Issue Date: December 21, 2009
Carbon Dioxide And Global Warming Redux
In his letter to the editor, Jihong Cole-Dai points out that "many chemists are skeptical about the science of global warming" (C&EN, Aug. 24, page 5). This accusation is just unsound; most chemists believe in man-made global warming.
Cole-Dai addresses the following question: "How many kilocalories of infrared energy can a ton of carbon dioxide adsorb?" and his answer is "an unlimited amount." His reasoning is that excited CO2 molecules are quenched by the other atmospheric molecules and quickly return to the ground state. This statement needs several remarks:
• Electromagnetic energy is absorbed and not adsorbed (see the International Union of Pure & Applied Chemistry's "Compendium of Chemical Terminology"—the Gold Book).
• Each metric ton can, indeed, absorb an unlimited amount of energy—if I wait an unlimited amount of time. However, the absorbed energy per time unit is the important value. Even if the vibrationally excited state of a molecule is extremely short lived, it has a defined lifetime and, therefore, there will be saturation of ground-state absorption (all molecules are excited) if the intensity of irradiation is high enough.
• However, even if saturation of ground-state absorption occurs, an increase of atmospheric CO2 will increase global warming because a vibrationally excited CO2 absorbs another quantum of infrared radiation to go to a higher excited state. And if the number of CO2 molecules in the atmosphere is doubled, they need (in first approximation) to absorb about twice the amount of IR radiation to achieve saturation.
Therefore, saturation is not a reason anyone should discount man-made global warming. I am not an atmospheric chemist and do not have the details, but the energy CO2 can absorb per time unit is definitely not unlimited.
The answer to the "legitimate" question Cole-Dai poses as to why CO2 can cause global warming when it is a minor component of the atmosphere and its absorption in the IR region is weak is because the absorption is weak and the concentration is low.
Consider the opposite. According to the Beer-Lambert law, a high absorption coefficient and a high concentration do lead to a high absorbance, just say 3. At that absorbance, 99.9% of all IR photons are absorbed, and even a huge increase of atmospheric CO2 will have only a minor effect on absorbed energy. However, if you consider a low absorbance (low CO2 concentration, low absorption coefficient) of say 0.01, a doubling of atmospheric CO2 will lead to an absorbance of 0.02. If you compute from this value the number of absorbed photons by constant irradiation, you will find a twofold increase, which is in agreement with the fact that the Beer-Lambert law can be approximated as a linear function at low absorbances.
Therefore, CO2 can act efficiently only because of its low concentration and low absorption coefficient. Again, I am not an atmospheric chemist, and I do not know any numbers, but this is basic physical chemistry.
Can you stand one more letter regarding your stance on the global-warming issue? I am an emeritus ACS member and have been for a number of years. That does not make me any more qualified on the subject of global warming, but it does mean that I probably have more historical perspective to offer.
Specifically, I well remember back in the early 1960s when the editor of C&EN regularly authored editorials that vehemently denounced Rachel Carson and the cause she espoused. The essence of those editorials was that she was a crackpot environmentalist who was attacking the very foundations of chemistry and modern science.
According to C&EN, Carson's position that DDT was in any way harmful was absurd. After all, during World War II, DDT was as valuable to victory as penicillin. And postwar, many communities used DDT freely in aerial spraying programs to control mosquitoes.
But Carson, the beleaguered author of "Silent Spring," ultimately prevailed. She convinced the nation that DDT was not the benign substance that C&EN and the rest of us believed. As a result, it was banned in 1972.
Personally, I accept that global warming is taking place; however, like many others, I am not yet fully convinced that is primarily due to human activity rather than a periodic swing of natural occurrence. Hence, I believe that "the jury is still out" on this issue. Moreover, I would hope that ACS and C&EN have learned from their past mistake on DDT. No one likes to eat crow twice!
Edward G. Feldmann
Like Rudy Baum, I am also amazed at the anger in the letters concerning climate change (C&EN, July 27, page 5). However, we must realize that this has more to do with the extreme right-wing politics that is becoming pervasive in a minority of the population, including scientific organizations. The writers really are not looking at the science or are even interested in it.
People who are climate-change deniers, in the teeth of overwhelming evidence, are really responding to the policy change implications. If they accept the evidence, they then have to admit that very major and rapid changes must be accomplished both in our civilization and our very way of life. That is the heart of the issue. No amount of evidence will ever convince them.
Now that it has been shown that the so-called "respectable" scientists who have been leading the "global warming" charade have been purposely hiding data, "fudging" other data, and defining any research that shows the cooling trend of the past decade as "not peer-reviewed," perhaps it might behoove the leaders of ACS to rethink the "official policy" supporting the contention that there is an anthropogenic "crisis" looming, due to CO2 emissions. Hopefully, there is enough time to make the truth widespread before the U.S. gets caught up in the "cap and trade" fiasco. Now there is a crisis waiting to happen.
George St. George
So I am a climate-change denier! Although this places me in the august company of Sen. James Inhofe (R-Okla.), I still resent the not-so-subtle and undoubtedly intentional reference to the lunatic fringe of Holocaust deniers. C&EN goes beyond the bounds of decency here. We can tolerate the expression of controversial views in our magazine, may even welcome them, but do demand respect for opposing views.
The likely truth is that Copenhagen is unlikely to resolve climate change because that may be outside the reach of mankind. It is preposterous, and the height of arrogance, to think that we know enough of what governs the climate, let alone its effect on Earth's habitability.
Who was the famous ball player who said: "It ain't what we don't know that will do us in, it's what we know that ain't so"?
A. E. Lippman
- Chemical & Engineering News
- ISSN 0009-2347
- Copyright © American Chemical Society