As physicist Richard Muller calls it in his article in Technology Review. It turns out that the famous "hockey stick" graph which purports to show that the last 100 years were the warmest years in the last 1000 years is a result of a bad statistical analysis. The United Nations' Intergovernmental Panel on Climate Change relied heavily on the "hockey stick" as evidence for its conclusion that man-made global warming is a growing and serious problem.
Earlier this year, I spoke with Ross McKitrick, one of the researchers who questioned the "hockey stick." McKitrick was surprised (dismayed?) about how much resistance his analysis was getting from the "scientific community." McKitrick also told me that climatologist Michael Mann, the creator of the "hockey stick," started pulling his data from his website when he found out that McKitrick and McIntyre were re-analyzing it. So much for scientific reproducibility and openness.
The fact that the "hockey stick" is hooey doesn't mean that there is no man-made global warming, but it may well mean that natural variations in global climate are much greater than the perturbations caused by human activities. As many scientific papers often conclude: Further research is needed.