by Judith Curry
A comprehensive history of the controversy surrounding tropospheric temperature trends has recently been published in WIRES Climate Change (h/t WUWT and Lorne LeClerc).
Tropospheric temperature trends: history of an ongoing controversy
Peter W. Thorne, John R. Lanzante, Thomas C. Peterson, Dian J. Seidel and Keith P. Shine
Changes in atmospheric temperature have a particular importance in climate
research because climate models consistently predict a distinctive vertical profile
of trends. With increasing greenhouse gas concentrations, the surface and
troposphere are consistently projected to warm, with an enhancement of that
warming in the tropical upper troposphere. Hence, attempts to detect this distinct ‘fingerprint’ have been a focus for observational studies. The topic acquired heightened importance following the 1990 publication of an analysis of satellite data which challenged the reality of the projected tropospheric warming. This review documents the evolution over the last four decades of understanding of tropospheric temperature trends and their likely causes. Particular focus is given to the difficulty of producing homogenized datasets, with which to derive trends, from both radiosonde and satellite observing systems, because of the many systematic changes over time. The value of multiple independent analyses is demonstrated. Paralleling developments in observational datasets, increased computer power and improved understanding of climate forcing mechanisms have led to refined estimates of temperature trends from a wide range of climate models and a better understanding of internal variability. It is concluded that there is no reasonable evidence of a fundamental disagreement between tropospheric temperature trends from models and observations when uncertainties in both are treated comprehensively.
WIRES Climate Change, Vol 2 Jan/Feb 2011 full paper link [here]
The debate surrounding tropospheric temperature trends, and the disagreement among different datasets and with models, has often been at the heart of the scientific debate surrounding AGW. Climate models predict a warming in the tropical upper troposphere, whereas the observational data sets have not.
In the 1990’s, there was academic “blood on the floor” over the discrepancies between the radiosonde analyses and the UAH satellite analyses. I became interested in this topic during the period that I served on NOAA’s Council on Long Term Climate Monitoring. We heard endless reports from Tom Karl and Dian Seidel on what they were doing to “massage” and interpret the radiosonde data. I was most unimpressed with what was going on in this analysis, and was motivated by this to write my only paper on this topic.
I revisited this topic circa 2005 when I served on the review committee evaluating the CCSP Synthesis and Assessment Report on Temperature Trends in the Lower Troposphere: Steps for Understanding and Reconciling Differences. Our first evaluation told them to work harder to sort out the differences between the two main satellite estimates. This actually happened, and an error was found in one of the data sets that substantially reduced the discrepancies.
I haven’t paid too much attention to this topic in recent years, but remain very interested in the issues surrounding the tropical upper troposphere.
The Thorne et al. paper is very comprehensive, clearly written, and well referenced. The main reason I find this paper to be of particular interest is the historical aspect of the treatment of uncertainty surrounding this topic. During the first decade, it was a case of I am right and the other dudes are wrong. Uncertainty assessment or even acknowledgement was pretty much absent.
In the Thorne et al. paper, the conclusion states:
The state of the observational and model sci- ence has progressed considerably since 1990. The uncertainty of both models and observations is currently wide enough, and the agreement in trends close enough, to support a finding of no fundamental discrepancy between the observations and model estimates throughout the tropospheric column. However, the controversy will undoubtedly continue because some estimates of tropospheric warming since 1979 are less than estimates of surface warming, or fall out- side of the range of analogous model estimates (e.g., Figure 8).
There are several key lessons for the future:
1. No matter how august the responsible research group, one version of a dataset cannot give a measure of the structural uncertainty inherent in the information.
2. A full measure of both observational uncertainty and model uncertainty must be taken into consideration when assessing whether there is agreement or disagreement between theory (as represented by models) and reality (as represented by observations).
3. In addition to better routine observations, underpinning reference observations are required to allow analysts to calibrate the data and unambiguously extract the true climate signal from the inevitable nonclimatic influences inherent in the routine observations.
I have two main reactions to this statement:
1. Finally, the community is paying attention to uncertainties, and beginning to understand that disagreement most likely implies uncertainty, rather than “I am right, the other dude is wrong.”
2. Whereas #1 is a good thing, the statement “The uncertainty of both models and observations is currently wide enough, and the agreement in trends close enough, to support a finding of no fundamental discrepancy between the observations and model estimates throughout the tropospheric column.” This statement is fine as along as this line of reasoning doesn’t travel along the path of assuming that the models and observations don’t disagree, and therefore we can have high confidence in the climate model results.
But it is really a good thing to see more awareness and realism in the community regarding uncertainties in both observations and models. The uncertainties highlight the need to actually understand the differences.