The Climate Science website has discussed the lack of skill in multi-decadal climate predictions (e.g. see). This weblog extracts information from the CCSP Report “Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differencesâ?, and an associated news report, which further confirms the level of ability of the multi-decadal global climate models in providing skillful reconstructions of the surface and tropospheric temperature trends over the last few decades using the global models forced by prescribed climate forcings (which, of course, is a time period when we have observed data).
A necessary, although not a sufficient, test of potential skill for the future decades is that the least several decades be accurately predicted.
As given in a summary of the CCSP Report, the news report by Richard Kerr in the May 12, 2006 issue of Science, entitled, âNo Doubt About It, the World is Warmingâ? (subscription required) includes the text,
“The report authors found that over the 25-year satellite record, the surface and the midtroposphere each warmed roughly 0.15Â°C per decade averaged over the globe, give or take 0.05Â°C or so per decade. The tropics proved to be an exception: The models called for more warming aloft than at the surface lately, whereas most observations showed the reverse. Reconciling that discrepancy will have to wait for the next round of synthesis and assessment.â?
The CCSP claims that the global models can skillfully predict global average surface and tropospheric temperature trends, yet they cannot skillfully predict tropical zonally averaged surface and tropospheric temperature trends. The significance of this admission is, unfortunately, not pursued. A skillful global average cannot be achieved if a significant portion of the globe (the tropics) is not skillfully predicted!
Second, from page 145 of the 2006 Response to the Public Comment of the CCSP Report âSynthesis and Assessment Product 1.1 âTemperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differencesâ?,
âOwing to natural internal variability, models cannot be expected to reproduce regional patterns of trend over a period as short as 20 years from changes of radiative forcings alone.â?
Thus, even the CCSP Committee accepted that regional predictive skill can not be attained for periods of two decades. The Report is silent on what time period skillful regional predictions of surface and tropospheric trends can be achieved, but it is clearly longer than 20 year time frames.
A very significant conclusion from the CCSP Report, therefore, is that the multi-decadal global climate predictions have demonstrated NO skill at predicting regional surface and tropospheric temperature trends. This is a major conclusion from the Report, even if the Committee chose not to mention it. Thus the application of the multi-decadal global climate models to regional projections in the 21st century for surface and tropospheric temperatures are not scientifically sound. Moreover, if the models cannot skillfully predict temperature, the much more difficult climate variables such as precipitation certainly should not be provided to the impact community or to policymakers as skillful projections.