Roy Spencer, John Christy, and William Braswell of the University of Alabama in Huntsville (UAH) Earth System Science Center recently released Version 6 (V.6) of their global satellite temperature dataset. The scientists describe the upgrade, which took three years to complete, as “by far the most extensive revision of the procedures and computer code we have ever produced in over 25 years of global temperature monitoring.”
Compared to the previous UAH dataset (V5.6), the most important change is a reduction in the global average lower-troposphere temperature trend from +0.140°C/decade to +0.114°C/decade over the past 36 years (Dec. ’78 through Mar. ’15).
Figure explanation: Monthly global-average temperature anomalies for the lower troposphere from Jan. 1979 through March, 2015 for both the old and new versions of LT (top), and their difference (bottom).
The revision is noteworthy in several respects. First, as the scientists point out, the UAH dataset more closely matches the Remote Sensing Systems (RSS) dataset, a separate satellite monitoring program, which shows no net warming since Dec. 1996. In the RSS record, the length of the warming pause is now 18 years five months.
Second, a warming trend of +0.114°C/decade is roughly what scientists would expect in a low-sensitivity climate where feedbacks do not strongly amplify the direct warming effect of rising carbon dioxide (CO2) concentrations. For perspective, in a hypothetical zero feedback climate, a doubling of atmospheric CO2 concentration would increase the temperature of the surface-troposphere system by 1.2°C, according to the IPCC.
Third, the UAH V.6 record would appear to cast doubt on the IPCC’s claim of greater than 95% certainty that more than half of all warming since 1951 is due to anthropogenic greenhouse gas emissions.
One of the IPCC’s main lines of evidence for anthropogenic climate change is a warming of the troposphere (lowest region of the atmosphere) combined with a cooling of the stratosphere (the layer above the troposphere). As explained by Dr. Ben Santer of the Lawrence Livermore National Laboratory, if the Sun were responsible for global warming, then the stratosphere should also get warmer. Instead, the stratosphere has cooled since 1979, which is consistent with the hypothesis that rising greenhouse gas concentrations in the troposphere trap heat that would otherwise radiate out to space through the stratosphere. Climate models predict this pattern, “thermal structure,” or “greenhouse fingerprint,” and observations confirm it.
The UAH V.6 record, however, not only shows little if any warming in the troposphere since 1996, it also shows little if any cooling in the stratosphere.
Figure explanation: Monthly global-average temperature variations for the lower troposphere, mid-troposphere, tropopause level, and lower stratosphere, 1979 through March 2015.
The absence of both tropospheric warming and stratospheric cooling since 1996 is remarkable considering that more than 31% of all industrial CO2 emissions since 1750 occurred during the past 18 years.
Fourth, although past is not always prologue, if the trend in the UAH V.6 dataset continues, 21st century warming should be limited to about one degree Celsius. At a minimum, the anemic warming of the past 36 years casts doubt on the big, scary warming projections popularized by the IPCC.