At the highest level, these are the conclusions of Climate Change Reconsidered:
* The IPCC claims to find evidence in temperature records that the warming of the twentieth century was "unprecedented" and more rapid than during any previous period in the past 1,300 years. But the evidence it cites, including the "hockey-stick" representation of earth's temperature record by Mann et al., has been discredited and contradicted by many independent scholars.
* A corrected temperature record shows temperatures around the world were warmer during the Medieval Warm Period of approximately 1,000 years ago than they are today, and have averaged 2-3ºF warmer than today's temperatures over the past 10,000 years.
If you want to inform yourself about the global warming debate, there is no better place to begin.
* Evidence of a global Medieval Warm Period is extensive and irrefutable. Scientists working with a variety of independent methodologies have found it in proxy records from Africa, Antarctica, the Arctic, Asia, Europe, North America, and South America.
* The IPCC cites as evidence of modern global warming data from surface-based recording stations yielding a 1905-2005 temperature increase of 0.74ºC +/- 0.18ºC. But this temperature record is known to be positively biased by insufficient corrections for the non-greenhouse-gas-induced urban heat island (UHI) effect. It may be impossible to make proper corrections for this deficiency, as the UHI of even small towns dwarfs any concomitant augmented greenhouse effect that may be present.
* Highly accurate satellite data, adjusted for orbit drift and other factors, show a much more modest warming trend in the last two decades of the twentieth century and a dramatic decline in the warming trend in the first decade of the twenty-first century.
* The "fingerprint" or pattern of warming observed in the twentieth century differs from the pattern predicted by global climate models designed to simulate CO2-induced global warming. Evidence reported by the U.S. Climate Change Science Program (CCSP) is unequivocal: All greenhouse models show an increasing warming trend with altitude in the tropics, peaking around 10 km at roughly twice the surface value. However, the temperature data from balloons give the opposite result: no increasing warming, but rather a slight cooling with altitude.
* Temperature records in Greenland and other Arctic areas reveal that temperatures reached a maximum around 1930 and have decreased in recent decades. Longer-term studies depict oscillatory cooling since the Climatic Optimum of the mid-Holocene (~9000-5000 years BP), when it was perhaps 2.5º C warmer than it is now.
* The average temperature history of Antarctica provides no evidence of twentieth century warming. While the Antarctic peninsula shows recent warming, several research teams
have documented a cooling trend for the interior of the continent since the 1970s.