isn't that going to cost?

MACCRACKENIt's happening all over New Jersey, for example. I mean, it would be interesting to hear what Gov. Christie has to say...

REHMI'm glad to hear that.

MACCRACKEN...about that because that's a state that's really worked very hard to do that.

REHMI'm glad to hear that. Michael MacCracken, Juliet Eilperin, Richard Muller. Short break. We'll be right back.

REHMAnd welcome back. We'll go right back to the phones, to Oklahoma City, to Carol. Good morning to you. You're on the air.

CAROLOh, good morning. Thank you. I would like to know from your panel what they would say to skeptics who say that scientists that support the idea that humans are mostly responsible for climate change are just in it for the research grant money.

REHMIn it for the research grant money. What do you think, Richard Muller?

MULLERWell, I don't think that's right. I think that many scientists are specialists. And they know a lot about glaciers or they know a lot about the atmosphere or something like that, and they will then sign a petition saying that we believe climate change is real. Unfortunately, I think they've done a lot of that prematurely. They really don't have the overview of the entire subject. And some of my friends, I walk up to them and say, did you sign the petition? They say, yes, I did. I'm a -- you know, he's a Nobel laureate.

MULLERAnd I say, well, what do you think about the issue of data selection bias? What do you mean? Well, what about the poor station quality? We've never heard of it. I think, unfortunately, there's been too much of a rush even among scientists to try to pick sides and be on one side or the other when, in fact, there are a lot of issues that really are wrong. I think many of the -- I've been to Washington and talked to the Republicans. Many of them seem to be more aware of the misinformation.

MULLERYou know, polar bears are not dying because of global warming, not yet. They may -- and I fear that they will in the future -- but it hasn't happened yet. Hurricane Katrina was not due to global warming. So many things that we attribute to so-called climate change are things where valid skepticism is still correct. And I would -- I think we need to respect the skeptics more because, in fact, I think most of what they're skeptical about is something we all still should be skeptical about. Global warming is real.

MULLERWe need to do something about it, but we need to do something about it rationally. But the idea that, hey, you walk outside and feel climate change is just not scientific. You have to get -- one-third of the temperature stations in the United States have showed cooling over the last 100 years. We have this on our five papers online. So it's not something that is easily detectable, and many people have been, I think, unfortunately brought on to believe that this is -- that the attack on climate signs is an attack on science. In fact, many of the issues are valid.

REHMMichael.

MACCRACKENWell, I think there are a couple of things. First, I guess I should say I'm in it because I've been volunteering for 10 years since I retired, so I'm not getting any government money. But I think that's really an insult to scientists. I mean, they're in it because they really care about issues, and they're just not in it for the grants. They'd go work on something else they thought was important if they felt that way or something. It seems to me the comment -- to come back to Richard's one -- is that it really depends on what the level of confidence you want is.

MACCRACKENIf you want absolute, very high, very high confidence that science usually wants so they don't make mistakes, like thalidomide and some other things, you're going to keep working on things and trying to resolve every single nit and everything. But we're in a place where things are going on and on and on. And in public policy, it's relative likelihood that matters. It's -- so you want to know, is it more likely this than that? And, overwhelmingly, the evidence is -- you know, indicates that it's human activities that are causing the problem, and that's what we have to deal with.

REHMYou know, I...

MACCRACKENThere's always going to be uncertainty.

REHMSure. I was amused by this week's New Yorker cover which shows Santa Claus out on an ice flow surrounded by melted ice. Is the ice melting?

MACCRACKENWell, yes, it certainly is. And there's actually an effect going on that isn't in the model. Uncertainties work both ways. I mean, it turns out that now, as the ice gets thin, if a big storm comes up, it can disrupt the ice. It can break it up, and that's going to lead to more of it melting. And so you're getting much more retreat. So uncertainties work both ways.

REHMSure. Juliet.

MULLERYeah. Diane? Diane...

EILPERINI...

REHMHold on, Richard. Go ahead, Juliet.

EILPERINI was just in the Alaskan Arctic a month ago and -- I went up there. And there's just no question that you talk to people, and they can chart -- I mean, first of all, there was just evidence that there's been a 40 percent reduction in the extent of some of the sea ice there, and satellite recordkeeping began in the 1970s.

EILPERINBut, again, I was spending time with Inuits in the Arctic, whose very lifestyles are changing because of changes in the ice and how they depend on it. And what's interesting is, when I sat down with the lieutenant governor, Mead Treadwell, a Republican, he said, you won't see us sticking our heads in the sand. We know the ice is going out. So in a state like that, which is really on the front lines, they're not questioning that, even though they're still having some debates about policies.

REHMRichard.

