MR. KOJO NNAMDIFrom WAMU 88.5 at American University in Washington, welcome to "The Kojo Nnamdi Show," connecting your neighborhood with the world. Recent studies of the D.C. region warned that our infrastructure is facing greater risk due to sea level rise, and the peak of the cherry blossoms along the Tidal Basin is getting tougher to predict because of warming trends. But even as scientific evidence supporting climate change continues to grow, the number of Americans who believe in global warming has gone down.

MR. KOJO NNAMDIIt's quite possible that no scientist is more aware of this shift than Michael Mann. His research on climate change has been both revered, earning him a shared Nobel Peace Prize, and vilified with skeptics and deniers accusing him of fraud. Michael Mann joins us in studio. He is a professor at Penn State University, where he's also the director of the Earth Science Center. His new book is "The Hockey Stick and the Climate Wars: Dispatches from the Front Lines." Michael Mann, thank you so much for joining us.

DR. MICHAEL MANNThank you. It's a pleasure to be here with you.

NNAMDIIf you'd like to join the conversation, call us at 800-433-8850. You can send email to kojo@wamu.org, send us a tweet, @kojoshow, or simply go to our website, kojoshow.org, and join the conversation there. What role do you think politics should play in scientific research? 800-433-8850. Michael Mann, in choosing a career, you did not intentionally set out to embroil yourself in controversy. What did inspire you to make science in general, and climate science in particular, your life's work?

MANNWell, you know, as a child, I was fascinated by, you know, things like tornadoes and hurricanes and space travel and faster than light speed, and, you know, I was just -- I loved science. I loved anything that was vaguely scientific and, ultimately, ended up spending a lot of my time in high school -- actually, while other people were out having fun, I'd be trying to solve problems on the computer.

MANNAnd I decided to major in science as an undergraduate at Berkeley. I double-majored in physics and applied math and went on to start doing some research in theoretical physics. And, over time, I realized that I was sort of being funneled into increasingly sort of more detailed and smaller problems than I had originally imagined than what had got me excited, the sort of big picture scientific questions that had gotten me so excited about, you know, science in the first place.

MANNAnd I was midway through my Ph.D. in physics when I realized that there was this fascinating problem that required, you know, the sort of math and physics that I had learned that was immensely important -- understanding how Earth's climate system works. And I decided, hey, this sounds like a good way to apply, you know, the math and the physics that I've learned to a big picture, real world problem that matters.

NNAMDIYour dad, it's my understanding, was a math professor. Did he have any influence on your orientation towards math and science?

MANNYeah, I'm sure. You know, as I was growing up, I was always, you know, I'm -- I would -- it's fair to say that there was a lot of positive reinforcement when it came to all things math and scientific.

NNAMDIThe title of the book "The Hockey Stick and the Climate Wars," what does a hockey stick have to do with climate change?

MANNThat's a good question. I was actually up in Canada talking about this, and they were -- they love talking about hockey up there. But what the hockey stick actually is is a term that was applied by another scientist to a curve that my co-authors and I published back in the late 1990s. We only have about 100 years of widespread thermometer measurements, and those thermometer measurements tell us that the globe is warming.

MANNIt's warmed by about a degree-and-a-half Fahrenheit. As you alluded to earlier, we can see that warming and the associated changes in the advance of the -- you know, the blossoming of the cheery trees, the Tidal Basin here in Washington, D.C., so we know the globe is warming. We know the climate is changing. But, with only about a century of widespread thermometer records, there's always been this question: Well, you know, how unusual is that?

MANNIs that just a fluke? Does the globe often warm and cool by similar amounts, or is there something unusual happening? And so we turned to what we call proxy climate data. These are things like tree rings and corals and ice cores that are indirect measures of climate that allow us to try to extend that record back in time. And, back in the late 1990s, we performed an analysis using these data to estimate how temperatures had changed over the past 1,000 years. And what we found was that the recent warming was indeed without precedent, as far back as we could go, which was 1,000 years.

MANNAnd the overall shape of that sort of slow cooling into the little ice age before you get to that abrupt warming of the past century sort of looks like a hockey stick.

NNAMDIWell, how was that graph intended to be used, and how has it been used?

MANNWell, you know, interestingly enough, when we were -- first did this research, we were actually not that interested in the average temperature at that one curve. We were more interested in trying to understand how the El Nino phenomenon had changed in the past and what pattern of influence volcanic eruptions had had on the climate, what we could learn about the climate system from studying the past.

