The Global Average Surface Temperature Warming Really Is Overstated

There have been a remarkable amount of (deliberate?) misunderstanding regarding our new paper

Klotzbach, P.J., R.A. Pielke Sr., R.A. Pielke Jr., J.R. Christy, and R.T. McNider, 2009: An alternative explanation for differential temperature trends at the surface and in the lower troposphere. J. Geophys. Res., in press.

Examples of  misunderstanding in the blogosphere (as reported on Roger Pielke Jr.’s Blog)   include:

For those who are open-minded on this issue, I have summarized the findings below.

The Klotzbach et al paper examined if other real world data are consistent with the conclusion from our earlier papers;

“[F]rom our papers (Pielke and Matsui 2005 and Lin et al. 2007), a conservative estimate of the warm bias resulting from measuring the temperature near the ground is around 0.21 C per decade (with the nightime T(min) contributing a large part of this bias) . Since land covers about 29% of the Earth’s surface (see), the warm bias due to this influence explains about 30% of the IPCC estimate of global warming. In other words, consideration of the bias in temperature would reduce the IPCC trend to about 0.14 degrees C per decade, still a warming, but not as large as indicated by the IPCC”

This finding is based on observed temperature trends at two levels. While it is certainly a limited set of data, the theoretical basis for this conclusion, based on boundary layer physics is solid (see als0) .

The Klotozbach et al paper used data from both the surface and tropospheric analyses to further explore this issue. If the finding we made in Lin et al 2007 is robust than the following two hypotheses should be false;

1) If there is no warm bias in the surface temperature trends, then there should not be an increasing divergence with time between the lower troposphere and surface temperature anomalies. The difference between lower troposphere and surface temperature anomalies should not be greater over land areas.
2) If there is no warm bias in the surface temperature trends then the divergence should not be larger for both maximum and minimum temperatures at high latitude land locations in the winter.

Both were falsified. This provides significant further support to our conclusion that the monitoring (and predicting with multi-decadal global models) the temperature at a single level over land near the surface, as representative of deeper layer temperature trends that are positive, introduces a significant warm bias. Until further analysis is completed using temperature trend data at two or more levels near the surface, the best estimate that we have is that this warm bias  explains about 30% of the IPCC estimate of global warming [based on a global average surface temperature trend].


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