Doug Keenan suggests that I publish the whole of his correspondence with Prof Denning. Given that much of this has appeared on Yale Climate Forum already, I guess this is OK.

Dr. Denning,

The Yale Climate Forum quotes you as saying “Almost everyone that dismisses climate change as a problem does it for ideological or political reasons, not for scientific reasons”. You appear to have done what Richard Betts warns against in the Forum article: gotten your “impression of the other group second-hand”. As Betts notes, that “leads to further misunderstandings and increased bitterness”.
 
I ask you to read the reasons that skeptics have given. Last year, I published an op-ed piece in the Wall Street Journal, which was subheaded thus: “What is arguably the most important reason to doubt global warming can be explained in plain English”. If you have a rebuttal to that piece, I would be much interested is seeing it.

Dear Dr. Keenan,
 
Thank you for your note.

Actually I have personally spoken with literally thousands of people who don't "believe" in climate change. I meet regularly with such groups: at the Heartland Institute's annual conference; at Colorado Christian University; and the Western Cattlemen's Association; and at public presentations across the US. Nearly all of them have been opposed almost entirely on ideological rather than scientific grounds. This is not hearsay -- it's simply been my personal experience.
 
 I respect ideology and belief. I understand that people are opposed to big government and inefficient political intrusion in the free market. I am very sympathetic to these beliefs, and have found that mutual respect can help people to find common ground on climate and other issues.

I do recognize that there are people, yourself included, that have specific scientific objections to scientific results on climate. However, I find each person's objection to be rather idiosyncratic. You complain about autoregression in timeseries, for example. Others have similarly narrow objections based on temperature trends of Saturn's moons, Milankovitch cycles, numerical approximations, cloud parameterizations, urban heat islands, etc. The list seems endless. But there is no unified "contrarian" critique of mainstream science; merely a thousand tiny details without a theme other than anger.
 
The criticism you level in your WSJ opinion piece is a great example of my point. You pick a tiny issue (autoregression in timeseries analysis), and analyze it in detail, giving the false impression that this is somehow an important objection to mainstream science. The false premise is that concerns about future warming are based on extrapolation of recent trends. This is certainly not the case, as the mainstream science is based on laboratory spectroscopy of CO2 gas that is backed up by 150 years of experimental data!
 
Climate scientists are concerned about future warming not because it's been getting warmer lately, but because we know that (a) burning fossil fuel emits CO2; (b) CO2 molecules emit heat; and (c) heat warms things up. We can confidently predict a warmer climate under elevated CO2 for precisely the same reason we can predict that Miami will be warmer than Minneapolis this year.
 
I urge you to spend some time really listening to scientists, as I've spent countless hours listening to contrarians. It's been a wonderful experience for me, and I'm sure you could broaden your horizons as well!
 
Sincerely,
Scott Denning, Ph.D.

Dr. Denning,
 
My op-ed piece explains that a whole chapter of the most-recent IPCC report is unfounded: the chapter, moreover, which claims global temperatures have been significantly increasing. Your message asserts that this is a "tiny issue". Clearly, the assertion is untrue and you know it to be untrue.

Your message additionally asserts that because "CO2 molecules emit heat" global warming must be substantial. By such reasoning, a person who put their feet in a bucket of hot water would have their hand temperature increase. Earth's climate system has mechanisms for dealing with heat, and CO2 concentrations have been higher in the past. You know all this.

Etc.

I previously wondered if you were dishonest or just confused. I no longer wonder about that: your reply is substantively dishonest.
 
Douglas J. Keenan

Dear Mr. Keenan,

Thanks for your reply. If you wish to be taken seriously, please keep your correspondence respectful. I don't claim to be infallible, but I assure you I am not dishonest. You specifically asked me to rebut your opinion piece in the WSJ, and I have taken your request at face value. I am more than willing to listen and discuss, but I am not interested in trading insults.

Scientific concern about climate change arising from CO2 emitted by burning fossil fuel predates the IPCC by well over 100 years. The concern is based on very simple physics, not on rising temperatures or timeseries analysis.

Everything in the universe emits heat (yes, even ice water!). At a given temperature, CO2 molecules emit much more than the oxygen and nitrogen molecules that make up 99% of the atmosphere. This effect has been known quantitatively since 1863. The emissions have been independently measured wavelength-by-wavelength thousands of times in hundreds of spectroscopy laboratories around the world, with increasing precision and cannot reasonably be disputed.

