The following letter from Carl Wunsch is intended to clarify his views on global warming in general, and the The Great Global Warming Swindle which misrepresented them.

Partial Response to the London Channel 4 Film “The Global Warming Swindle”

Carl Wunsch 11 March 2007

I believe that climate change is real, a major threat, and almost surely has a major human-induced component. But I have tried to stay out of the `climate wars’ because all nuance tends to be lost, and the distinction between what we know firmly, as scientists, and what we suspect is happening, is so difficult to maintain in the presence of rhetorical excess. In the long run, our credibility as scientists rests on being very careful of, and protective of, our authority and expertise.



The science of climate change remains incomplete. Some elements are so firmly based on well-understood principles, or for which the observational record is so clear, that most scientists would agree that they are almost surely true (adding CO2 to the atmosphere is dangerous; sea level will continue to rise,…). Other elements remain more uncertain, but we as scientists in our roles as informed citizens believe society should be deeply concerned about their possibility: failure of US midwestern precipitation in 100 years in a mega-drought; melting of a large part of the Greenland ice sheet, among many other examples.

I am on record in a number of places complaining about the over-dramatization and unwarranted extrapolation of scientific facts. Thus the notion that the Gulf Stream would or could “shut off” or that with global warming Britain would go into a “new ice age” are either scientifically impossible or so unlikely as to threaten our credibility as a scientific discipline if we proclaim their reality [i.e. see this previous RC post]. They also are huge distractions from more immediate and realistic threats. I’ve paid more attention to the extreme claims in the literature warning of coming catastrophe, both because I regard the scientists there as more serious, and because I am very sympathetic to the goals of my colleagues who sometimes seem, however, to be confusing their specific scientific knowledge with their worries about the future.

When approached by WAGTV, on behalf of Channel 4, known to me as one of the main UK independent broadcasters, I was led to believe that I would be given an opportunity to explain why I, like some others, find the statements at both extremes of the global change debate distasteful. I am, after all a teacher, and this seemed like a good opportunity to explain why, for example, I thought more attention should be paid to sea level rise, which is ongoing and unstoppable and carries a real threat of acceleration, than to the unsupportable claims that the ocean circulation was undergoing shutdown (Nature, December 2005).

I wanted to explain why observing the ocean was so difficult, and why it is so tricky to predict with any degree of confidence such important climate elements as its heat and carbon storage and transports in 10 or 100 years. I am distrustful of prediction scenarios for details of the ocean circulation that rely on extremely complicated coupled models that run out for decades to thousands of years. The science is not sufficiently mature to say which of the many complex elements of such forecasts are skillful. Nonetheless, and contrary to the impression given in the film, I firmly believe there is a great deal to be learned from models. With effort, all of this is explicable in terms the public can understand.

In the part of the “Swindle” film where I am describing the fact that the ocean tends to expel carbon dioxide where it is warm, and to absorb it where it is cold, my intent was to explain that warming the ocean could be dangerous—because it is such a gigantic reservoir of carbon. By its placement in the film, it appears that I am saying that since carbon dioxide exists in the ocean in such large quantities, human influence must not be very important — diametrically opposite to the point I was making — which is that global warming is both real and threatening in many different ways, some unexpected.

Many of us feel an obligation to talk to the media—it’s part of our role as scientists, citizens, and educators. The subjects are complicated, and it is easy to be misquoted or quoted out context. My experience in the past is that these things do happen, but usually inadvertently — most reporters really do want to get it right.

Channel 4 now says they were making a film in a series of “polemics”. There is nothing in the communication we had (much of it on the telephone or with the film crew on the day they were in Boston) that suggested they were making a film that was one-sided, anti-educational, and misleading. I took them at face value—clearly a great error. I knew I had no control over the actual content, but it never occurred to me that I was dealing with people who already had a reputation for distortion and exaggeration.

The letter I sent them as soon as I heard about the actual program is below. [available here]

As a society, we need to take out insurance against catastrophe in the same way we take out homeowner’s protection against fire. I buy fire insurance, but I also take the precaution of having the wiring in the house checked, keeping the heating system up to date, etc., all the while hoping that I won’t need the insurance. Will any of these precautions work? Unexpected things still happen (lightning strike? plumber’s torch igniting the woodwork?). How large a fire insurance premium is it worth paying? How much is it worth paying for rewiring the house? $10,000 but perhaps not $100,000? There are no simple answers even at this mundane level.

How much is it worth to society to restrain CO2 emissions — will that guarantee protection against global warming? Is it sensible to subsidize insurance for people who wish to build in regions strongly susceptible to coastal flooding? These and others are truly complicated questions where often the science is not mature enough give definitive answers, much as we would like to be able to provide them. Scientifically, we can recognize the reality of the threat, and much of what society needs to insure against. Statements of concern do not need to imply that we have all the answers. Channel 4 had an opportunity to elucidate some of this. The outcome is sad.