Models and Temperatures.

by Anthony Cox

There have been some interesting exchanges on Facebook recently. Shea Lewis, who is good value, went to the trouble of graphing the RSS tropical temperature record compared with the Coupled Model Intercomparison Project [CMIP 3]. CMIP 3 is an ensemble of temperature results produced by a number of Global Climate Models [GCM]. CMIP 3 was used as the basis for the fourth IPCC report, AR4. The graph below shows the CMIP 3 results compared with the official land based temperature indices:

The grey area is the range of results from all the GCMs taken to a 95% deviation; the wide range is because the assumptions about all the climate variables are tested in different combinations in the CMIP 3 GCMs. The black line is the mean of the ensemble results and the land based temperatures are in colour.

At first glance it looks as though there is a reasonable match. But it must be understood that no one CMIP 3 GCM necessarily achieved the black mean; the range of results is a spread of over 0.5ºC above and below that mean. So the overall range of uncertainty of the climate models of over 1ºC exceeds the entire observed warming during the 20th Century by at least 30%!

Then the fact that the land-based temperature indices have been mired in controversy about their adjustment procedures and results must be considered. Steve Goddard provides a great example of how these adjustments can increase the temperature trend here. Warwick Hughes provides another example for Melbourne here. It is obvious that the land based temperatures have been tainted by a warming bias so the at least 30% overreach for CMIP 3 is likely to be much higher.

How much higher can be seen by Shea’s graph of the Tropics based on RSS, one of the satellite temperatures and therefore arguably the most reliable of the temperature indices:

Shea’s graph shows CMIP 3 in yellow with RSS in black and the various trends shown including red from 1994, which has a trend of-0.009C or cooling.

That’s right, cooling. As CMIP 3 wanders off into an imagined hot future the reality is the opposite. Shea’s final, self-explanatory graph shows this starkly:

Use has been made of data from Remote Sensing Systems in the preparation of this opinion piece. AMSR-E data are produced by Remote Sensing Systems and sponsored by the NASA Earth Science.

MEaSUREs DISCOVER Project and the AMSR-E Science Team. 
Data are available at