The Errors of Chicken Little Thinking: It Is Highly Unlikely That a Doubling of Human-Caused Greenhouse Gases Will Cause Significant Changes in Global Temperatures
Gray, William M., Forum for Applied Research and Public Policy
By the end of the 21st century the concentration of greenhouse gases from human activity in Earth's atmosphere is expected to double from preindustrial values. Many believe this increase will cause a 2 to 5 degree Celsius (3.6 to 9 degrees Fahrenheit) increase in Earth's temperature. These projections are based largely on government-sponsored U.S. and foreign Global Computer Model simulations.
These computer models use a number of complicated mathematical formulas to simulate the physical processes of the atmosphere and ocean circulation. They forecast future changes in the atmosphere and ocean by simultaneously solving an array of equations that are envisaged to represent the real physical processes of the Earth's climate system. There is some imprecision in the accuracy of these equations with regard to their ability to represent the real atmosphere. Time steps vary from about 15 minutes to an hour or so. They integrate this set of simultaneous equations for hundreds of thousands of time steps into the future. Separate calculations are made, which include and exclude the human-induced greenhouse gas inputs of carbon dioxide and methane. Though these models have become more sophisticated over the past few decades, the methodology appears to be compromised by two basic flaws.
First, the models assume that more rainfall, resulting from the buildup of greenhouse gases, will lead to significant increases in atmospheric water vapor, especially in the upper atmosphere, and in cirrus cloudiness. These increases are presumed to significantly reduce the radiation energy sent back to space. To compensate for this assumed reduction in outgoing radiation to space, the globe must warm so that it can compensate for this reduced energy flux. Energy to space increases with global temperature. Observations and theoretical analysis by myself and others, however, suggest that reductions in outgoing radiation, due to increases in global rainfall, will be very small, and will not cause significant global warming.
A second flaw in the Global Computer Model simulations is their inability to make realistic simulations of ocean circulation processes many decades into the future. Since about 70 percent of the atmosphere is in contact with the ocean surface, ocean circulation patterns are fundamental to climate variability.
The primary greenhouse gas in the atmosphere, by far, is water vapor. It is the influence of the human-caused greenhouse gases, such as carbon dioxide and methane, on water vapor that is most in question. If the addition of human-induced greenhouse gases leads to an enhancement of water vapor's dominant influence (a positive feedback), then humans will, indeed, be responsible for significant warming. But it is more likely that the human-induced gases will act as a modulator (negative feedback) of water vapor's influence. If the human-induced greenhouse gases will act to slightly reduce water vapor's influence as a greenhouse gas, then little global warming will result.
Most researchers agree that the Earth will rid itself of most of the positive energy gains from human-induced greenhouse gas by developing extra surface evaporation and compensating extra global rainfall, which has a cooling effect on the Earth's surface. The key question is how the atmosphere will respond to this expected increase in global evaporation rainfall. Will the expected increase in human-induced greenhouse gases cause a positive, a neutral, or a negative trend in net global outgoing radiation? The Global Computer Models are programmed to give large--and apparently unrealistic--reductions in outgoing radiation to space as global rainfall increases.
As more-realistic computer simulations become available in the future, I believe we will learn that the runaway global warming scenarios predicted by current Global Computer Model technology grossly overestimate the actual threat, and that the small surface warming trends observed in global surface temperature during the last 25 to 100 years, which have been so highly touted in the press, are primarily of natural origin and not due to human influences. …