MANNIt was almost a byproduct that we produced that curve from our analysis, but it sort of took on a life of its own. It was featured prominently in a very important report of the Intergovernmental Panel on Climate Change and their summary for policymakers. It sort of became an icon in the climate change debate, and that's when we found ourselves at the center of this larger raging debate about climate change.

NNAMDIAnd that graph has been used in a number of ways for and against the arguments about climate change. In case you're just joining us, we're talking with Michael Mann. He's a professor at Penn State University, where he's also the director of the Earth Science Center. His new book is called "The Hockey Stick and the Climate Wars: Dispatches from the Front Lines." And we're inviting your calls at 800-433-8850.

NNAMDIWhat questions do you have about the science of climate change? 800-433-8850 or you can send email to kojo@wamu.org. As evidence pointing to human-caused global warming really started to mount, you say that the push against it took a page from the playbook of so-called big tobacco.

MANNWell, that's right. What -- it turns out that our work, you know, the hockey stick and other sort of estimates like it aren't the pillar of evidence for the reality of human-caused climate change that our detractors like to make it out to be. There is a vast array of independent lines of evidence that tell us that the globe is warming, the climate is changing, and human activity is responsible for most of the changes that we're seeing.

MANNBut those looking to discredit the science will often try to find some small detail to pick at and to make it seem like the science some house of cards, in the case of climate change, a house of cards that rests entirely on this one-decade-old study by my collaborators and me. And, in fact, that's not the case. The science is much more like a puzzle that's mostly filled in, and there are few missing pieces that we're still trying to figure out.

MANNBut there's no way that you could rearrange the pieces of that puzzle and come to a conclusion that contradicts the basic facts that we are warming the planet as we continue to burn fossil fuels and elevate greenhouse gas concentrations in the atmosphere. So what those looking to discredit the science have done is to try to make it seem like all the science depends on one study and, indeed, one person, me.

MANNAnd they've attacked me quite vociferously, much in the way that those looking to, you know, discredit the science of evolution like to call it Darwinism to make it sound like it's all about one, you know, evil individual -- Charles Darwin -- rather than the thousands of scientists who have independently validated his conclusions over the past century-and-a-half.

MANNSo, unfortunately, because our work sort of became an icon in the climate change debate, those who are looking to discredit the science of climate change, in many cases because of their, you know, advocacy for special interests who don't want to see us shift away from our reliance on fossil fuels, they've really sort of resorted to some pretty remarkable tactics in their efforts to discredit me and to discredit my colleagues.

NNAMDIIs that where the comparison with so-called big tobacco comes in because the general perception, of course, probably the truth, is that the tobacco industry for a very long time tried to oppose the science that indicated that tobacco was a cause of disease and lung cancer in human beings?

MANNYeah. Absolutely. And they created lavishly-funded think tanks that would advocate for their point of view that the science was grossly uncertain, that the link hadn't been established. They would fund scientists who were willing to advocate for their point of view, who were willing to attack mainstream science based on what were often very spurious and flimsy arguments.

MANNAnd so there was this sort of network of -- or pseudo-scientific groups, front groups, and even individual scientists for hire, who were employed to try to discredit the linkage between smoking cigarettes and lung cancer and other adverse health effects because the findings of science were inconvenient to powerful vested interests. In that case, it was the tobacco industry. Today, we're talking about the challenges faced by the fossil fuel industry.

NNAMDILet's talk about that for a second...

MANNYeah.

NNAMDI...because, while there are industries, like the aforementioned fossil fuel industry, that have a stake in delegitimizing climate change science, there are other industries that stand to benefit -- solar and wind power, for example. Is it possible not only to keep industry special interests out of science -- but I am betting that a lot of people claim that you are funded and backed by the businesses that support alternative sources of energy. Are you?

MANNWell, I'm not. My funding comes from government science funding agencies. They fund my research. And that's the way most scientists are funded.

MANNIn the case of, you know, climate change, you know, the fossil fuel industry, it's unfortunate that it's become so polarized because, you know, there are those who, you know -- and it's understandable that there are -- you know, there are elements within the fossil fuel industry that might feel quite under attack themselves and by those, you know, calling for dramatic changes in how we go about getting our energy -- switching away from fossil fuels to alternative energy sources.

MANNAnd, in reality, we're going to have to go -- undergo a transition. You know, we can't stop cold our reliance on fossil fuels. But what we can do is begin to incentivize other forms of energy production and internalize the cost of emitting carbon into the atmosphere in the economic decision-making process so that the incentive structure pushes us in the direction that we need to go. The rest of the world is doing it. And the U.S. is falling behind. You know, China, India, they're investing in alternative energies 'cause they see that that's the future of the economy.

