Error Identified by Urs Neu in one of my Interpretations of the Results in Lin et al. 2007

Urs Neu of the Forum of the Swiss Academy of Sciences has found a significant error in my follow-on interpretation of the results of our paper

Lin, X., R.A. Pielke Sr., K.G. Hubbard, K.C. Crawford, M. A. Shafer, and T. Matsui, 2007: An examination of 1997-2007 surface layer temperature trends at two heights in Oklahoma. Geophys. Res. Letts., 34, L24705, doi:10.1029/2007GL031652.

He and I have exchanged a number of e-mails over the past week or so, and I very much appreciate the patient, constructive interaction that we had on this paper.  The paper itself has a typographical error which led to my misinterpretation of the Lin et al. study in a follow on analysis that I completed.  The typographical error is in the y-axis of Figure 2a  (the labeling as the “absolute value of LR) and in the definition of the LR as the absolute magnitude of the lapse rate in paragraph 13.  The correct definition of LR as used in all of the analyses is given in paragraph 7.

The paper included the finding that for the time period June 1997 to May 2007 in Oklahoma

” a significant trend of about -0.21 ± 0.09°C ( per 10 m) per decade was discovered in the Oklahoma time series. The trend of daily nighttime lapse rate was about three times larger in magnitude than the trend of daily daytime lapse rate”

and that

Our results also indicate that the 1.5 or 2 m minimum long term temperature trends over land are not the same as the minimum long term temperatures at other heights within the surface boundary layer (e.g. 9 m), even over relatively flat landscapes such as Oklahoma.”

The raw data has been recomputed and confirms  that all of the results and findings presented in our paper are correct.  Thus the paper remains a robust contribution to the assessment of temperature trends at two levels.

However, based on our results of that paper, I incorrectly concluded from the Lin et al statement of a negative trend in lapse rate that

“Using the Lin et al. (2007) observational results, a conservative estimate of the warm bias resulting from measuring the temperature from a single level near the ground is around 0.21°C per decade (with the nighttime minimum temperature contributing a large part of this bias). Since land covers about 29% of the Earth’s surface, extrapolating this warm bias could explain about 30% of the IPCC estimate of global warming. In other words, consideration of the bias in temperature could reduce the IPCC trend to about 0.14°C per decade; still a warming, but not as large as indicated by the IPCC.”

The error in my interpretation was that I accepted (incorrectly) that the negative trend referred to the absolute value of the lapse rate. The lapse rate (confusingly) is defined as negative when the atmosphere has dT/dz > 0 and positive when dT/dz <0.

 The actual bias from the Lin et al. data under light winds at night is a cold bias.  The -0.46 +/- 0.29ºC per 10 meters per decade in Figure 3e means that the lapse rate at night became steeper.  If this bias was representative of the land areas of the Earth, it would mean that the IPCC underestimated the magnitude of the IPCC estimate of global warming.

The Lin et al paper was cited in order to provide  observational support for the hypotheses  presented in

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.

The specific text related to Lin et al with respect to a warm bias, however, will be removed from the Klotzbach et al paper. Citing the paper, however, to document that measuring temperatures at one level near the surface introduces a bias (when the goal is to use that temperature measurement to diagnose global warming and cooling) will remain. This bias is particularly important when the winds are light and the surface boundary layer stably stratified. Urs and I did agree on this issue that the use of a temperature at one level to diagnose a  temperature trend through a deeper layer of the troposphere can introduce a bias.

The conclusions in

Pielke Sr., R.A., and T. Matsui, 2005: Should light wind and windy nights have the same temperature trends at individual levels even if the boundary layer averaged heat content change is the same? Geophys. Res. Letts., 32, No. 21, L21813, 10.1029/2005GL024407

and

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.

are not affected by the error in my interpretation on the lapse rate trend. The Lin et al. paper was introduced as the only example we are aware of in which long term trends of temperatures at two levels are assessed. While the data was only for the period June 1997 to May 2007, and just for Okalahoma, it does provide insight into this issue. We need more such data analyses, including over high latitude continental areas in the winter, in order to further test our hypothesis.

In summary, the error in my interpretation of the Lin et al lapse rate trends does not alter the conclusions in Pielke and Matsui 2007 and Klotzbach et al. 2009. We present scientific evidence that any effect which reduces the slope of the vertical  temperature profile within a stably stratified surface boundary layer will introduce a warm bias, while any process that increases the magnitude of the slope of the vertical  temperature profile in a stably stratified surface boundary layer will introduce a cool bias, remains a robust finding based on boundary layer dynamics.

The Klotzbach et al. 2009 results indicates that in recent years it is the warm bias that dominates.

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