To great fanfare, on January 20 the United Nations’ Intergovernmental Panel on Climate Change (IPCC) approved and released the “Summary for Policymakers” of its Third Assessment Report.  The summary was widely reported in the media around the world as further proof of the dangers of global warming. The problem, however, is that (as with the Second Assessment Report in 1995) the summary bears little resemblance to the actual report, which has not yet been approved for final release. The report itself is replete with caveats that give little support for the catastrophic global-warming scenario touted by anti-energy activists (commonly known as environmentalists).
Political document. The summary, on the other hand, is a political document that exists primarily to bolster the claims of the anti-energy zealots. As Robert Watson, chairman of the IPCC, said in a press conference releasing the summary, “This adds impetus for governments of the world to find ways to live up to their commitments…to reduce emissions of greenhouse gases.” 
This “impetus” comes from the summary’s claims that the earth’s temperature could rise much faster than previously thought, and that the last century was the warmest in the past 1000 years. The Second Assessment Report, which was released in 1995, predicted that the earth could warm by 1 to 3.5 degrees centigrade by the year 2100. The “best estimate” was a 2-degree-centigrade warming by 2100. The new report has dramatically increased that estimate to 1.4 to 5.8 degrees centigrade, even though no new evidence has come to light to warrant such a dramatic change.
Unlikely scenario. The new prediction is based on a change in assumptions about such things as population growth, economic growth, and fossil fuel use. The extreme-case scenario of a 5.8-degree warming, for instance, is based on an assumption that the whole world will raise its level of economic activity and per capita energy use to that of the United States, and that energy use will be carbon intensive. This scenario is extremely unlikely, yet it has featured prominently in news stories around the world because it results in the biggest fear effect.
The summary also claims that the 20th century has been the warmest in the last 1000 years. This conclusion is based on a suspect set of data derived from tree rings, which purports to show a stable climate from the years 1000 to 1900. It then crudely attaches the 20th century surface-based thermometer data to produce a dramatic warming thereafter. When these two different (and incompatible) data sets are combined, the resulting graph resembles a hockey stick lying on its back, blade up.
It is very difficult to extract any information about past temperature variations using tree-ring data. What it does tell us is whether the “combined micro-environmental conditions during the growing season [of a particular year] were favorable to [tree] growth or not.”  These conditions include rainfall, temperature, atmospheric carbon dioxide concentrations, and so on. Singling out the temperature effect is a highly speculative business. Moreover, the samples used in the tree-ring data were limited to the Northern Hemisphere, leaving much of the planet unsampled. The IPCC report, nonetheless, presents the hockey-stick graph as representing a global temperature trend.
Radical hockey stick. The hockey stick represents a radical departure from the well-established historical temperature record, which has been derived from several proxies, including the written historical record, ice core samples, and tree-ring data, among others. Those records show that the earth was much warmer during the Medieval Warm Period, from around 1000 to 1300. The 20th century was cooler than the Medieval Warm Period, and the warming that has occurred could easily be explained by a natural emergence from the Little Ice Age (1300-1850), an episode that also mysteriously disappears in the IPCC’s new tree-ring data.  Indeed, the amount of warming claimed for the 20th century is smaller than the margin of error in the IPCC’s temperature data. 
The summary states, “There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.”  It turns out, however, that the evidence comes from computer-generated climate models, which, of course, isn’t evidence at all.
“There is a longer and more closely scrutinized temperature record and new model estimates of variability,” says the summary. “The warming over the past 100 years is very unlikely to be due to internal variability alone, as estimated by current models.”  Why the internal variability estimated by computers is valid is not explained. A look at real climate variability over the long term clearly shows that the current warming is well within natural variability.
Finally, computer models are still incapable of replicating the present climate using known climate conditions. Moreover, the several models in existence give such widely divergent predictions it is difficult to know what to make of them. A model that cannot predict the present certainly shouldn’t be used to predict 100 years into the future. Nor should it serve as a basis for energy-deprivation policies.
  The “Summary for Policymakers” can be found at www.ipcc.ch . The IPCC is a UN agency charged with providing an overview of climate science. Its assessment reports, which are released every five years, claim to represent the scientific community’s consensus on global warming. But as noted by Dr. Richard S. Lindzen, the Alfred P. Sloan Professor of Meteorology at the Massachusetts Institute of Technology, and a lead author of the IPCC report, “The public is led to think that hundreds, even thousands, of scientists formed a consensus about this report. The truth is that we’re not even asked.” Peter Calamai, “Top Scientists Call U.N. Report on Climate Change Misleading,” Toronto Star, January 23, 2001.
  Philip P. Pan, “Scientists Issue Dire Warning on Warming; Faster Climate Shift Portends Global Calamity this Century,” Washington Post, January 23, 2001.
  H.H. Lamb, Climate, History and the Modern World (New York: Routledge, 1985).
  “Summary for Policymakers,” Figure 1(b).
  Ibid., p. 6.
  Ibid.