Managing Editor’s note: The following letter to the editor, reprinted here with permission, was submitted to the IEEE Spectrum (Forum) in response to “Capturing Climate Change,” a review paper on global warming written by Tekla S. Perry and published in the January 2002. IEEE is the Institute of Electrical and Electronics Engineers, Inc. Giger is an IEEE fellow.
I was disappointed that the review paper on global warming did not mention the most important experimental data related to global warming, namely the temperature measurements of the lower troposphere that have been made by Tiros-N satellites over the past 23 years.
These are the only precision measurements of global temperature available for direct comparison with temperature predictions from computer climate models, the so-called General Circulation Models (GCM).
Twice a day the 53.74 GHz microwave radiometers in the Tiros satellites, working at the lower end of the 60 GHz oxygen absorption line, cover the whole Earth, measuring and averaging the temperature of all the oxygen molecules in the lower troposphere from the surface up to about 8 km with maximum weighting at 5 km. This is the same region modeled by the GCMs. The accuracy of the radiometer measurements is 0.01° C, which is considerably better than the accuracy of thermometer measurements made on the surface of the Earth.
The monthly lower tropospheric temperature averages are available from the NASA Web site, http://science.nasa.gov/newhome/essd/essd_strat_temp.htm, beginning with January 1979. The monthly averages may fluctuate by as much as ± 0.5° C, but linear regression gives a temperature increase of only 0.08° C over the 23-year measuring period. The proponents of global warming attribute this to the increase in the manmade greenhouse gas carbon dioxide .
The greenhouse effect is the phenomenon where infrared radiation (heat) emanating from the Earth’s surface is absorbed by greenhouse gases, mainly water vapor and carbon dioxide, which make up less than 1 percent of all atmospheric gases. This effect makes our planet inhabitable by warming the Earth’s surface about 33° C , of which 32° is due to water vapor and 1° C due to carbon dioxide.
The satellite measurements indicate that this temperature has increased by 0.08° C over the past 23 years. We also know that the carbon dioxide content in the atmosphere has gone up by 9 percent over the same period of time, which would explain a temperature increase of 0.09° C (9 percent of 1° C), very close to the measured value of 0.08° C.
Also, according to the climate models, the temperature increase at the surface of the Earth should be about 23 percent less, or 0.06° C. If we use linear extrapolation, the temperature increase over the next 100 years will be 0.26° C, which would be a minuscule amount of global warming.
The latest results from computer models, contained in the 2001 report of the International Panel on Climate Change (IPCC), are in conflict with the above results since they give a surface increase of 0.5° C over the 1979 to 2001 period, and an estimated increase of 1.4° to 5.8° C by the end of the century. This huge discrepancy may be due to the GCMs not including or accurately describing all the underlying physical phenomena, and/or by uncertainties in the physical input variables.
If these GCMs are used to attack the even more difficult problem of local, regional, or temporal temperature behavior, their results have to be judged again by how well they duplicate the precision measurements made by the Tiros satellites.
Finally, temperature measurements using thermometers on the surface of the Earth indicate an increase of 0.5° C over the recent 23-year period, compared to the 0.06° C obtained from satellite measurements. It is possible that the surface thermometer measurements are real, thus indicating a possibility for global warming, but the true causes are not known and cannot be due to carbon dioxide. It may also be the case that the thermometer data are inaccurate due to non-uniform global data gathering, urban heat-island effects, differences in calibration, and general reliability problems.