A New Paper That Documents Biases and Uncertainties With Land Surface Temperature Trend Assessments

We have completed a new paper based on our presentation at the July 2006 Santa Fe Conference on Global Warming and the Next Ice Age.

Pielke Sr., R.A., C. Davey, D. Niyogi, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, J. Angel, R. Mahmood, S. Foster, J. Steinweg-Woods, R. Boyles , S. Fall, R.T. McNider, and P. Blanken, 2006: Unresolved issues with the assessment of multi-decadal global land surface temperature trends. J. Geophys. Research, submitted.

The abstract reads,

“The paper documents various unresolved issues in using surface temperature trends as a metric for assessing global and regional climate change. A series of examples ranging from errors caused by temperature measurements at a monitoring station to the undocumented biases in the regionally and globally averaged time series are provided. The issues are poorly understood or documented and relate to micrometeorological impacts due to warm bias in nighttime minimum temperatures, poor siting of the instrumentation, effect of winds as well as surface atmospheric water vapor content on temperature trends, the quantification of uncertainties in the homogenization of surface temperature data and the influence of land use/land-cover (LULC) change on surface temperature trends.

Due to the issues presented in this paper related to the analysis of multi-decadal surface temperature we recommend that greater, more complete, documentation and quantification of these issues be required for all observation stations that are intended to be used in such assessments. This is necessary for confidence in the actual observations of surface temperature variability and long-term trends.”

The paper has several section headings,

Definition of a Global Average Surface Temperature

Difficulties with the Use of Observed Nocturnal Warming Trends as a Measure of Climate Trends

Photographic Documentation of Poor Sitings

Influence of Trends in Surface Air Water Vapor Content on Temperature Trends

Uncertainties in the Homogenization of Surface Temperature Data.

Degree of Independence of Land-Surface Global Surface Temperature Analyses

Relationship Between In-situ Surface Temperature Observations and the Diagnosis of Surface Temperature Trends from Reanalyses

Influence of Land-Use/Land-Cover Change on Surface Temperature Trends

Our conclusion states,

“This paper identified a range of issues with the use of the existing land-surface temperature data to assess multi-decadal trends in surface air temperature. Since the analyses from such data is so important in national and international assessments of climate change [e.g. see CCSP, 2006 and National Research Council, 2005, Figures 1-4 http://darwin.nap.edu/books/0309095069/html/24.html), the issues that we discuss in this paper need to be evaluated in depth……

A major conclusion is that, as a climate metric to diagnose climate system heat changes (i.e., ‘global warming’), the surface temperature trend, especially if it includes the trend in nighttime temperature, is not the most suitable climate metric. As reported in Pielke [2003] the assessment of climate heat system changes should be performed using the more robust metric of ocean heat content changes rather than surface temperature trends. If temperature trends are to be retained in order to estimate large scale (including a global) average, the maximum temperature is a more appropriate metric than using the mean daily average temperature. This paper presents reasons why the surface temperature is inadequate to determine changes in the heat content of the Earth’s climate system.”

We welcome comments on this paper. It clearly documents that the reliance of setting climate policy based on a climate metric (the global surface average temperature) which has so many remaining uncertainties is not an accurate assessment measure of multi-decadal climate change and, therefore, is an inadequate linkage between science and policy.

The type of analyses that are presented in our paper should have been included in the CCSP Report “Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences“. Unfortunately, as I discuss in my Public Comment on CCSP Report, the CCSP Report failed to provide the appropriate beadth of perspectives that the policymakers need. That CCSP Report, therefore, is an advocacy document which promotes the narrower perspective of its authors on the subject of reconciling surface and tropospheric temperature trends. The JGR paper that we have completed should, therefore, be considered as adding information to be communicated to policymakers on the robustness of the multi-decadal surface temperature trends.

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