I believe that the increase of carbon dioxide is not a cause for alarm and, in fact, will be good for mankind. Before I explain, let me state clearly where I probably agree with other writers on the climate issue. We have been in a period of global warming over the past 200 years, but there have been several periods, like the last ten years, when the warming has nearly ceased, and there have even been periods of moderate cooling, as from 1940 to 1970. Atmospheric concentrations of carbon dioxide (CO2) have increased from about 280 to 380 parts per million (ppm) over the past century. The combustion of fossil fuels—coal, oil and natural gas—has contributed to the increase of CO2 in the atmosphere. And finally, increasing concentrations of CO2 in the atmosphere will cause the earth’s surface to warm. The key question is: will the net effect of the warming, and any other effects of the CO2, be good or bad for humanity?

I predict that future historians will look back on this period much as we now view the period just before the passage of the 18th Amendment to the US Constitution to prohibit “the manufacturing, sale or transportation of intoxicating liquors.” At the time, the 18th amendment seemed to be exactly the right thing to do—who wanted to be in league with demon rum? More than half the states enacted prohibition laws before the 18th amendment was ratified. Only one state, Rhode Island, voted against the 18th amendment. There were many thoughtful people, including a majority of Rhode Islanders, who thought that prohibition might do more harm than good. But they were completely outmatched by the temperance movement. Then as now, deeply sincere people thought they were saving humanity, be it from the evils of alcohol or CO2. Prohibition was a mistake, and our country has probably still not fully recovered from the damage it did. Institutions like organized crime got their start in that era. Current proposals to curb carbon emissions could lead to different but no less serious negative effects.

But what about the frightening consequences of increasing levels of CO2 that we keep hearing about? In a word, they are wildly exaggerated, just as the purported benefits of prohibition were wildly exaggerated. Let me turn now to the science and try to explain why I and many scientists like me are not alarmed by increasing levels of CO2.

The earth’s climate really is strongly affected by the greenhouse effect, although the physics is not the same as that which makes real, glassed-in greenhouses work. Without greenhouse warming, the earth would be much too cold to sustain its current abundance of life. However, the largest single contributor to the greenhouse effect is water vapor and clouds, which studies indicate are responsible for between 66% and 85% of the total effect. Carbon dioxide contributes a smaller amount, no more than 25%. There is little argument in the scientific community that a direct effect of doubling the CO2 concentration would produce a small increase in the earth’s temperature—on the order of one degree. Additional increments of CO2 will cause relatively less direct warming because we already have so much CO2 in the atmosphere that it has blocked most of the infrared radiation that it can. It is like putting an additional ski hat on your head when you already have a nice warm one below it, but you are only wearing a windbreaker. To really get warmer, you need to add a warmer jacket. The UN Intergovernmental Panel on Climate Change (IPCC) thinks that this extra jacket is water vapor and clouds.

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Since most of the greenhouse effect for the earth is due to water vapor and clouds, added CO2 must substantially increase water’s contribution to lead to the frightening scenarios that are bandied about. The buzz word here is that there is “positive feedback.” Some recent observations, however, have indicated that this positive feedback mechanism may not be as large as previously expected. The evidence here comes from satellite measurements of infrared radiation escaping from the earth into outer space, from measurements of sunlight reflected from clouds and from measurements of the temperature the earth’s surface or of the troposphere, the roughly 10 km thick layer of the atmosphere above the earth’s surface that is filled with churning air and clouds, heated from below at the earth’s surface, and cooled at the top by radiation into space.

But the climate is warming and CO2 is increasing. Doesn’t this prove that CO2 is causing global warming through the greenhouse effect? There have been similar warmings several times in the 10,000 years since the end of the last ice age. These earlier warmings clearly had nothing to do with the combustion of fossil fuels. The current warming may very well also be due mostly to natural causes, not to industrial activity.

There is much talk about the “pollutant CO2,” or about “poisoning the atmosphere” with CO2. We are told that we need to minimize our “carbon footprint.” But CO2 is not a pollutant and it is not a poison and we should not corrupt the English language by depriving “pollutant” and “poison” of their original meaning. Our exhaled breath contains about 4% CO2. That is 40,000 parts per million, or about 100 times the current atmospheric concentration. CO2 is absolutely essential for life on earth. Commercial greenhouse operators often use CO2 as a fertilizer to improve the health and growth rate of their plants. We try to keep CO2 levels in our US Navy submarines no higher than 8,000 parts per million, about 20 times current atmospheric levels. Few adverse effects are observed at even higher levels (while too much C02 is poisonous for animals, including humans, no one suggests that anthropogenic emissions could ever cause atmospheric levels to reach anywhere near the level of C02 that is directly toxic).

