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The Prosecutor’s Fallacy and the IPCC Report

New paper reveals classic logical fallacy in IPCC report

A new paper from the Global Warming Policy Foundation reveals that the IPCC’s 2013 report contained a remarkable logical fallacy. The author, Professor Norman Fenton, shows that the authors of the Summary for Policymakers claimed, with 95% certainty, that more than half of the warming observed since 1950 had been caused by man. But as Professor Fenton explains, their logic in reaching this conclusion was fatally flawed.

Given the observed temperature increase, and the output from their computer simulations of the climate system, the IPCC rejected the idea that less than half the warming was manmade. They said there was less than a 5% chance that this was true.

But they then turned this around and concluded that there was a 95% chance that more than half of observed warming was manmade.”

This is an example of what is known as the Prosecutor’s Fallacy, in which the probability of a hypothesis given certain evidence, is mistakenly taken to be the same as the probability of the evidence given the hypothesis.

As Professor Fenton explains 

“If an animal is a cat, there is a very high probability that it has four legs. However, if an animal has four legs, we cannot conclude that it is a cat. It’s a classic error, and is precisely what the IPCC has done.”

Professor Fenton’s paper is entitled The Prosecutor’s Fallacy and the IPCC Report. Click image to download.

The Prosecutor's Fallacy and the IPCC Report - cover
Click to download