Why I am Skeptical of Claims About “Global Warming”


Robert Sheaffer – April, 2008


Let me begin by acknowledging that I am not a climate scientist. However, I have been an active skeptic, a defender of the scientific method, and a student of the history of science for many years. One hears a great deal today, mostly from partisan political sources, about a supposed “scientific consensus” on severe anthropogenic (human-caused) global warming (AGW). But when a prominent theory is opposed by scientists of the caliber of Richard Lindzen of MIT, Reid Bryson of the University of Wisconsin, Freeman Dyson of the Institute for Advanced Study, and many others, it is disingenuous to speak of a “consensus.” Indeed, there is reason to believe that the so-called “consensus” is largely illusory, although there are no doubt many qualified climate scientists who fully accept AGW. One should also be aware of the social, political, and financial pressures placed upon scientists to conform to this (mostly) political and (partly) scientific orthodoxy. One should recall the words of Freeman Dyson, writing in the 1980s about “Nuclear Winter,” another wobbly scientific hypothesis that was being hyped by the Academic Left to try to prevent Reagan’s military build-up to counter that of the Soviets: “As a scientist, I judge the nuclear winter theory to be a sloppy piece of work, full of gaps and unjustified assumptions. As a human being, I hope fervently that it is right… I do not blame those who have muffled their criticisms. Nobody wants to be put publicly in the position of saying that, after all, nuclear war may not be so bad. It is difficult to criticize nuclear winter publicly without giving an appearance of moral insensitivity. The majority of scientists who have doubts about nuclear winter keep their doubts private.” (Infinite in All Directions, Chapter 15). No doubt the very same pressures are being felt today over “Global Warming”, whose political use looks suspiciously like Nuclear Winter Redux.


Is the earth getting warmer? It appears to be warmer now than it was in the 1960s and 70s, although the exact degree of warming is in question. It is also not certain whether the warming trend is continuing, or is stopping and possibly reversing; there is considerable evidence to suggest the latter. The 1920s and 30s were at least as warm as the present time. An article in the Washington Post dated Nov. 2, 1922, states “Arctic Ocean getting warm; seals vanish and icebergs melt.” NASA now acknowledges, after correcting previous errors, that the warmest year on record was 1934 (the time of the “dust bowl”).  Do not forget that during the 1970s there were scientists warning of “Global Cooling” and a possible new ice age. ( Time, June 24, 1974;  Newsweek, April 28, 1975. )  These changes in the earth’s temperatures do not correspond to changes in the level of CO2. The causes of this and other observed climate variations are unknown.


Even larger variations in climate have occurred during historic times. It is now well-known that there was what is called the “Medieval warm period” in climate from approximately 800-1300. At this time, Greenland was inhabitable and was settled by Vikings. As the climate cooled after 1300, these settlements died out. Next came the “Little Ice Age” from about 1300 to 1900. There appear to have been three temperature minima, occurring around 1650, 1770, and 1850, each separated by slightly warmer temperatures in between. The cause of these major climate variations is unknown, although changes in solar activity are one plausible proposed explanation. The period of unusually low solar activity known as the Maunder Minimum corresponds to the lowest temperatures of the Little Ice Age, and the Spörer Minimum was also a period of significant cooling at the beginning of the Little Ice Age. These very significant changes in the earth’s temperatures do not correspond to changes in the level of CO2.


The earth has experienced at least four separate periods known as “Ice Ages”, when glaciers the size of continents advanced, then retreated. Each one had its own periods of warming and cooling within the glacial periods. While theories abound, the cause of the Ice Ages is unknown. The earth is presently in the process of warming up following the end of the most recent Ice Age approximately 10,000 years ago, so it is not surprising to see temperatures gradually increasing. It is not known whether, or when, another ice age may occur. It is reasonable to presume that we are presently in a warm interglacial period, and that a future Ice Age will probably recur, although not anytime soon. Before the most recent series of Ice Ages began, approximately 40 million years ago, the earth’s climate was much warmer than it is today. The cause of this is unknown.


In summary, the earth’s climate has undergone extremely significant changes in its observed history, and the causes of these changes are largely unknown. This brings up an obvious question that nobody seems willing to ask: given that unknown factors have caused previous climate changes, how can we be certain that these same unknown factors are not active today? Whatever factors are causing present-day warming might well be the same ones that caused any of these earlier warming periods. They cannot be ruled out, because we don’t even know what they were.  Nobody understands the causes of historical climate changes, yet the warmists claim to understand Earth’s future climate perfectly.


Data is Unreliable. Just recently, a private survey of stations of the U.S. Historical Climate Record has turned up results that can only be called astonishing. A very significant number of these stations are set up in flagrant violation of NOAA’s weather station siting guidelines. Temperature measurements are being made on or near asphalt, air conditioner exhaust ducts, and in many other unsuitable places. These invalid measurements constitute a significant portion of the data used to support “global warming.” Currently the private survey is only approximately 1/3 completed. Once each station has been surveyed, and the invalid ones identified, all of the data from invalid stations needs to be removed from the database, and new temperature calculations based solely on the valid stations.


Environmentalism - Crying Wolf for 40 years.




1967: Famine 1975! by William and Paul Paddock. It proclaimed the inevitability of massive famines by 1975, and recommended cutting off all aid to countries deemed “hopeless.” A review in Science magazine proclaimed, “all responsible investigators agree that the tragedy will occur" (i.e., a scientific consensus).




1972: Limits to Growth by the Club of Rome.


1980: The Carter administration published in 1980 its multiagency assessment of the earth’s future, titled Global 2000. Its famous doom-and-gloom forecast that "the world in 2000 will be more crowded, more polluted, less stable ecologically. . . . and the world’s people will be poorer in many ways than they are today" received headlines across the nation. Malthusianism was now the official position of the U.S. government.