MULLERYou know, I worry that every time there's anything bad that happens, it's attributed to global warming and to human cause. Yes, the temperature rise is due to humans. But the rise has been two-thirds of one degree Celsius. It's been tiny. Is the Arctic melting due to global warming? You know, the evidence for that is very, very flimsy. I'm not even sure it's true. There are other things that affect the Arctic. We know the Northwest Passage, for example, was clear of ice in 1903 to 1906 when Amundsen and his crew took a wooden boat north of Canada.

MULLERSo there are cyclic things that happen. There are variations in the Gulf Stream, in the North Pacific. We may be going through one of these cycles here. When I was a kid, every time there was a bad hurricane, someone attributed it to nuclear bomb testing. So I think this idea that every time you see something bad you can attribute it to global warming is undermining the case for global warming.

REHMMichael.

MULLERAnd many Republicans when they see this, of course, they disagree. They're not dissenters. They're not deniers. They're just saying, no, that's not science.

MACCRACKENYou know, well, the -- I think the issue is it's not one or the other. I mean, global warming is just like, as some people have said, having a baseball batter with steroids or something. They're able to hit more home runs longer. You're having more active kinds of things happening. So Katrina, if you have warmer water, you're going to get more effects. Did global warming cause a hurricane to form? No.

MACCRACKENI mean, there's all kinds of eddies that came. But as those eddies develop into hurricanes, how much energy is available matters. And if you put more energy in, you'll have more effects, and so we're going to get more and more influence.

MULLERMichael, Hurricane Katrina was only a category-three storm when it hit New Orleans, and there were dozens of such storms that hit the Southern Coast. It didn't do much damage in New Orleans when it hit. But then the dikes leaked, and so it was flooded. But it was not a powerful storm. There were many, many, many such storms, and just New Orleans is a small target.

MACCRACKENBut you're judging the storm based on what the wind speed is. The issue is really -- I mean, the other major aspect of hurricanes is how much rain they put out and what -- and sort of how they push storm surges and, in some cases, whether they hit it low and high tide and what's happening with (unintelligible) so...

MULLERIt was only category three.

MACCRACKENBut you...

MULLERI mean, do we attribute this...

MACCRACKENWe've had...

MULLERYou say it was more energy.

REHMOK. One at a time, please.

MACCRACKENWell, we've had a tropical cyclone, which wasn't even a hurricane at all, that sort of parked itself over Houston and, I think, had, like, 24 inches of rain in 24 hours. That's going to cause a huge amount of damage, not from the wind but from the amount of rainfall that comes down. And what we're seeing is an increase in intense precipitation systems.

REHMAll right. I want to...

MULLERWe are not. We are not.

REHMWe are not.

MULLERI mean, this idea that we are seeing...

MACCRACKENThat's another database you'll have to go look at.

REHMOK. All right.

MULLERI have looked at it. I have.

REHMOK. Let's move on to Indianapolis. Good morning, Jeb. (sic) You're on the air.

JEFFHi. It's Jeff. I have a comment and then a quick question. But I always -- I'm a conservative, and I always thought that the climate change was due to the cyclical nature of the earth. We had dinosaurs at one point. Now, we don't. Now, the question I have is, have any of the studies dealt with population growth versus industrialization on the earth?

REHMJuliet.

EILPERINWell, certainly, there's no question that one of the reasons you're seeing rising emissions from the developing world is because they have larger populations, and they're growing at a faster rate. So certainly, I think, you know, there are bunch of different studies out there, but people would certainly say that there is a connection between -- it's not the question necessarily of absolute numbers, but how wealthy are these people getting and what are the result in carbon dioxide emissions that come from that? And that does contribute without question to overall emissions.

MULLERYes. Oh, I think so, and that's certainly true. But it also matters what the choice and energy systems that you make is. Even if we had, as I said a bit ago, just the 1 billion people in the developed world, if they choose fossil fuels, they can cause the earth to have significant climate effects by how much we're putting out. We're putting out, you know, five tons of carbon per person per year in the U.S., so that's much higher than what China is, which is down at one in a quarter or something like that. So our choices matter.

MACCRACKEN(unintelligible) -- I'm sorry. Our group actually did a scientific test of this, and we took our data and compared it just to a plot of population growth. And it wasn't a bad fit, but it wasn't nearly as good a fit as when we did carbon dioxide. So it's probably not some other effect of population.

REHMAll right. To Hunting Valley, Ohio. William, I gather you'd like some specific references.

WILLIAMYes. I'm a retired patent attorney, and I would like the pro-climate change people to cite some things that I can read, particularly emphasizing the urgency. I don't dispute CO2 is a factor. I question the urgency. And I'd also like them to give us some benchmarks. You know, what do we look for to know that their theory is correct?

REHMMichael.

MACCRACKENWell, on the first question, because of all the contention over this issue, this Intergovernmental Panel on Climate Change was formed in the late 1980s, and this carried out sort of for assessments of findings of international science over the last 20 years. It's in the process of a fifth one. That's one place to go. You can also -- I mean, I think they've put up climate.org website on here. If you go to climate.org, you'll see something -- where I've tried to say something in, I think, it's six-key points or something. On there, you'll see a place to push and get a sense of...