We are all aware that “the green revolution” has increased crop yields around the world. Part of this development is due to improved crop varieties and better use of mineral fertilizers and herbicides. But no small part of the yield improvement may have come from increased atmospheric levels of CO2. Plants photosynthesize more carbohydrates when they have more CO2. Plants are also more drought-tolerant with more CO2, because they need not “inhale” as much air to get the CO2 needed for photosynthesis. At the same time, the plants need not “exhale” as much water vapor when they are using air enriched in CO2. Plants decrease the number of stomata or air pores on their leaf surfaces in response to increasing atmospheric levels of CO2. They are adapted to changing CO2 levels and they prefer higher levels than those we have at present. If we really were to decrease our current level of CO2 of around 400 ppm to the 270 ppm that prevailed a few hundred years ago, we could lose some of the benefits of the green revolution. Crop yields may well continue to increase as CO2 levels go up, since we are far from the optimum levels for plant growth. Commercial greenhouse operators are advised to add enough CO2 to maintain about 1000 ppm around their plants. One possible conclusion that can be drawn from a recent study by Dr. Robert Mendelsohn at Yale University is that moderate warming may be an overall benefit to mankind in part because it could lead to higher agricultural yields.

In Voltaire’s Candide, Dr. Pangloss repeatedly assured young Candide that they were living in “the best of all possible worlds,” presumably also with the best of all CO2 concentrations. That we are (or were) living at the best of all CO2 concentrations seems to be a tacit assumption of the IPCC executive summaries for policy makers. Enormous effort and imagination have gone into showing that increasing concentrations of CO2 will be catastrophic. Alarmists have said that cities will be flooded by sea-level rises that are ten or more times bigger than even IPCC predicts, there will be mass extinctions of species, billions of people will die, tipping points will render the planet a desert. A few months ago I read that global warming will soon bring on a devastating epidemic of kidney stones. If you write down all the ills attributed to global warming you fill up a very thick book.

It is frequently asserted that there is a consensus behind the idea that there is an impending disaster from climate change, and that it may already be too late to avert this catastrophe, even if we stop burning fossil fuels now. We are told that only a few flat-earthers still have any doubt about the calamitous effects of continued CO2 emissions. There are a number of answers to this assertion. Indeed, we are not facing a crisis unless we create one for ourselves.

The sea level is indeed rising, just as it has for the past 20,000 years since the end of the last ice age. Fairly accurate measurements of sea level have been available since about 1800. These measurements show no evidence of any acceleration—in spite of the increased levels of CO2. The naturally rising sea level can be a serious local issue for heavily-populated, low-lying areas like New Orleans, where land subsidence compounds the problem. But to think that merely limiting CO2 emissions will stop sea level rise is a dangerous illusion. It is also possible that the warming seas around Antarctica will cause more snowfall over the continent and will counteract the sea-level rise. Indeed, recent observations suggest that exactly this effect is operative in certain parts of Antarctica where ice coverage has been increasing. In any case, the rising sea level is a problem that needs quick local action for locations like New Orleans rather than slow action globally.

It is regrettable that the climate-change issue has become confused with immediate and serious problems like secure energy supplies, protecting our environment, and figuring out where future generations will get energy supplies or chemical feedstocks after we have burned all the fossil fuel we can find. We should not confuse these laudable goals with hysterics about carbon footprints. For example, when weighing pluses and minuses of the continued or increased use of coal, our worry should not be increased atmospheric CO2, which may well be good for mankind. We should focus on real issues like damage to the land and waterways by strip mining, inadequate remediation, hazards to miners, the release of real pollutants and poisons like mercury, other heavy metals, organic carcinogens, etc.  Much of the potential harm from coal mining can be eliminated, for example, by like strict requirements that strip-mined land be restored to a condition that is as least as good, and preferably better than when the mining began. Life is about making decisions and decisions are about trade-offs. We can choose to promote investment in technology that addresses real problems and scientific research that will let us cope with real problems more efficiently. Or we can act on unreasonable fears and suppress energy use, economic growth and the benefits that come from the creation of national wealth.

This paper was adapted from testimony given before the U.S. Senate Environment and Public Works Committee on February 25, 2009.