My friend Matt Ridley gave the Angus Millar Lecture of the Royal Society of the Arts Edinburgh on Halloween. His title was "Scientific Heresy." Ridley cogently explains why he thinks that massive confirmation bias is behind the claims that man-made global warming is potentially catastrophic. Here's the heart of his talk:

I was not always such a 'lukewarmer'. In the mid 2000s one image in particular played a big role in making me abandon my doubts about dangerous man-made climate change: the hockey stick. It clearly showed that something unprecedented was happening. I can remember where I first saw it at a con- ference and how I thought: aha, now there at last is some really clear data showing that today's temperatures are unprecedented in both magnitude and rate of change – and it has been published in Nature magazine.

Yet it has been utterly debunked by the work of Steve McIntyre and Ross McKitrick. I urge you to read Andrew Montford's careful and highly readable book The Hockey Stick Illusion. Here is not the place to go into detail, but briefly the problem is both mathematical and empirical. The graph relies heav- ily on some flawed data – strip-bark tree rings from bristlecone pines – and on a particular method of principal component analysis, called short centering, that heavily weights any hockey-stick shaped sample at the expense of any other sample. When I say heavily – I mean 390 times.

This had a big impact on me. This was the moment somebody told me they had made the crop circle the night before. For, apart from the hockey stick, there is no evidence that climate is changing dangerously or faster than in the past, when it changed naturally. It was warmer in the Middle Ages and medieval climate change in Greenland was much faster.

Stalagmites, tree lines and ice cores all confirm that it was significantly warmer 7000 years ago. Evidence from Greenland suggests that the Arctic ocean was probably ice free for part of the late summer at that time. Sea level is rising at the unthreatening rate about a foot per century and decelerating. Greenland is losing ice at the rate of about 150 gigatonnes a year, which is 0.6% per century. There has been no significant warming in Antarctica, with the exception of the peninsula. Methane has largely stopped increasing. Tropical storm intensity and frequency have gone down, not up, in the last 20 years. Your probability of dying as a result of a drought, a flood or a storm is 98% lower globally than it was in the 1920s. Malaria has retreated not expanded as the world has warmed.

And so on. I've looked and looked but I cannot find one piece of data – as opposed to a model – that shows either unprecedented change or change is that is anywhere close to causing real harm….

Meanwhile, I see confirmation bias everywhere in the climate debate. Hur- ricane Katrina, Mount Kilimanjaro, the extinction of golden toads – all cited wrongly as evidence of climate change. A snowy December, the BBC lectures us, is 'just weather'; a flood in Pakistan or a drought in Texas is 'the sort of weather we can expect more of'. A theory so flexible it can rationalize any outcome is a pseudoscientific theory.