Our research has raised several issues on the robustness of the global surface temperature trend analyses. I am summarizing the questions raised over the last several months in this weblog, along with brief peer reviewed background material where available. Other weblogs, such as RealClimate.org, are invited to respond to these questions.
The first overarching question, of course, is what is meant by the âglobal average surface temperatureâ?? The 2005 National Research Council Report (see page 19 and page 21) provides a definition as
âAccording to the radiative-convective equilibrium concept, the equation for determining global average surface temperature of the planet is
dH/dt = f – T’/lamda (1-1)
where H…….is the heat content of the land-ocean-atmosphere system ……. Equation 1-1 describes the change in the heat content where f is the radiative forcing at the tropopause, Tâ² is the change in surface temperature in response to a change in heat content, and Î» is the climate feedback parameter (Schneider and Dickinson, 1974), also known as the climate sensitivity parameter, which denotes the rate at which the climate system returns the added forcing to space as infrared radiation or as reflected solar radiation (by changes in clouds, ice and snow, etc.).â?
Thus T is the âglobal average surface temperature â?. However, where is this temperature and its change with time, T’, diagnosed?”
Question: What is the level at which this temperature is monitored? Is Tâ height invariant near the surface, if the lowest levels of the atmosphere are used to compute Tâ?
Using the near surface air temperature changes as the climate metric to assess T’ raises the research questions listed below:
1. We have shown that the Parker Nature study entitled âLarge-scale warming is not urban” has serious issues on its conclusions, as well as demonstrated that an unrecognized until now warm bias occurs in nighttime minimum temperatures ( see 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?”)
Question: What is the magnitude of this bias in the analyses of the global surface temperature trends?
2. There are photographed major problems with the microclimate exposure of a subset of surface observation sites ( see Davey, C.A., and R.A. Pielke Sr., 2005: “Microclimate exposures of surface-based weather stations – implications for the assessment of long-term temperature trends”.
Question: What photographic documentation is available for the global network of surface temperature sites used to construct the long term global surface temperature analyses?
3. We have shown that surface air water vapor changes over time must be accounted for in the assessment of long term surface air temperature trends (see Pielke Sr., R.A., C. Davey, and J. Morgan, 2004: Assessing “global warming” with surface heat content” and Davey,
C.A., R.A. Pielke Sr., and K.P. Gallo, 2005: Differences between near-surface equivalent temperature and temperature trends for the eastern United States – Equivalent temperature as an alternative measure of heat content.”
Question: What are the quantitative trends in surface absolute humidity for the sites used to construct the global surface temperature trends, and what is the uncertainty that is introduced if this information is not available?
4. Our research has raised issues with the robustness of the adjustments that are used to âhomogenizeâ? surface temperature data. This includes adjustments made due to the time of observation, a change of instrument, the change in location, and from urbanization. Pielke Sr., R.A., T. Stohlgren, L. Schell, W. Parton, N. Doesken, K. Redmond, J. Moeny, T. McKee, and T.G.F. Kittel, 2002: Problems in evaluating regional and local trends in temperature: An example from eastern Colorado”
Question: What are the quantitative uncertainties introduced from each step of the homogenization adjustment? Do they vary geographically?
5. As discussed in the weblog of December 16, 2005 the raw surface temperature data from which global surface temperature trend analyses are derived are essentially the same. The best estimate we have seen is that 90-95% of the raw data is the same. That the four analyses produce similar trends should come as no surprise.
Question: What is the degree of overlap in the data sets that are used to construct the global average surface temperature trend analyses? To frame this question another way, what raw surface temperature data is used in each analysis that is not used in the other analyses?
These are important scientific questions which have either been poorly, or not at all, examined in climate assessments such as the IPCC and CCSP reports. Clearly, we need to move beyond such assessments that are written by individuals who are mostly evaluating their own research. Policymakers are poorly served by this inbred assessment framework by the scientific community.