MANNAnd it's a shame that we're still having this silly debate about whether climate change is even real rather than having a worthy discussion of how to confront the challenge.

NNAMDIBefore I get to the phones, environmental activists has -- have long been derided as watermelons -- green on the outside and red on the inside, the implication being that they are, at their core, socialists first. Do you consider yourself an environmental activist?

MANNNo. And, you know, I'm -- sometimes, I'm accused of being an advocate, and I will proudly wear that mantle. I am an advocate for the policy discussion being informed by an honest and an accurate assessment of what the scientific evidence has to hold. And I don't think any scientist should be ashamed of advocating for having a good faith discussion that's based on our best scientific understanding.

MANNAnd it's really unfortunate that we've -- you know, that it's this partisan divide that has emerged in the debate over human-caused climate change because, after all, we all care about our children and grandchildren. It doesn't matter whether you're a Democrat or Republican. And, you know, the decisions we're making today have -- will have profound implications for future generations.

MANNAnd if we don't make the right decisions, we are potentially leaving our children, grandchildren, a legacy of a degraded planet. And it doesn't matter if you're a Democrat or Republican. We should all care. We all do care about our children and grandchildren.

NNAMDILet me see how I can put this diplomatically. Are you a socialist? Or I should it put it another way. Does your philosophical orientation influence the scientific work you do, or vice versa?

MANNNo. And my hope would be that it's never true for a scientist that their political persuasion influences the way they do their science. And -- while I won't discuss my own politics -- I'll leave that aside -- what I can tell you is that some of my closest colleagues and leading climate scientists who talk passionately about the challenge that we face, many of them are actually registered Republicans, some within my own department. Some of the more prominent climate scientists around the country are actually registered Republicans, and they recognize that this isn't a political issue.

MANNIt's about what the science has to say, so, you know, I do think it's unfortunate that it's become polarized along partisan lines, and, hopefully, we get away from that and have a good faith debate about what to do about the problem.

NNAMDIYou've said that climate change should not be a political issue -- you've just reiterated that -- and that it wasn't that long ago that it was not a political issue. So why do you think it has become so politically charged?

MANNYeah, it's difficult to say, and I'm -- you know, I'm not a historian of science. But what I can tell you, just over the time period since I got into this field, what I've seen is that certain prominent politicians, who are, you know, well -- you know, whose campaigns are funded in substantial part by the fossil fuel industry, have increasingly seen themselves as advocates for industry rather than advocates for the people. And so we've had, you know, prominent politicians like Sen. James Inhofe, who has a book out right now, claiming that climate change is an elaborate hoax.

MANNAnd, apparently, the -- you know, the glaciers and the sea level and ice sheets have played along with the hoax. It's -- you know, it's just unimaginable that thousands of scientists around the world could possibly agree to create a hoax of this magnitude. You know, the problem is real, and it's unfortunate that there are some who do want to bury their head in the sand. And, in many cases, you know, I think they're seeing themselves -- they're primarily working as advocates for narrow special interests rather than advocates for the people. And that's really unfortunate.

NNAMDII wanted to look where -- on the left also, there are questions about science. People on the left who oppose, oh, one thing or another and left, in particular, people who oppose what's being done by the agricultural industry will say, this is not natural. Even though the science does permit it to happen, it shouldn't be happening. It happens, it would appear, both on the left and on the right.

MANNAbsolutely. I think there are abuses. And as a scientist, I've seen abuses on both sides of the spectrum. I have seen instances where the science was -- the implications of the science were overstated, where claims were made by those advocating agenda that were too strident, that weren't supported by the science. And that puts scientists in an awkward position because we can't -- you know, we can't back those up when extravagant claims are made that don't stand up to the rigor of what the science has to say. We have to distance ourselves.

MANNAs scientists, ultimately, we have to be advocates for the facts, making sure that the discourse is informed by the facts. And so we -- I have helped -- I co-founded a website called RealClimate about five years ago, or seven years ago now, actually, that was aimed at sort of taking the current state of understanding of the science, a group of scientists who work in the field and talking about the current state of understanding of the science in a way that sort of -- that people on the street could appreciate.

MANNAnd we have called out abuses of the science on both extremes, both when the science has been overstated and when it's been misrepresented or, you know, argued to be a hoax. And so we try to be even-handed in the way we cover that.

NNAMDIGot to take a short break. When we come back, a lot of you have called, so the phone lines are busy. You may want to contact us by email to kojo@wamu.org. Go to our website, kojoshow.org. Join the conversation there. Send us a tweet, @kojoshow. Have you seen evidence of climate change in your backyard or neighborhood? 800-433-8850, if you can get through. I'm Kojo Nnamdi.

