Almost 20 years ago, Harold Lewis, a respected physicist who had advised the government and the Pentagon on matters ranging from nuclear winter to missile defense, included his assessment of climate change from the buildup of human-generated greenhouse gases in a book on technological risk:

All models agree that the net effect will be a general and global warming of the earth; they only disagree about how much. None suggest that it will be a minor effect, to be ignored while we go about our business. [ Read more.]

A couple of pages later, he laid out the implications of warming and the need for “global cooperation and sacrifice now, to avert something far in the future.” He noted that this was unlikely, given human nature, but said, “one can only hope.” Here’s the relevant section:

What a difference a couple of decades can make. One week ago Lewis was vaulted to celebrity status by conservative and contrarian Web sites and commentators when he disseminated his letter of resignation from the 48,000-member American Physical Society over its support for what he called “the global warming scam, with the (literally) trillions of dollars driving it, that has corrupted so many scientists, and has carried APS before it like a rogue wave.”

Lewis’s letter contained a long list of complaints, ranging from the group’s lack of a response to his efforts to convene a committee to assess evidence for a human link to climate change to its defense of choosing the word “incontrovertible” to describe the evidence for global warming in its statement on climate science and policies in 2007. (The society added a substantial sentence-by-sentence deconstruction of its statement earlier this year, but stuck with the original language.) He concluded that, in his view, global warming was “the greatest and most successful pseudoscientific fraud I have seen in my long life as a physicist.”

Below you can read parts of an e-mail exchange I had this week with Lewis, aiming to clarify how he came to this conclusion. I only stumbled on the excerpts from his 1992 book Thursday night, after our initial discussions. I’ve sent him a follow-on query about how his conclusions then relate to his views now and will provide an update when he responds.

For its part, the American Physical Society issued a statement on Tuesday denying any financial interest in forming its stance on global warming science and policy and defending its statements on the issue. It also defended the preponderant scientific view of basic climate conclusions, saying:

In light of the significant settled aspects of the science, APS totally rejects Dr. Lewis’ claim that global warming is a “scam” and a “pseudoscientific fraud.”

Here are relevant excerpts from my exchange with Lewis (with some e-mail shorthand adjusted). Revkin:

I’d greatly appreciate a few minutes of your time to try to get some clarification of where you see the fraud ending and the legitimate science beginning. Too often, the vague concept of human-driven global warming is dealt with as a single entity when in fact it’s a host of questions: – How much can humans warm the planet?

– How much HAVE humans warmed the planet (so far; the attribution question)?

– How much warming is too much?

– What’s the best way to limit climate-related risks as human numbers and appetites crest in the next few decades? Each question has its own issues and evidence, to my mind….

Lewis:

OK, as a first step, fraud is a contagious disease. Bernie Madoff committed fraud, pure and simple, but the people who profited from it covered the spectrum. Undoubtedly some were completely unaware, and there was every gradation…. The important thing for me is the suppression of open debate, which is the conventional way to identify fraud. Your specific questions. No one knows how much humans can (your word) warm the planet — the science is complicated. It might be a degree or two (Celsius) per century, but anyone who says he knows is committing fraud. How much HAVE (your capitalization) people warmed the planet, again no one knows. Within what is actually known (not computer modeled) it could be zero. I believe I was chairing JASON in the early 1970s when Gordon MacDonald ran our first computer modeling on the subject, and the results were not all that different from what people get now using the same methods. But there were no data then on attribution, and there are no data now. It’s not a coffee klatch subject. How much warming is too much? There is no universal metric for such matters. I used to think that Phoenix was unbearably hot, but Indians lived there. I’ve spent lots of time in New Mexico (Los Alamos), where 7,000 feet makes high temperatures a pleasure. Humans adapt. The fact that we can adapt intelligently is what distinguishes us from others of our fellow animals. Of course most conceivable adaptations require energy (compare Phoenix), so the stupidest thing we can do is deprive ourselves of real energy to protect against conjectured warming. What’s the best way to limit climate-related risks as human numbers crest… First use real science to identify and quantify the threats, then I’ll propose responses. First things first. I remember the motto that made the rounds at the first Sputnik in the late 1950s: When in trouble or in doubt, run in circles; scream and shout. Not a good answer to any human problem.

Revkin:

– One point to ponder in your response to the greenhouse sensitivity question is that your conclusion about fraud would apply to anyone who says he knows the warming would be a minor inconvenience, along with anyone stating firmly that a meltdown is nigh, right? Would you agree on that? In other words, anyone concluding with high confidence that humans cannot substantially heat the planet — given the enduring questions — is not being honest, right?

Lewis:

[A]nyone who claims to be able to predict the climate well enough to guide public policy is committing a fraud. HOWEVER there are harmless frauds and harmful ones, and i have far less animus toward perpetrators of the former. That’s as a citizen; as a physicist, no fraud is acceptable. So even though cold fusion hurt no one, it was a sin. The consequences matter.

Again, I’ll update this post when Lewis offers an explanation of why his views on global warming research and risk have so starkly changed. In the meantime, I asked another student of technological risk, David Ropeik, to have a look at Lewis’s letter. Here’s his analysis:

I just read Dr. Lewis’ angry letter of resignation from the APS. It puts him at an extreme on the spectrum of debate over climate change in both tone and substance. So I guess the old reporter instincts in me would be cautious about anything he’d have to say, as would be the case with any extreme advocate on any side of any issue. Much more to the point, however, it is not surprising that, as a physicist, he not only laments that people are too worried about some technological risks, but he is frustrated and condescending toward what he describes as people’s irrationality regarding these issues. What strikes me as irrational is that an intelligent person like Dr. Lewis, who has devoted his professional life to science, would either pay no heed to, or dismiss, the mountains of scientific evidence, from neuroscience and psychology and economics and sociology, that demonstrates beyond any serious question that the way we perceive risk is affective… Our fears are a combination of the facts and how those facts feel. Our brains are hard wired to do it this way. It seems Dr. Lewis is demonstrating the very phenomenon he laments, letting his affect and worldviews interfere with taking all the reliable evidence into account in order to make a truly informed and fair judgment.

I share Ropeik’s view.