Independently produced data sets that describe the four-dimensional temperature structure from the surface through the lower stratosphere provide different temperature trends. These differences are seen in varying degrees in comparisons of separate in-situ (surface and weather balloon) data sets, in comparisons of separate space-based data sets, and in comparisons of individual data sets drawn from the different observational platforms and different trend analysis teams. Recent efforts to address the uncertainties regarding the temperature structure of the lower atmosphere (i.e., from the surface through the lower stratosphere) have included release of a report under the auspices of the National Research Council entitled: “Reconciling Observations of Global Temperature Change” (National Academy Press, 2000) and the Third Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge University Press, 2001, pp 101-123). Although these documents provided a great deal of useful information, the complexities of the issue coupled with shortcomings of the available observing systems prevent resolution of a number of fundamental questions.

This CCSP synthesis product will address the accuracy and consistency of these temperature records and outline steps necessary to reconcile differences between individual data sets. Understanding exactly how and why there are differences in temperature trends reported by several analysis teams using differing observation systems and analysis methods represents a necessary step in reducing the uncertainties that underlie current efforts focused on the detection and quantification of surface and tropospheric temperature trends. Consequently, this synthesis product promises to be of significant value to decision makers, and to the expert scientific and stakeholder communities. For example, it is expected that this assessment will be a major contributor to the IPCC (2007) Climate Assessment. In addition, the information generated is expected to be used by the Global Climate Observing System Atmospheric Observation Panel to help identify effective ways to reduce observational uncertainty.

The paper will review the objectives of the synthesis report, the questions that are being addressed, who is involved, how to engage in the review process, and the linkages between the Synthesis product and the IPCC 2007 assessment on Climate Change.