NNAMDIWelcome back to our conversation with Michael Mann. He is a professor at Penn State University. He's also the director of the Earth Science Center there. His new book is called "The Hockey Stick and the Climate Wars: Dispatches from the Front Lines." Before we get to the phones, obviously, there's one other issue we have to discuss.

NNAMDIA year after Climategate, your work -- Climategate, of course, being another issue that we haven't discussed yet -- but your work at the University of Virginia came under fire when Atty. Gen. Ken Cuccinelli sought access to your research documents, including your email, to determine whether you had used fraudulent data to secure taxpayer-funded grants. Why you?

MANNWell, it's -- you know, it's an unfortunate episode, and I think what those looking to discredit the science of climate change have increasingly resorted to, you know, theft of private emails -- or in this case using the authority of the Office of the Attorney General to demand that the University of Virginia turn over private emails between me and 39 different scientists -- in, you know -- what those looking to discredit the science have been trying to do is to just find something they can use to try to embarrass us or to take out of context to try to make it sound like the science has been fudged, like climate change is indeed an elaborate hoax.

MANNAnd, you know, there are some examples from the stolen emails where people took a term that scientists use freely in a very innocuous sense. We often -- if somebody got their start in math and physics, we use the term trick in math and physics to describe a clever approach to solving a problem. There's nothing wrong with a trick. It's actually really good if you can come up with a clever trick to solving a problem.

MANNAnd it's so easy when you, you know, seize private emails and scientists are talking to each other in jargon, technical jargon, to take a word like that and then say, aha, see, look, they're admitting...

NNAMDIWe knew it was a trick all along.

MANNAnd so, unfortunately, it seems like the attorney general was engaged in a campaign to just try to find more material like that that he could use to try to misrepresent the scientists. And we were -- you know, we were pleased that the state supreme court did reject his case with prejudice.

NNAMDILet's stay with those emails for a second because you had also written about containing data from a medieval warming period, and that made it sound as if the scientists were trying to hide something by containing it. What did that phrase mean?

MANNYeah, that's another great example of you take some words out of an email and you can try to make it sound like something completely different from what it was. So I was actually referring to words that have been used by another scientist, and what he was talking about was -- as I talked -- mentioned earlier, the work that I did back in the late 1990s, we were able to extend temperatures back about 1,000 years. And that puts us in a period that's sometimes called the Medieval Warm Period where temperatures were relatively warm.

MANNI doesn't put us far enough back that we can see where that period started. Was there an isolated period where it was warm? And so what we were talking about in that email was actually trying to extend these reconstructions with the data we have back farther, maybe even 2,000 years, so we could entirely contain that medieval interval and see, you know, of what duration it was and of what magnitude it was.

MANNAnd so, unfortunately, it's just so easy to -- you know, there's a famous line -- I believe it's attributed to Cardinal Richelieu -- give me six lines by the most honest of men, and I will find something in them to hang him on.

NNAMDIWe talked with the Virginia Atty. Gen. Ken Cuccinelli back in 2010 on the broadcast on Fridays we call "The Politics Hour," and guest analyst -- the other voice you'll hear in this conversation is guest analyst Paul West of The Baltimore Sun about why the attorney general was pursuing this.

ATTY. GEN. KEN CUCCINELLIWe're not investigating his academic work. We're -- that subpoena is directed at the expenditure of dollars.

MR. PAUL WESTOK.

CUCCINELLIWhether he does a good job, bad job or I don't like the outcome -- and I think everybody already knows that, you know, his position on some of this is one that I question. But that is not what that's about. It's about state tax.

WESTRight. OK. But you -- we don't want to litigate this particular issue here 'cause we can't. But you questioned, as you just say, his conclusions, that the Rachel Levinson, the senior counsel of the American Association of University Professors, has said that your action "had echoes of McCarthyism." And I wonder what your reaction is to that.

CUCCINELLIWell, I think the reaction is that when you say something like that, you hope to provoke a reaction. You know, I'm charged as attorney general with dealing with potential fraud with taxpayer dollars. Last year, we recovered over $40 million in my office doing this. And it is a regular activity, even if we don't always use CIDs to do it, which is the...

WESTAnd do you think the amount of money that you will recover if you're successful in this case will be greater than the amount of money you will spend in going after this expenditure that you consider a possible fraud?

CUCCINELLIThe amount of money, for your listeners, is about a half million dollars spread out over multiple grants. And it is one unlike virtually every other expenditure in state government where there's at least some information out there that has been brought to us that indicates there may be problems in terms of whether or not the money is spent for what it was requested for. That's where it's directed.

