Measuring the Temperature of Earth From Space

Even with Needed Corrections, Data Still Don't Show the Expected Signature of Global Warming

Scientist's Notebook

By  Dr. Roy Spencer  Senior Scientist for Climate Studies  NASA/Marshall Space Flight Center

14 August 1998 

The paper published by Wentz and Schabel in Nature this week (August 14, 1998) is bound to generate controversy about the satellite measurements of global tropospheric temperatures. These measurements, for the period since 1979, have been made with the TIROS-N satellite Microwave Sounding Units (MSUs) by myself and Dr. John Christy (The University of Alabama in Huntsville). We are grateful to Wentz and Schabel for discovering the first convincing evidence for needed corrections to our satellite-based global temperatures. 

However, we believe that there are a few important points that should be considered when reporting on this paper. 

1) The spurious cooling in the satellite record due to the orbital decay ("downward drift") effect was only estimated by Wentz and Schabel as an average adjustment to our processed satellite data.  The effect, which will have different values for the eight different satellites in the record, should instead be removed one satellite at a time before the satellites in the record are intercalibrated.  We (John Christy and Roy Spencer) have performed this adjustment, with the results given below.

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2) The effect reported by Mr. Wentz had been partly offset by an east-west drift in the satellites' orbits. The valuable discovery of the downward drift effect by Wentz and Schabel allowed us to separately quantify two consequences of the east-west drift (MSU instrument temperature change, and observation time-of-day change). We have now performed these adjustments as well (below). 

3) The global decadal temperature trends, for the period 1979-1997, from the various satellite, weather balloon, and surface temperature measurements are as follows, in order of increasing temperature trend: 
 

 
It can be seen that the adjustment by Wentz and Schabel does not agree with our (more complete) adjustments, or to the weather balloon data. Instead, their adjustment comes closer to the surface thermometer measurements, and herein lies a temptation to jump to conclusions. 

4) The adjusted satellite trends are still not near the expected value of global warming predicted by computer climate models. The Intergovernmental Panel on Climate Change's (IPCC) 1995 estimate of average global warming at the surface until the year 2100 is +0.18 deg. C/decade. Climate models suggest that the deep layer measured by the satellite and weather balloons should be warming about 30% faster than the surface (+0.23 deg. C/decade). None of the satellite or weather balloon estimates are near this value. 

5) 1998 UPDATE: The last six months of our adjusted satellite record (February through July 1998) were the warmest in the 20 year record. The updated trend is now +0.04 deg. C/decade (which is still only 1/6th of the IPCC-expected warming rate). The current demise of El Nino, and the possibility of a La Nina forming, will likely cause significant cooling in the coming months. 
 
 

Related links

Global Hydrology and Climate Center in Huntsville, Alabama  December 1997 is Coldest Month on Record in the Stratosphere - Space-based measurements of the  temperature of the Earth's lower stratosphere indicate that December 1997 was the coldest month on record since measurements of this type were begun in 1979.  Accurate "Thermometers" in Space  NASA/Marshall Science Headlines  How dry is the tropical free troposphere? NASA/Marshall Science Headlines  Global Climate Modeling: The Accuracy of Satellite Data  NASA/Marshall Science Headlines  See the Data for Yourself: Updated Stratospheric and Tropospheric Temperature Data from Space

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Author: Dr. Roy Spencer 
Curator: Linda Porter  
NASA Official: Gregory S. Wilson