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A New Temperature Trend of the Lower Troposphere Derived from Reanalysis Data
Reference
Bengtsson, L., Hagemann, S. and Hodges, K.E.  2004.  Can climate trends be calculated from reanalysis data?  Journal of Geophysical Research 109: 10.1029/2004JD004536.

What was done
The authors used the European Centre for Medium-Range Weather Forecasts' 40-year reanalysis (ERA40) data set, which is described by Simmons and Gibson (2000), to calculate the temperature of the lower troposphere (TLT) for the period 1979-2001, in order to compare the result with the lower tropospheric temperature record obtained from the Microwave Sounding Unit (MSU) observations of Christy et al. (2003) over the same time period.

What was learned
Although they had reason to believe that their final result was somewhat "on the high side," the authors report that the ERA40 TLT trend of +0.11°C/decade "is in agreement with Christy et al. (2003) but much smaller than the recent findings by Vinnikov and Grody (2003), who suggest that the TLT trend is +0.22 to +0.26°C/decade and thus closer to the IPCC results for the near surface temperature trend."

What it means
Controversy continues to swirl about the true rate of lower tropospheric and near-surface air temperature change over the past quarter-century, with multiple major studies both agreeing with and differing from the standard climate-alarmist contention that the earth experienced unprecedented warming over that time period.  Bengtsson et al. say their study "stresses the difficulties in detecting long term trends in the atmosphere," and they conclude that additional "major efforts along the lines indicated [in their study] are urgently needed" to help resolve the issue, which appears to be almost intractable.

References
Christy, J.R., Spencer, R.W., Norris, W.B., Braswell, W. and Parker, D.E.  2003.  Error estimates of version 5.0 of MSU-AMSU bulk atmospheric temperatures.  Journal of Atmospheric and Oceanic Technology 20: 613-129.

Simmons, A.J. and Gibson, J.K.  2000.  The ERA-40 Project Plan, ERA-40 Project Rep. Ser., 1.  European Centre for Medium-Range Weather Forecasts, Reading, United Kingdom.

Vinnikov, K.Y. and Grody, N.C.  2003.  Global warming trend of mean tropospheric temperature observed by satellites.  Science 302: 269-272.


Reviewed 21 July 2004