First Things 
May 23, 2011
The object of the Author in the following pages has been to collect the most remarkable instances of those moral epidemics which have been excited, sometimes by one cause and sometimes by another, and to show how easily the masses have been led astray, and how imitative and gregarious men are, even in their infatuations and crimes,” wrote Charles Mackay in the preface to the first edition of hisExtraordinary Popular Delusions and the Madness of Crowds. I want to discuss a contemporary moral epidemic: the notion that increasing atmospheric concentrations of greenhouse gases, notably carbon dioxide, will have disastrous consequences for mankind and for the planet. The “climate crusade” is one characterized by true believers, opportunists, cynics, money-hungry governments, manipulators of various types—even children’s crusades—all based on contested science and dubious claims.
I am a strong supporter of a clean environment. We need to be vigilant to keep our land, air, and waters free of real pollution, particulates, heavy metals, and pathogens, but carbon dioxide (CO2 ) is not one of these pollutants. Carbon is the stuff of life. Our bodies are made of carbon. A normal human exhales around 1 kg of CO2 (the simplest chemically stable molecule of carbon in the earth’s atmosphere) per day. Before the industrial period, the concentration of CO2 in the atmosphere was 270 ppm. At the present time, the concentration is about 390 ppm, 0.039 percent of all atmospheric molecules and less than 1 percent of that in our breath. About fifty million years ago, a brief moment in the long history of life on earth, geological evidence indicates, CO2 levels were several thousand ppm, much higher than now. And life flourished abundantly.
Now the Environmental Protection Agency wants to regulate atmospheric CO2 as a “pollutant.” According to my Webster’s New Collegiate Dictionary, to pollute is “to make or render unclean, to defile, to desecrate, to profane.” By breathing are we rendering the air unclean, defiling or desecrating it? Efforts are underway to remedy the old-fashioned, restrictive definition of pollution. The current Wikipedia entry on air pollution, for example, now asserts that pollution includes: “carbon dioxide (CO2)—a colorless, odorless, non-toxic greenhouse gas associated with ocean acidification, emitted from sources such as combustion, cement production, and respiration.”
As far as green plants are concerned, CO2 is not a pollutant, but part of their daily bread—like water, sunlight, nitrogen, and other essential elements. Most green plants evolved at CO2 levels of several thousand ppm, many times higher than now. Plants grow better and have better flowers and fruit at higher levels. Commercial greenhouse operators recognize this when they artificially increase the concentrations inside their greenhouses to over 1000 ppm.
Wallis Simpson, the woman for whom King Edward VIII renounced the British throne, supposedly said, “A woman can’t be too rich or too thin.” But in reality, you can get too much or too little of a good thing. Whether we should be glad or worried about increasing levels of CO2 depends on quantitative numbers, not just qualitative considerations.
How close is the current atmosphere to the upper or lower limit for CO2? Did we have just the right concentration at the preindustrial level of 270 ppm? Reading breathless media reports about CO2 “pollution” and about minimizing our carbon footprints, one might think that the earth cannot have too little CO2, as Simpson thought one couldn’t be too thin—a view which was also overstated, as we have seen from the sad effects of anorexia in so many young women. Various geo-engineering schemes are being discussed for scrubbing CO2 from the air and cleansing the atmosphere of the “pollutant.” There is no lower limit for human beings, but there is for human life. We would be perfectly healthy in a world with little or no atmospheric CO2—except that we would have nothing to eat and a few other minor inconveniences, because most plants stop growing if the levels drop much below 150 ppm. If we want to continue to be fed and clothed by the products of green plants, we can have too little CO2.
The minimum acceptable value for plants is not that much below the 270 ppm preindustrial value. It is possible that this is not enough, that we are better off with our current level, and would be better off with more still. There is evidence that California orange groves are about 30 percent more productive today than they were 150 years ago because of the increase of atmospheric CO2.
Although human beings and many other animals would do well with no CO2 at all in the air, there is an upper limit that we can tolerate. Inhaling air with a concentration of a few percent, similar to the concentration of the air we exhale, hinders the diffusional exchange of CO2 between the blood and gas in the lung. Both the United States Navy (for submariners) and nasa (for astronauts) have performed extensive studies of human tolerance to CO2. As a result of these studies, the Navy recommends an upper limit of about 8000 ppm for cruises of ninety days, andnasa recommends an upper limit of 5000 ppm for missions of one thousand days, both assuming a total pressure of one atmosphere. Higher levels are acceptable for missions of only a few days.
We conclude that atmospheric CO2 levels should be above 150 ppm to avoid harming green plants and below about 5000 ppm to avoid harming people. That is a very wide range, and our atmosphere is much closer to the lower end than to the upper end. The current rate of burning fossil fuels adds about 2 ppm per year to the atmosphere, so that getting from the current level to 1000 ppm would take about 300 years—and 1000 ppm is still less than what most plants would prefer, and much less than either the nasa or the Navy limit for human beings.