Steve McIntyre of Climate Audit caught Professor Michael Mann of hockey stick fame misleading people about the quality of global climate models at the December 2012 American Geophysical Union meeting.
A problem for those who are convinced that mankind’s activities are influencing global temperature is that, as the top chart from the IPCC shows, recent observations of land-and-ocean temperature (red line) are considerably lower than midrange temperature model predictions (blue line). [The red and blue lines were added by McIntyre to aid in discussing the chart.] In fact, as previously reported at this blog, there has been no warming for the past 15 years.
The second chart is a bad photo of one that Mann used in his talk with, once again, the red and blue lines added by McIntyre for emphasis. Two tricks minimize the difference between observation and predicted temperatures. First, this graph plots land temperatures (red line) which are always warmer than land-and-ocean temperatures. The Climate Audit site has an animated graphic showing just how much they differ. It also offers additional photos, and a clearer chart showing that similar data manipulation was used at an earlier talk at Rugters.
Second, the graph only provides temperature data to 2005 even though the talk occurred in 2012.
The result is a slide that made it look like observed temperatures agree with the models that forecast global warming, a result not supported by the IPCC graph.