All of us, I can say with confidence, are aware of the debates about global warming, at least at the level of political dispute. The present state of the debate seems to be this: Most experts agree that human activities, including the burning of fossil fuels and the deforestation of large areas, are having the effect of raising the world's average temperature, with potentially far-reaching consequences for agriculture, the viability of coastal settlements, and so forth. A relatively small minority of experts disagree. Those who accept the judgment of the majority of experts conclude that the nations of the world should take deliberate and sometimes costly efforts to reduce carbon emissions; those who accept the minority judgment disagree. This then has become a signature left-right debate, with those on the left calling for immediate action and those on the right claiming that such action will have a disastrous effect on the profitability of capital. Everyone engaged in the debate seems to agree that the decision to control carbon emissions should depend on one's evaluation of the claim that carbon emissions are causing global warming. I should like to suggest that this is confused way of thinking. I offer these thoughts in the full acknowledgement that I am a complete tyro when it comes to the relevant science. My knowledge is limited to the reading of a few books [including a bizarre novel by Michael Crichton that is a thinly disguised polemic against the defenders of the global warming thesis]
There is no scientific disagreement about the well-established fact that the average temperature of the earth has varied considerably over the past several billion years. At one point, it appears that for several hundred million years the entire earth was covered with ice [the "snowball earth" thesis], and the Great Lakes, Finger Lakes, and other familiar geological formations are evidence of the periodic advance and retreat of glacial fields. There has even been a period of temperature fluctuation in the relatively recent historical past. Starting the the late 13th century, glaciers advanced in Northern Europe much farther south than their present location, with the result that the customary warm summers of Europe became unreliable. The last major glacial period, or ice age, ended not too long before the beginning of recorded history, perhaps twelve thousand years ago or a bit more.
During most of human history, changes in the earth's temperature, though they had an effect on the human population, by altering the location and extent of areas that were habitable, did not pose a major threat to humans because there were so few of them on the face of the planet. But in the past century or two, the human population has exploded, with two very important consequences. First, feeding the world's population now requires the industrialization of agriculture. Both the gross output and the year by year reliability of agricultural output is now essential to a population that is primarily urban and completely cut off from arable land or the activity of food production. Second, people have settled along vast stretches of low-lying coastal areas, not only in places like Bangladesh but also in North and South America and Europe. It would take only a relatively minor fluctuation in the earth's average temperature to produce horrendous disruptions both to the food supply and to those coastal settlements. Therefore, it is very much in the interest of the entire world that the temperature of the earth remain quite stable, neither rising nor falling more than a degree or two [which, contrary to one's intuition, is all by itself enough to produce important disruptions.]
Unfortunately, the evidence of the last several billion years makes it clear that the average temperature of the earth does not remain stable over long periods of time. Left to its own devices, the earth grows cooler and warmer all by itself.
So the consensus about the Global Warming controversy, it seems to me, is wrong. The crucial question is not whether carbon emissions are the cause of what appears to be a recent trend of global warming. The only relevant question is whether human activity can, in any way, be a contributing factor in the short-term determination of global temperature. I say "short term," because even if the earth is going to go through another major glaciation some time in the next ten or fifteen thousand years, which is to say a major global cooling, it makes an enormous difference to human beings how the earth's temperature changes in the next several centuries. A two or three century long period of global warming would be perfectly compatible with a thirty thousand year cycle of glaciation. From the perspective of geological time, such a minor variation would be insignificant, even though it might be catastrophic for us and the next fifteen or twenty generations to follow us.
So, it would be very useful to alter the terms of the current debate. Can human activity have a measurable effect on the earth's average temperature, regardless of the underlying causes of long-term temperature cycles? Can we figure out what that effect is? Are there things the world's population can do to tweak the temperature fluctuations so as to dampen potentially catastrophic short-term shifts?
These are the questions we ought to be asking. I am not competent to answer them, though I am impressed by the evidence that the answer to all three of these questions is Yes.