August 12, 1998

NASA Science News: A new global warming controversy?

NASA scientist Dr. Roy Spencer has responded (link below) to the research paper, published in the August 14 issue of Nature, attacking the satellite data. It should be noted that the paper's main author, Mr. Frank Wentz, who holds a master's degree in physics, is an expert solely on the technical aspects of remote sensing systems. He does not have the expertise to evaluate climate change. Moreover, even with the recommended corrections to the data applied correctly, the adjusted satellite trends are still not near the expected value of global warming predicted by computer climate models.

Comments by S. Fred Singer

Satellite Data

Weather satellites are the only available means for obtaining truly global data.  The use of a single instrument on the satellite also avoids the problem of intercalibration, which is common to both surface thermometers and to radiosondes carried in balloons.  The microwave sounding unit (MSU) carried by the satellite records the integrated emission into space from the well-mixed atmospheric molecular oxygen.  Channel 2 of the MSU covers a broad region of the troposphere and some of the lower stratosphere.  In order to concentrate the altitude range to the lower tropopause, the principal investigators, John Christy and Roy Spencer, have constructed a synthetic channel, 2R, obtained by combining the radiation from different view angles.  For this reason, Channel 2R is somewhat noisier than Channel 2 and also sensitive to satellite altitude.

Because of the importance and uniqueness of the satellite data, they have been subject to intense scrutiny, which has lead to lively discussion in the scientific literature.  Most recently, Wentz and Schabel [1998] pointed to the fact that the orbital decay of the satellites (due to air resistance) introduces a bias in the analysis of Channel 2R, leading to an artificial cooling trend.  While this critique seems to be correct and is accepted by Christy and Spencer, they identify the drift of the satellite orbit plane with respect to the Sun-Earth line and a slight change in the calibration of the instrument as offsetting factors that produce an artificial warming trend. 

According to the principal investigators, the fully corrected satellite data still show a slight cooling trend between 1979 and 1997.  (The El Nino of 1998 produced an unusually strong warming in the tropical regions, sufficient to turn the trend into a slight warming; it is expected that the La Nina in the last part of 1998 may restore the cooling trend.)  The same trends are also observed in the balloon data covering the same period as the satellites; this is a strong argument in favor of the basic correctness of the satellite data.

Go to Dr. Spencer's response.