Recently, James Hansen wrote about computer climate models having major shortcomings. This is not a surprise to the well informed on climate issues, since it has become very obvious that climate models have wildly overestimated global warming over the last 15 years. There is no argument about this...global warming over the last 15 years has literally disappeared.
(chart updated with April 2011 temperature data; click on the chart to enlarge)
This chart helps one to visually understand the significant and robust failure of climate models. The green curve represents NASA/Hansen climate model predictions of global temperatures if the world did not attempt to control human CO2 emissions and just let CO2 emissions grow. In fact, the world has not controlled CO2 emissions, and the CO2 emissions continue to grow, but the actual global temperatures (black and red curves) are well below that predicted green curve temperature outcome.
To add to the IPCC/NASA climate modeler's misery, current global temperatures are even below the predicted temperature outcome (light blue - cyan curve) if the world had been able to stop CO2 emissions growth.
One can safely surmise, from the above, that all the empirical evidence points to climate models being programmed to be way too sensitive to atmospheric CO2 levels.
Again, we will state the obvious: climate models are absolutely worthless as prediction tools, including predicting global temperature averages.
Additional climate-model postings. Additional modern temperature charts.