NNAMDIVirginia Atty. Gen. Ken Cuccinelli. I do have to point out that earlier this month, the Virginia Supreme Court ruled on the case, deciding that the attorney general did not have the authority to seek the release of the documents. Two questions here. It's one thing to be accused of flawed research, another to be accused essentially of theft, of fraud.

MANNYeah. And, you know, it's unfortunate that, you know, you have the attorney general of a state like Virginia, a great state like Virginia, making, you know, outrageous and dishonest allegations against not just me but other scientists 'cause he wanted email correspondences with 39 different scientists. Now, what the court -- the initial finding that he challenged -- and it was ultimately rejected by the supreme court of the state. The initial filing, the finding by the judge was that in the 40 pages of his CID, he did not anywhere provide any evidence of any fraud at all.

MANNAnd, you know, I don't know how many millions of dollars of Virginia taxpayer money that he actually spent on this. But it's really unfortunate that all that money was wasted on this frivolous lawsuit that the University of Virginia, Thomas Jefferson's great university, had to delve into its resources to defend itself.

MANNAnd meanwhile, we could have been, you know, the state of Virginia could have been using that money to, you know, start to deal with the measures that will be necessary to adapt to sea level rise that's going to influence the Chesapeake Bay and the coast of Virginia, so it's really unfortunate.

NNAMDIOn to the telephones now. And thank you for waiting, Rick in Bethesda, Md. You're on the air. Go ahead, please.

RICKHi. I have two points, first of them being that you could probably draw a graph between the degree of scientific illiteracy that appears to be a trend in this country and the non-belief in global warming. And I think we're also fighting a psychological battle here. I think what -- when people hear that global warming is a reality, they (word?) the future in which the number of jobs and the number of industries decrease and their economic survival may be threatened as a result of it.

NNAMDIDo those implication…

RICKThanks for taking my call.

NNAMDIThank you very much for your call, Rick. Do those implications concern you at all, Michael Mann?

MANNYeah, the caller makes some really good points. You know, I think many people do feel threatened by -- the changes that are projected are threatening, but also the -- you know, the degree of the challenge, the magnitude of the challenge that we're going to have to undertake if we are going to shift away from our current energy infrastructure and build a new energy infrastructure that allows us to grow the economy as well as, you know, save the environment.

MANNAnd I think what's important to realize is that we can do that. It isn't -- you know, it's sort of a false choice. You know, it's often framed by those who articulate the case for inaction, who don't want to do anything about the problem, is that it's a choice between the economy or the environment. And it's not, you know? In fact, we can protect the environment by investing in technologies that will grow the economy. And other countries recognize that and are already doing that and U.S. is falling behind.

NNAMDIOn to the telephones again. Here is Mike in Washington, D.C. Mike, your turn.

MIKEHi. I think the information you're providing, I think, is going to alert people to the issue. I think, however, you're overstating the people who are -- the scientists who are taking the position that man is not a major cause of global warming. I think your outright refusal to say that maybe their statements are correct do not -- does not contribute to the full understanding of the issue for Kojo's listeners.

NNAMDIYou want to be more specific than that, Mike? Or I'll simply have Michael Mann respond.

MIKESure. I think there was a study by a number of Australian scientists in 1999 that their conclusion was that man was not responsible for the majority of global warming. The United Nation's task force on global warming changed their views a few years ago in terms of the severity of global warming and admitted that their initial report that a number of glaciers in Greenland were reducing was not true.

NNAMDIMichael Mann.

MANNYeah. Unfortunately, that's -- the gentleman -- I appreciate his point of view and his concerns. But he doesn't have his facts quite right. What -- it's -- you know, you can forget about the United Nation's -- the Intergovernmental Panel on Climate Change. Look at the National Academy of Sciences, founded by Republican President Abraham Lincoln back in the 19th century as the highest authority in the land to advise the government on matters involving science matters and policy involving science.

MANNThe National Academy of Sciences has stated affirmatively that human-caused climate change is indeed the consensus of the scientific community. The national academies of all of the major industrial nations in the world have concurred with that finding, that humans are warming the planet and changing the climate, and if we continue on the course that we're on, we are likely to see potentially catastrophic consequences in the future. Now, it's always easy in science to find a maverick or even a group of mavericks.

MANNYou can find a small group of people who are willing to say just about anything, but that's not the way science works. It doesn't -- it isn't based on individuals and opinions. It's based on evidence. It's based on solid reasoning. It's based on appropriate establishment of hypotheses and testing of hypotheses and validating of hypotheses. And what you do is you look at the collective evidence across the scientific community, what's being published in the peer-reviewed literature, what the various assessments reports have to say.

