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Re: [Phys-l] Climate skeptic convinced by data. Was: Re: Mike Mann _The hockey

I haven't heard anything approaching a compelling response either. But there have been some fascinating incorrect and partially correct responses, and these can at least help us better understand the physics.

The CO2 spike is in a way quite remarkable. If you had told me that humans are adding so many gazillion tons of CO2 to the atmosphere every year and asked me to guess what fraction of that added CO2 stays in the atmosphere (rather than being absorbed by plants or water), I would have guessed that the fraction is either close to zero or close to 100%. That is, either the absorption mechanisms can easily keep up with the emissions, or they can't keep up at all. But in fact, the fraction is close to 50%. I find this a remarkable coincidence and although I'm sure the experts understand the reasons in detail, I'm not aware of any simple explanation.

There actually are some climate skeptics who deny the basic physics of the greenhouse effect. Sadly, some of them are professional physicists, and have even gotten a paper published in a peer-reviewed journal. Just Google "Gerlich and Tscheuschner" if you're not already aware of this embarrassing incident. Be sure to read Arthur Smith's devastating rebuttal.

I think you need more than "common sense" to translate the known CO2 increase into a quantitative predicted temperature increase. An extremely naive argument would say that if CO2 is responsible for a third of the current 33C greenhouse effect, then doubling CO2 would increase the average temperature by another 11C. A more sophisticated argument would say that doubling CO2 won't have any effect at all, because the CO2 absorption band is already "saturated" by existing CO2 concentrations and so adding more CO2 doesn't cause any additional absorption at these wavelengths. The correct analysis acknowledges that the middle of the absorption band is saturated but then goes on to consider the "shoulders" of the absorption band as well as energy transport processes in the atmosphere. The resulting prediction, without feedbacks, is a temperature increase on the order of only about 1C. That's for a doubling of pre-industrial CO2 levels, so I don't think it's correct that "simple" models predict a "few-degree" increase at current CO2 levels.

The reason why the skeptics can get away with their nonsense is precisely because the effects are small and the correct explanations are complicated. As a physicist, I find this situation extremely frustrating.

Dan


On Feb 20, 2012, at 10:00 AM, phys-l- request@carnot.physics.buffalo.edu wrote:

From: John Mallinckrodt <ajm@csupomona.edu>
Date: February 19, 2012 11:25:12 AM MST
To: Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu>
Subject: Re: [Phys-l] Climate skeptic convinced by data. Was: Re: Mike Mann _The hockey
Reply-To: Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu >


Whenever debates like this get going among people who presumably CAN be persuaded by evidence and rational argument, I like to haul out a simple summary provided by Art Hobson a couple of years ago. I have yet to hear anything approaching a compelling response. Maybe this time will be different.

"The sudden atmospheric CO2 spike during only the past two centuries is unprecedented in at least 800,000 years of alternating ice ages and interglacials. This spike is of undeniably human origin; so far as I know, even climate skeptics agree with this statement. The natural greenhouse effect undeniably warms Earth’s surface by 33 degrees C, and CO2 is known to be the second strongest greenhouse gas, after water vapor. There’s every reason to think that this CO2 spike is responsible for the temperature increase, and indeed nobody has proposed a plausible alternative mechanism. Common sense, simple models, and all of the computer models predict that the CO2 spike should cause a few-degree increase in the greenhouse effect. That’s exactly what’s been happening. Indeed, climate skeptics need to answer the obvious question: Why wouldn’t you expect that high CO2 levels are causing high temperatures?"

--Art Hobson, The Physics Teacher, Vol. 48, pp 502-503, November 2010

John Mallinckrodt
Cal Poly Pomona