The Earth's surface is warmed by the Sun during the day. But at night there is no sunshine, yet thankfully we do not freeze to death each night. That's because the sky also emits heat that is absorbed by the Earth's surface. We can easily measure the heat received from each source (the sun vs the rest of the sky). The measurements show that every square meter of the Earth's surface receives about twice as much heat from the warm sky (333 Watts) as from the Sun (161 Watts). Again, these are simple measurements that have been repeated all over the world. Without this extra heat emitted by CO2 and H2O molecules in the sky, the oceans would long ago have frozen solid, to the bottom.

It is perfectly reasonable to ask how sensitive (in degrees Celsius) the Earth's climate is to changes in heating (in Watts). But it seems disingenuous to assert that heat doesn't change temperature. Everyday experience with teapots, hands, and feet refute such a claim.

Doubling the number of heat-emitting CO2 molecules adds 4 Watts per square meter to the Earth's surface. Assuming that China and India emerge as industrial economies in the 21st Century, and continue to drive these enormous economies with coal, the number of CO2 molecules in the warm sky will not merely double, but quadruple relative to 20th Century values. In that case there will be 8 extra Watts of heat provided to each square meter of the Earth's surface, 24 hours per day, 365 days a year, for many centuries.

By comparison, 18,000 years ago, when ice sheets straddled Europe and North America the Earth's surface received about 7 fewer Watts of heat per square meter. Evidently a few Watts per square meter, applied over time, make a big difference to surface temperatures! The 7 Watts per square meter of post-glacial heating was applied gradually over 100 centuries of melting ice. Yet Plan A is to apply a similar heating in the 21st Century to accommodate the welcome economic transition of the developing world.

Personally, I believe in capitalism, freedom, and the power of market incentives to drive innovation. I'd be interested in your thoughts about how these principles might best be used to provide a decent standard of living for billions of people without dramatic changes to the energy balance of the Earth's surface.

Sincerely,
Scott Denning, Ph.D.

Dr. Denning,

Your message claims that "Doubling the number of heat-emitting CO2 molecules adds 4 Watts per square meter to the Earth's surface". Here is an admittedly rough analogy. If one end of a beam is put in a bucket of hot water, the other end will warm: that is simple physics. A person who puts their feet in a bucket of hot water, however, will not have their hand temperature increase. The reason is that person is a complex system that has mechanisms for dealing with heat ("feedbacks"). Similarly, Earth's climate system has mechanisms to deal with heat. Because of such mechanisms, the simple physics that you describe is misleading.

As an example, it has been proposed that as Earth heats, clouds shift to allow more heat to escape into space; temperatures on Earth's surface are thereby reduced. This is sometimes called the "iris hypothesis", in analogy with how the eye's iris works. The hypothesis exemplifies how it is essential to understand feedback mechanisms dealing with heat.

The iris hypothesis was proposed by Richard Lindzen, in 2001. Note that Lindzen is usually considered to be the world's leading expert on clouds.

Substantial discussion of feedback mechanisms dealing with heat is given in the most-recent (2007) Assessment Report from the IPCC: section 8.6. That section is part of chapter 8, with deals with climate models. The reason that this issue is usually discussed with climate models is that the various mechanisms are numerous, nonlinear, interacting, etc.: climate models are often considered the best to deal with such complexity. The IPCC section concludes that "it is not yet possible to assess which of the model estimates of cloud feedback is the most reliable", which alone counters your claim.

Discussions pertaining to feedback mechanisms have of course continued since the publication of the IPCC report. I have not followed them though. One paper that I recall is by Lindzen & Choi [2011]. Recently, Davies & Molloy [2012] has been in the news.

We now have two options.

1. You are truly ignorant of all of the above.

2. You are aware of at least some of the above and your message is dishonest.

Your web page says that you (a) have a Ph.D. in atmospheric science, (b) have been working in this area of climatology for many years, and (c) have been an editor of the world's top journal for climatological research, Journal of Climate; hence option 1 is not credible. I conclude that you are dishonest. This is in addition to the evidence presented in my previous message.

I would not usually reply to such dishonesty, but the e-mail from Bud Ward indicated that an elaboration of my previous message might be appropriate.