MANNAnd there is literally no question, when you look at where the -- what the science has to say that, you know, human-caused climate change is real. It's happening, and we can, you know, bury our heads in the sands and pretend that it's a elaborate hoax like James Inhofe likes to argue, or we can begin having the good faith discussion necessary to talk about how to deal with it.

NNAMDIWhat about people who say, wasn't there a time when the majority of scientists in the world thought that the world was flat?

MANNWell, you know, it's -- in science -- the wonderful thing about science is that it has this self-correcting mechanism, and that's skepticism. Scientists should be skeptics. All good scientists are skeptics. We demand proof. We demand solid evidence in reasoning, and hypotheses have to be revalidated. They have to be independently retested, and conclusions have to be reproduced in subsequent studies. That's the way science evolves. And, you know, every once in a while, science gets something wrong, but the wonderful thing about the scientific process is we eventually get it right.

MANNAnd sometimes it takes a little longer than we'd like. And that was true with the plate tectonics, took decades for the scientific community to accept the evidence. And that's been true throughout scientific history. But, in the case of climate change, it's not the sort of house of cards that it's -- that detractors like to make it out to be, like it all depends on one small number of studies. It's a puzzle, you know, that's mostly filled in. We know the greenhouse effect is real. We've known about it for nearly two centuries.

MANNYou increase concentration of greenhouse gasses in the atmosphere. The surface will warm. It's basic physics and chemistry. And, again, there's no way around that.

NNAMDIPolitics, policy, science, economics all tied up in the arguments over climate change. But you say that, for you, it boils down to something else: Ethics.

MANNIt does. I mean, we often frame it as a scientific problem or a policy problem or a problem of economics, cost-benefit analysis, and I think, not often enough, do we frame it for the problem that it ultimately really is. It's a problem of ethics. I have a 6-year-old daughter. I'm sure many of your listeners have children and grandchildren, and we all care about the planet that we leave our children. Now -- again, we can bury our heads in the sands and pretend that the problem doesn't exist.

MANNOr we can begin taking the actions necessary to ensure that we leave our children and our grandchildren the same planet that we grew up on. And there's still time to do that. It's not time for despair, but there is a very real urgency. We have to begin transitioning away from our reliance in fossil fuels if we're going to stabilize greenhouse gas concentrations below the levels that really start to represent a dangerous threat for humanity.

NNAMDIHere's Arthur in Washington, D.C. Arthur, you're on the air. Go ahead, please.

ARTHURThank you. And thank you for your very important research and also for being a scientist who is able to communicate across to the general public. I've been listening to you talk, and you're doing a great job. One of the things -- and I work in the field on that advocacy. And one the things that I'm concerned about is where we're at, and, I guess, the question is -- I've heard reports.

ARTHURI've seen it in a UNEP report, came out a couple of years ago, that we're starting to go over the tipping points. And looking at the way that global trends are headed with greenhouse gas emissions and the warming trend, is it too late?

MANNWell, you know, the thing about tipping points is you don't know that you've crossed them until you get there. And there is a worry that there are tipping points that sort of loom in our potential future, that -- thresholds we could cross where we -- you know, we commit to the melting of the major ice sheets. Or we begin to release large amounts of methane, also a very potent greenhouse gas, into the atmosphere because of the melting of permafrost.

MANNAnd these are things that scientists study, and it's -- these are things that we worry about. What we do know, however, is that there is still time to stabilize CO2 concentrations at a level where we believe we probably don't risk crossing those tipping points. Again, we don't know exactly where they are. But if we are able to limit warming to less than another degree Celsius over the next century, we can probably avert what might reasonably be called, you know, dangerous human influence on our climate and on the planet.

MANNAnd it's not going to be an easy thing to do. Our emissions currently lie well above the trajectory that would be necessary to stabilize CO2 concentrations below that dangerous limit. If we're going to do that, we really need to bring our global emissions to a peak within the next few years. We need to ramp them down so that they're well below, you know, late 20th century levels by the middle of the century. And so it won't be easy to do that, but we can certainly do it. And we've risen to the challenge before.

MANNPeople sometimes say, well, it's a futile problem. There's no way we can solve a global environmental threat like climate change. But we've done it before. We did it with ozone depletion. We did it with acid rain. We can do it with climate change. But we have to start working towards that solution quickly.

NNAMDIArthur, thank you very much for your call. We've got to take a short break. When we return, we'll continue our conversation with Michael Mann. His new book is called "The Hockey Stick and the Climate Wars: Dispatches from the Frontlines." We're taking your calls at 800-433-8850. If you question whether climate change and global warming trends are real, you can call us to tell us why. 800-433-8850. I'm Kojo Nnamdi.

