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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 11, NUMBER 8, AUGUST 1998

NEWS...
Feature of the Month: Satellite Temperatures

Item #d98aug31

A firestorm of debate was ignited several months ago when a manuscript submitted for publication in Nature was leaked to the press. The article challenged some of the atmospheric temperatures reported by satellites. It stated that the values published, which indicated that the portions of the atmosphere observed were exhibiting a cooling trend rather than the warming trend ascribed by surface measurements, were too low. It charged that the orbital decay of the satellites was not being taken into account in the processing of the satellite data. As a result, the proper distances were not being used when the satellite data were converted into atmospheric temperatures. The manuscript went on to say that, when the repositioning of the satellites was taken into account, the calculations showed an increase between 1979 and 1995 in the atmospheric temperatures measured by the satellites, not a decrease.

These satellite measurements have long been used by some to question the existence of global warming. Among other arguments, they have pointed out that the surface-derived temperature record is imperfect in that (1) the instruments used vary from location to location and from time to time and (2) the locations at which measurements are taken are unevenly distributed around the globe (largely clustered on landmasses, in developed countries, and at airports) and are occasionally moved. Satellites can have the ability to take measurements more or less uniformly around the globe, and those measurements can be readily integrated. For these reasons, the scientific community has placed great confidence in satellite remote-sensing values for decades.

The refereed article was published in Nature in August (see Wentz and Schabel article in Prof. Pubs./Of General Interest in this issue). In the intervening months, many recalculations of the satellite data have been carried out and reported informally [“New Evidence for Global Warming,” Bette Hileman, C&E News 76 (33), 7-8 (Aug. 17, 1998); “Satellites Misread Global Temperatures,” R. Monastersky, Science News 154, 100 (Aug. 15, 1998); “Falling Satellites, Rising Temperatures?” D. J. Gaffen, Nature 394, 615-616 (Aug. 13, 1998); “A Heated Controversy,” The Economist (15 August 1998)].

All of those recalculations reflect warmer temperatures than were originally reported. Some still show a decrease in average atmospheric temperature, albeit a smaller decrease than before. None of new values agree with the temperature increases measured at the surface, but they should not because different entities are being measured.

A formal publication of the recalculated values derived by the person who developed the method for measuring temperatures with microwave sounding units is in preparation.