A Paucity of Evidence, pt. 3 - As mentioned previously, divergences between predictive models of global warming and observed temperatures have been noted both in scholarly reports and in presentations to congressional subcommittees. In written testimony given on July 20, 2006 to the House Committee on Government Reform, Dr. John Christy, Ph.D. described the results of a paper that he coauthored with three other investigators regarding temperature trends in California since 1910.

Dr. Christie, a Professor of Atmospheric Science at the University of Alabama in Huntsville, described how he and his colleagues collected available surface temperature data from California’s San Joaquin Valley and the nearby Sierra Nevada mountains in order to determine temperature trends. Dr. Christie discovered that nighttime temperatures in the Valley were indeed warming by approximately 6° F, while daytime temperatures fell by about 3° F, and concluded that these temperature changes were consistent with urbanization and irrigation patterns in the area.

But what most intrigued Dr. Christy’s group was the fact that there was no change in recorded temperatures for the Sierra foothills and mountains, which would not have been affected by urbanization or irrigation. Dr. Christy noted that these observed results did not correlate with the results predicted by downscaled models for California.

Models suggest that the Sierra’s are the places where clear impacts of greenhouse warming should be found, but the records we produced did not agree with that hypothesis. The bottom line here is that models can have serious shortcomings when reproducing the type of regional changes that have apparently occurred. This also implies that they would be ineffective at projecting future changes with confidence, especially as a test of the effectiveness for specific policies. In other words it will be almost impossible to say that a specific policy will have a predictable or measurable impact on climate.

Adding to the confusion is that while the U.N.'s Intergovernmental Panel on Climate Change (IPCC) claims to have a fair level of understanding of the effects of greenhouse gases on the warming of the lower atmosphere, they seem to have minimal understanding of other heating factors such as heat produced through biothermal or geothermal processes or waste heat produced by human activities besides the burning of fossil fuels.

The IPCC also admits to having little or no understanding of the cooling effects of such things as stratospheric ozone, airborne sulphates (so-called “white” aerosols that reflect solar radiation), organic carbons generated by the burning of fossil fuels, the indirect effects of volcanic aerosols (such as those emitted in the 1991 eruption of Mount Pinatubo in the Philippines) or the impact of the earth itself on concentrations of greenhouse gases (i.e.: the absorption or release of CO2 by soil and oceans.) Even the conversion of “green spaces” from forests to cropland has been shown to have a cooling effect on the climate. As far back as 1995, the IPCC acknowledged it's lack of certainty.

Our ability to quantify the human influence on global climate is currently limited because the expected signal is still emerging from the noise of natural variability, and because there are uncertainties in key factors. These include the magnitude and patterns of long-term natural variability and the time-evolving pattern of forcing by, and response to, changes in concentrations of greenhouse and aerosols, and land-surface changes.

The potential cumulative impact of all of these influences may either potentiate or overcome any warming caused by greenhouse gases. But given that the IPCC’s understanding of cooling factors is limited at best, it is unlikely that they have been completely factored into the models used to describe future global warming.