Tropospheric Humidity and CO2-Induced Global Warming
Paltridge, G., Arking, A. and Pook, M. 2009. Trends in middle- and upper-level tropospheric humidity from NCEP reanalysis data. Theoretical and Applied Climatology: 10.1007/s00704-009-0117-x.
The three researchers report that "the face-value 35-year trend in zonal-average annual-average specific humidity q is significantly negative at all altitudes above 850 hPa (roughly the top of the convective boundary layer) in the tropics and southern midlatitudes and at altitudes above 600 hPa in the northern midlatitudes." As a result, Paltridge et al. conclude that "negative trends in q as found in the NCEP data would imply that long-term water vapor feedback is negative - that it would reduce rather than amplify the response of the climate system to external forcing such as that from increasing atmospheric CO2." The ultimate outcome of this dilemma must therefore await a thorough study of the reliability of the pertinent NCEP data, in order to establish, in the words of the three scientists, "what (if any) aspects of the observed [humidity] trends survive detailed examination of the impact of past changes of radiosonde instrumentation and protocol within the various international networks" that collected the globe-spanning data that comprise the NCEP reanalysis archive.