NNAMDIWelcome back. We're talking with Michael Mann. He is a professor at Penn State University where he's also the director of the Earth Science Center. His new book is called "The Hockey Stick and the Climate Wars: Dispatches from the Frontlines." You spend a lot of time doing community outreach these days, and people may be surprised to learn where you find some of your most receptive audiences: In church.

MANNThat's right. I enjoy talking to church groups, religious groups, people of faith. There is, you know, this principle of stewardship that runs through the -- you know, the faith community. It's a very important principle in the Bible that it is our responsibility to protect the earth, as stewards of the earth. And I think that many in the religious community value that greatly, and they recognize the challenges that we are facing right now with the planet. Of course, you know, climate change is just one of many global environmental challenges that we are facing.

MANNAnd it gets back to this issue of ethics. Whether you want to call it, you know, a biblical principle of stewardship or an ethical principle of what we owe future generations, it's pretty clear that the decisions we are making today will have profound implications for decades and centuries to come. And that's just because of the long timescales associated with elevating greenhouse gas concentrations of the atmosphere and the climate changes that that sets in motion. And so we have an ethical responsibility to make sure that we leave our children an un-degraded planet.

MANNAnd I think many in the religious community recognize that. And they're passionate about this issue, and they want to learn more. They want to understand the facts better so that they can help communicate the facts to others.

NNAMDIWhich means, of course, that there's also a divide in the religious community along these lines.

MANNYeah, and that's unfortunate. You know, there have been, you know, some who, in the religious community, who appear to sort of have allied themselves politically with sort of some of the same special interests that are opposed to the regulation of greenhouse gasses. And that's an unfortunate alliance, in my view, because, again, there couldn't be a more fundamental principle in -- you know, that pervades the faith of the world than the principle of stewardship.

NNAMDIOn to Elaine in Middleburg, Va. Elaine, you're on the air. Go ahead, please.

ELAINEKojo, thank you. This is really important. I wish the professor was on every radio station, every television station in America. I think it's a generational thing, this whole climate change. I've been in meetings in Richmond about mountaintop removal. The lines are divided. You've got the Chamber of Commerce, and then you've got the other side. And each of them has their own agenda. And the ones -- the younger ones believe there is climate change, believe we have to do -- stop the destruction of the mountains, and the others, no. I've been also...

NNAMDIUh oh. Elaine, where are you? Elaine's call seems to have dropped off. But I understand you spoke to students at Bishop O'Connell High School in Arlington this morning. When you speak to young people and to students, what kinds of questions do they have about climate change?

MANNWell, actually, I don't speak until tomorrow morning, and I'm really looking forward to that. And I have spoken to schoolchildren before about this issue, and -- you know, and it's an issue that the caller nicely underscored, that there is this generational divide. I think, you know, the younger generation gets it. They understand that there are profound changes that are taking place in our climate that will have implications for their future.

MANNThe problem is that we don't have time to wait for them to grow up and be in the position to actually make the policy decisions that will ensure that we preserve the earth's climate. We have to be making those decisions now. And one of the things that I hope is happening -- and I see it happening -- sometimes the older generations actually learn from the younger generations. And I've seen children with their parents together at exhibits, at zoos, where, you know, they're talking about the challenges to the environment.

MANNAnd I think that, in some of these cases, the parents are learning something from the children, and those interactions are extremely valuable.

NNAMDIOn to the telephones again. Here is David in San Francisco, Calif. David, you're on the air. Go ahead, please.

DAVIDHey. How are you, Kojo and Michael? You know, I -- it's unfortunate, Kojo, that you used that example about the flat Earth. If I remember right, Galileo, when he expressed his recognition that the earth revolves around the sun, he was locked into a dungeon for 17 years and forced to sit on a sawhorse until it turned his gonads into mush for months on end. So the scientists of the day, so to speak, were dead silent once they realized what would happen to them if they spoke up. So, along those same lines...

NNAMDII love it when our historians call. Go ahead, please.

DAVIDSo if you were to look at the polluters, the polluters of today and of the past, obviously, the cancers and the high-dollar expense of fixing the earth is going to come out of their pocket if we recognize that global warming is happening. They have a vested interest in censoring reality so that they don't have to pay for the cancers and the medical costs that they've incurred. And so looking at -- currently, just a week or so ago, we had massive tornadoes that ran from basically the Gulf of Mexico, all the way up into Pennsylvania.

