In the most recent public polling on climate change, 83% of Americans agreed with the statement: “global warming will be a very or somewhat serious problem in the future.” And yet, spin-doctors and conservative naysayers continue to sow doubt about the legitimacy and credibility of our warming planet, as is so vividly displayed in Robert Kenner’s new documentary Merchants of Doubt. Tracing the corporate PR tricks of the tobacco industry to the climate change deniers of today, the film presents a bracing view of the ways that demonstrable and widespread scientific knowledge can still be labeled as untrustworthy. Once upon a time, people refused to believe the earth was round, too.

To understand and dispel many of the skeptics’ theories and arguments, Sloan Science and Film spoke with Richard B. Rood, professor of Atmospheric Sciences at the University of Michigan and a regular contributor to the website, Weather Underground. Most recently, Rood’s post, “Let’s call it: 30 years of above average temperatures means the climate has changed,” looks at data from the past three decades and comes to the conclusion, “The new normal will be systematically rising temperatures.” Below, Rood discusses the connections between carbon dioxide emissions and global warming, the role of the sun, and why the climate change debate is a political argument rather than a knowledge-based argument.

Sloan Science and Film: What do you see as the chief misconceptions about climate change?

Richard Rood: The way I’ve taken to teaching and discussing what we might call the “argument” of those who want to deny or discredit climate change is that reactive denial is an attribute common for virtually every knowledge or science-based set of conditions that imply that society or some entrenched practice needs to change. With climate, if you go back to my colleague Paul Edwards’ book A Vast Machine, you can see that the developing doubt about climate change was pretty solidly set up in the mid-90s, within Congress. What I try to teach my students is that the list of counterfactuals that might challenge climate change is to be expected, and therefore, I ask them to look at the rhetoric or form of argument that people are using. When you hear some claim, such as CO2 is not correlated to temperature change, I work hard for my students to not engage in this counterfactual argument. Because when you say: here’s a fact that questions climate change and here’s why you’re wrong, I think that successfully generates doubt in a policy arena.

SSF: In some ways, I’d like to do just that, and discuss some of the things that the deniers bring up, such as the one you just suggested: doubting the relationship between CO2 and changes in temperature. Can you explain why these two factors are related?

RR: We’ve known for a long time that greenhouse gases are responsible for the earth being at what you’d call a habitability zone. And the two main greenhouse gases are water and CO2. One of the main arguments against CO2 being important to climate change is that it has a smaller impact than water, which is true. And how can something that exists in small amounts matter so much? How CO2 and water influence the energy balance of the earth by absorbing and reemitting infrared radiation—this can be measured and has been measured with some accuracy for some time. We also have evidence of the air trapped in ice cores, and if you look at the ice age-temperate zone oscillations, there is a very strong correlation with CO2 going up and down in concert with the temperature going up and down.

One of the interesting facts about CO2 is that there is a lot of CO2 around and some of it is bound up in the ocean or the trees. And if you look at the amount in the ocean, if water that is rich in CO2 makes it to the surface, or if the ocean’s surface starts to warm, the CO2 in the ocean gets back into the atmosphere, so it’s completely plausible and in fact, quite verifiable, that there are mechanisms in which CO2 increase can precede the temperature increase, and the temperature will respond to that. Temperature increase can also precede CO2 increase, followed by temperature then increasing more because of the CO2. So we can easily establish the relationship between CO2 and temperature. There are many ways that the cycle can get started.

SSF: So the climate change denier would seize on the temperature change scenario that would exist outside of human influence, right?

RR: Yes, that’s another aspect of the denial argument. They will go back and say, look, it’s been changing since before humans. And how do we know it’s humans this time? Or you can say, it’s changed before and the earth did okay. But whenever there have been big changes, something happened to the ocean or plant and animal life, which initiated or was coincident with those changes. So, today, what’s happening is that humans are the activity and a major geological influence on the earth. So it’s humans that are bringing CO2 out of those reservoirs and back into the atmosphere. And human civilization has only emerged in the last 5-10,000 years, when the climate has been conducive to that and sea level rises have been fairly stable. So while the earth has done generically okay in these previous cycles, humans were not around in the same way that we are now, so the disruptions to the human systems that we have today is what drives our interest in this being more than an academically interesting problem.

