Written by FriendsOfScience.org
The IPCC officially released its Fourth Assessment Report (AR4) in 2007. This document is often regarded as the definitive word on the science behind global warming. However, AR4 gives a distorted, misleading, and often erroneous picture. Examples of these distortions will be listed here each week, with attention focused on the Working Group 1 Report "The Physical Science Basis" (WG1), and in particular its Summary for Policymakers (SPM).
1 August 2008: How the IPCC invented a new calculus. The IPCC authors invented a new way of measuring the slope of a graph, in order to create the false impression that global warming is accelerating.
8 August 2008: The table that didn't add up. The WG1 SPM was approved by the IPCC even though it contained a table with arithmetic errors. The table was quietly corrected with no admission of the error.
15 August 2008: False statement about Antarctic sea ice. The IPCC claims that there is no significant trends in Antarctic sea ice. In fact several papers (ignored by the IPCC) show a significant positive trend.
22 August 2008: Misleading claims about sea level rise. AR4 gives the misleading impression that the rate of sea level rise is increasing, using the trick of switching from one measurement system (tide gauges) to another (satellites).
29 August 2008: Incorrect calculation of an average. An arithmetic error was made in the calculation of an average of a contribution to radiative forcing. Hence four diagrams in AR4 are wrong and misleading.
5 September 2008: False claims about Antarctic ice sheet. The IPCC claims that the Antarctic ice sheet is melting and that this is contributing to sea level rise, but recent research papers show that in fact the ice sheet is thickening.
12 September 2008: Dubious claims about Greenland ice sheet. The IPCC claims that the Greenland ice sheet is melting and causing sea level to rise - ignoring or misrepresenting research that shows the opposite.
19 September 2008: Erroneous claims about snow cover. The IPCC makes the false claim that snow cover is decreasing in both hemispheres.
26 September 2008: Exaggerated claims about water vapour. The IPCC summary claims that water vapour has increased. In fact studies show no significant trend or in some cases a decrease.
3 October 2008: Erroneous claims on increased tropical cyclone activity. The IPCC states that tropical cyclones have increased, but research papers find no evidence of this.
10 October 2008: The IPCC contradicts itself over the medieval warm period. The IPCC's own data shows clear evidence that the medieval warm period was as warm as the late 20th century, but the text states the opposite.
17 October 2008: False statement about paleoclimate studies. The IPCC claims that there is increased confidence in proxy temperature reconstructions, but in fact the opposite is the case.
24 October 2008: Proxies that aren't proxies. The IPCC makes use of 'proxy' data such as tree rings to justify their claim that current temperatures are unusual - but this data doesn't match measured temperature.
31 October 2008: Downplaying the urban heat island effect. The IPCC significantly underestimates the influence of the fact that many temperature measurement sites are located in cities.
7 November 2008: The UN misquotes its own report. A UN press release coinciding with the release of AR4 blatantly misquoted the report, incorrectly claiming that man-made global warming was unequivocal.
14 November 2008: Not the IPCC this week, but a special issue on the latest GISS temperature errors.
21 November 2008: Underestimating past variation in carbon dioxide. The IPCC claims that variation of carbon dioxide levels in the atmosphere was very low, ignoring published research that shows much greater variation.
28 November 2008: Biased reporting of the literature. One of many examples where the IPCC ignores or disparages research that does not support its agenda, in the area of past solar activity.
5 December 2008: Where's the beef? The crucial step of the argument for global warming - how carbon dioxide causes heating - is barely mentioned and the numbers not justified by the IPCC.
12 December 2008: Hypothetical positive feedback. The alarming predictions of the IPCC rely on the assumption of a strong positive feedback, for which there is no evidence.
Acknowledgements: These examples come from many different sources. Many originated from a thread at climate audit, so thanks are due to those who contributed to that - especially Max.