REHMAnd that's all specifically in regard to CO2?

MACCRACKENWith respect to human-induced climate change and why it's...

REHMOK. All right.

MACCRACKEN...and why it's urgent to go after that.

MULLERThis is very...

REHMAnd...

MACCRACKENBut there's a whole range of different things about what's happening.

REHM...he's also asking for benchmarks.

MACCRACKENWell, I think Jim Hansen has been a very interesting person in doing that. He made some of the early projections of that. He's quoted about his congressional hearing in 1988. He makes some projections about what would happen in the future, and he's re-looked at those. And it's very interesting that they've done -- I mean, climate is changing in a quite rapid rate. The other thing we test against is to try and understand against Earth history. We have had variations in the past.

MACCRACKENWe've had glacial cycling. We've had very warm period like the Cretaceous when the dinosaurs were there. And so what we're trying to do is understand what caused those to be different. Can we understand from the geological record what was forcing and influencing the change, and does that match up? And we've done pretty well back on through the glacial cycles on understanding that. And the only way to explain it is to have a climate that is pretty sensitive to CO2, about what is estimated by current mulling estimates and what the scientific main view is.

REHMAnd you're listening...

MULLERYou know, I would disagree on that latter -- I would...

REHM...to "The Diane Rehm Show." Richard, I know you want to get in on that.

MULLERWell, I wrote a book on paleoclimate, and I dispute that last point about the sensitivity of carbon dioxide showing up as it had in the past. But I do want to point out that our group has put five scientific papers online. People say that we announced it with the -- with my op-ed piece. But, in fact, no, we announced it by putting five detailed scientific papers on our website, which is berkeleyearth.org. And that is a good place to go for a reference to read about this material.

REHMAll right. I want to read to you an email and then ask you about this, Richard. It's from Ellen in Columbia, Mo. She says, "As a mother, I feel angry with Dr. Muller for having delayed action on this serious problem for so long by giving assemblance of scientific support to climate change deniers. He himself says his findings were in line with what other scientists were saying. Apparently, he felt, until he gave it his blessings, other people's evidence wasn't good enough."

REHM"And in the meantime, we've lost decades by moving in the wrong direction. I hope he is planning to put every ounce of his energy and time now into undoing the harm he has done to future generations." Have you been getting lots of feedback like that, Richard Muller?

MULLEROh, yeah. There are a lot of people there who confuse thought with rudeness. I'm a grandfather, and I really care about my granddaughter. But, no, we haven't lost the decades. The actions that were proposed in the past would not have done anything. The whole Kyoto Accord had no restrictions on China. The Copenhagen Agreement, which President Obama wisely decided not to sign, was going to have very, very small restrictions on China.

MULLERIt was going to limit their growth to about 6 percent per year in greenhouse gases, which would have been terrible. I think the things in the past that we have -- did not do were not things that would have solved the problem. They would have been feel-good measures that would make us look, you know, feel like, hey, well, global warming happened, but U.S. isn't at fault. We really have to address the numbers and recognize that if we can't do something to help China reduce, we're not doing anything. The things...

REHMJuliet.

MULLER...that we didn't do in the past don't count.

EILPERINJust a couple points following up, that President Obama brokered the Copenhagen Accord, and the U.S. did sign on to that, as did most of -- both industrial and developing world. Under that, we have pledged to reduce our emission 17 percent below 2005 levels, which we are on track to do in part because of the shift over to natural gas.

EILPERINAnd in the most recent set of climate negotiations that took place in December in South Africa, there was a change in the international understanding on climate where basically the developing countries, including China and India, did essentially break away from the long-standing divide between the obligations of the developing world and the developed world.

EILPERINNow, what will be subject to a new negotiation leading up to what would be a 2020 accord, and so we will see how much China and India do under this new formula. But, certainly, that has been a shift in the long-standing negotiation position.

REHMLast word briefly, Michael.

MACCRACKENWell, I think the main thing that's -- got stopped early on was research. President Carter started a major program on efficiency that got stopped by the next administration. It would have been wonderful to be improving things all through there. President -- I mean, after the Kyoto, there was a congressional action that said, you're not allowed to do research until Kyoto is presented. So we've stopped research. You have to have aggressive research.

REHMMichael MacCracken, chief scientist at the Climate Institute, Juliet Eilperin, national environmental reporter for The Washington Post, author of "Demon Fish: Travels Through the Hidden World of Sharks," and Richard Muller, professor of physics at the University of California, Berkeley, author of "Energy for Future Presidents: The Science Behind the Headlines." Let's hope we do begin a real move forward. Thank you, all. Thanks for listening. I'm Diane Rehm.