SSF: What about the argument that we are having the coldest winters on record?

RR: It’s not a uniform warming. The way I usually explain that particular phenomenon is that it still gets cold when the sun goes down over the winter poles. It’s going to get as cold as it’s ever gotten over the dark, polar regions. And it’s very easy to come up with weather patterns that will push that cold air down to regions that may or may not be used to that cold air. If you look at the last two winters in North America, the cold polar air has been pushed towards the eastern side of North America, but what’s going on locally doesn’t represent climate change as a whole. At the same time, you’re seeing warm air pushing up towards Alaska to the point where they had to move the Iditarod Dog Race this year because it was too warm. So climate change, by definition, is looking at an average state, not a local state. Even with the earth warming up, it’s still getting cold over the poles during the winter.

SSF: Is there any data anywhere that suggests that global temperatures, on average, have not increased over the last 100 years?

RR: No, there is no credible data that suggests that global temperatures have not increased. If you look at the observations of surface data—and when we’re talking about global warming, we’re talking about surface temperature, including ocean and ice—all of the evidence is of a warming planet. If you look at just air temperature, which is not really the best individual measure to look at because there’s more variability, you’ll see it jumping up and down. But all of the evidence is that the planet has been warming for the last 150 years. And the last 30 years, I’d argue, is taking place at a rate that is accelerating faster compared with the previous 100 years.

SSF: The hypocrisy of the climate change deniers is very funny, because first, they’ll say, there’s no warming. And then they’ll say, okay, if there’s warming, it’s not bad.

RR: That’s why it’s a political argument as opposed to a knowledge-based argument. Regarding warming trends, another common thing you hear is that the sun is changing. Or you’ll hear that we’re still coming out of the Ice Age. If you go back to questions of the sun changing, the way you rationally argue those problems is you go back to observations and you can measure changes in the sun. And you can, indeed, measure the sun’s relative contribution to the changes that we’re observing on the earth, as a whole. And what you’ll find is that, yes, there are discernible variations in the sun. But when you count up all the contributions of the sun, when you do this budget calculation, it comes out to be smaller than the contributions that come from greenhouse gas increases. So the answer to all those types of challenges to climate change comes in the observations, and if you do those calculations, you can come up with an answer that really has a high certainty: that the cause of current warning is the increase in greenhouse gases, and particularly CO2, and the primary cause of those increases is combustion.

SSF: So why worry?

RR: The changes that we are making right now are unequivocally larger than our societies and cultures have seen since we’ve become a technologically advanced society. The majority of people live in cities, and many of the cities are on the coast, so the sea level rise that we are committed to is going to lead to gigantic disruptions, whether to the people who live there; to energy infrastructure, like in Port Arthur, Texas, or to national security, like in navy yards in Norfolk, Virginia. The changes are so large that you’ll also see tension over natural resources associated with the Arctic. The other thing that’s happening is that the glaciers and ice fields, which regulate water for human consumption and agricultural use, will be changed, such as the seasonable run-off and water availability. And you can keep going down the list, from ecology to agriculture. So casual statements that it will be warmer and there will be more CO2 that is a fertilizer, and that it will be a better world, are not easily substantiated.

SSF: What’s your personal reaction when you hear or read about people denying climate change? Are you angry or frustrated; do you laugh at it?

RR: My reaction to hearing those statements in the press or TV are multifaceted; on one level, I think these things should be expected. I get more frustrated when I see scientific colleagues respond to them in a way that perpetuate the arguments rather than trying to frame the conservation in larger, more productive contexts. And sometimes, I just have to turn off the radio, so to speak.