Here’s an IPCC error we don’t hear reported too often. This picture from the 2009 Copenhagen Diagnosis illustrates how far out the IPCC’s 2007 Fourth Assessment Report was in predicting reduction in Arctic sea ice extent. The black line is a combined (ensemble) figure of a range of simulations, and the dashed lines represent the highest and lowest values of the simulations. The red line is the measured sea ice extent.
Since 2007, when sea ice extent reached an all-time minimum (in recorded history), many climate deniers have made a big thing of how sea ice extent has “recovered”. Since this graph was made, sea ice extent has fluctuated a bit, without hitting the 2007 low again, but still well below simulations reported by the IPCC.
The other thing climate deniers have done is attack the IPCC wildly whenever a trivial error has been spotted. Guys, this is a big one. I’m waiting for you all to get excited.