DAVIDAnd I call a lot of radio talk show stations, and I don't hear any sign that it was a campaign issue in any of those states that they visited. Alabama, it was not discussed. Alabama and Mississippi, just the other day, didn't discuss the Gulf of Mexico and what BP did to their shoreline. They are not talking about it because the polluters do not want to pay for the damages that they've incurred on us.

NNAMDIOur historians are also up on current affairs, Michael Mann.

MANNWell, you know, the reader, you know, makes -- the commenter makes a really important point, you know, that, unfortunately, our public discourse, to some extent, has been hijacked by those looking to cloud the debate, by those looking to confuse the public about the reality of the problem. There was a memo that was leaked back in 2002 by a prominent political pollster. It wasn't supposed to get out into the public domain, but it did leak out.

MANNAnd it was describing a strategy for opponents to regulating carbon emissions, for how they could still exploit the narrow window that existed as far as the public's understanding of the science, that that window was closing. The public was beginning to understand that this problem is real. But there was still a narrow window of opportunity to manufacture uncertainty, to convince the public that the science is grossly uncertain -- uncertain enough, that it isn't -- you know, that it might be risky to take actions to deal with the problem.

MANNAnd, unfortunately, that has been more or less the way many of the politicians, who are acting as advocates for the fossil fuel industry, have treated the problem in recent years, by claiming that the -- you know, the climate change is a hoax, by claiming that dealing with the problem by investing in alternative energies that get us away from our dependence on carbon will destroy the economy when what we're seeing in the rest of the world is other countries growing their economy by investing in these new technologies.

MANNAnd so it's so unfortunate that the discourse on this issue has become so poisonous. It's become so politicized. And I'm afraid that it's part -- it's symptomatic of a larger problem right now in our public discourse. And our current -- you know, this silly debate about whether climate change is real is, unfortunately, a symptom of that larger problem.

NNAMDIAnd that window of opportunity you talked about, according to our emailer Shelly, David and Michael, is facilitated by the language we use. Don't want to quibble here, but here's what Shelly writes, "Can you please ask your guests why people persist in calling his -- this phenomenon global warming" -- the term David used -- "instead of climate change? Climate change, in my opinion, is both an accurate name and eliminates a line of argument for skeptics, who cite colder-than-normal weather patterns as reason to deny the science."

MANNWell, you know, it's an interesting point. In that leaked memo that I referred to, one of the aspects of the memo was coaching opponents to regulation on their use of language, on what terms they could use to make climate change, for example, sound less threatening. Now, it turns out that if you want to talk about it from a purely technical perspective, the larger issue is climate change. We are warming the planet by increasing greenhouse gas concentrations.

MANNBut we're changing all sorts of other attributes of our climate and our weather, whether it's the incidents of heat waves, of extreme heat, the severity, the maximum intensity of hurricanes, the prevalence of drought, the persistence of drought, rising sea levels, shifting rainfall patterns, shifting wind patterns, shifting ocean currents. So there's a whole array of changes that are -- that pumping the CO2 into the atmosphere is engendering. And the warming of the planet is just one of many of the changes that we've set in motion, and some of the other changes, for example...

NNAMDISo the two terms are not necessary interchangeable.

MANNThey're not. Global warming is just one aspect of climate change. And the climate changes that might impact us most severely in the U.S. relate, for example, to shifting water resources, where we're likely to see increased drought over the Southeast U.S. and especially the desert Southwest, which is already struggling to meet its water needs with the limited water resources it has. The models project that drought gets even worse there. And so there's a whole array of challenges associated with climate change, and the warming of the planet is just one of them.

NNAMDIAnd I'm afraid we're running out of time. But you mentioned earlier that the division we have on this issue is symptomatic of a broader division in society at large. So how do communities and governments cope with the results of climate change if this division persists?

MANNWell, you know, a lot of municipalities, cities are actually -- and states are trying to pass legislation to deal with the problem. And so there is an effort right now to try to solve the problem in the opposite way. We usually think about solving these problems, rather than from the top level of government down, from the lowest levels of government upward.

MANNAnd I think what we're likely to see is California, some of the West Coast states join with some of the states in the Northeastern U.S., we will see increasingly powerful alliances of states that are going to demand that we act on this problem even, potentially, before we pass, you know, federal legislation to deal with the problem.

NNAMDIMichael Mann, thank you so much for joining us.

MANNThank you. It's been a pleasure.

NNAMDIMichael Mann is a professor at Penn State University. He's also the director of the Earth Science Center there. His new book is called "The Hockey Stick and the Climate Wars: Dispatches from the Front Lines." Thank you all for listening. I'm Kojo Nnamdi.