Chapter 1 describes the limitations of the IPCC’s attempt to forecast future climate conditions by using computer climate models. The IPCC violates many of the rules and procedures required for scientific forecasting, making its “projections” of little use to policymakers. As sophisticated as today’s state-of-the-art models are, they suffer deficiencies and shortcomings that could alter even the very sign (plus or minus, warming or cooling) of earth’s projected temperature response to rising atmospheric CO2 concentrations. If the global climate models on which the IPCC relies are not validated or reliable, most of the rest of the AR4, while it makes for fascinating reading, is irrelevant to the public policy debate over what should be done to stop or slow the arrival of global warming.

Chapter 1 Key Findings

• The IPCC places great confidence in the ability of general circulation models (GCMs) to simulate future climate and attribute observed climate change to anthropogenic emissions of greenhouse gases.

• The forecasts in the Fourth Assessment Report were not the outcome of validated scientific procedures. In effect, they are the opinions of scientists transformed by mathematics and obscured by complex writing. The IPCC’s claim that it is making “projections” rather than “forecasts” is not a plausible defense.

• Today’s state-of-the-art climate models fail to accurately simulate the physics of earth’s radiative energy balance, resulting in uncertainties “as large as, or larger than, the doubled CO2 forcing.”

• A long list of major model imperfections prevents models from properly modeling cloud formation and cloud-radiation interactions, resulting in large differences between model predictions and observations.

• Computer models have failed to simulate even the correct sign of observed precipitation anomalies, such as the summer monsoon rainfall over the Indian region. Yet it is understood that precipitation plays a major role in climate change.

Chapter 1. Global Climate Models and Their Limitations (PDF, 143 kb)

     1.1. Models and Forecasts (PDF, 58 kb)

     1.2. Radiation (PDF, 63 kb)

     1.3. Clouds (PDF, 73 kb)

     1.4. Precipitation (PDF, 60 kb)