Rearranging The Deckchairs

Frank O'Dwyer's blog

How to Falsify IPCC AR4 Trend Projections

Simply make up a high trend, and see if you can ‘connect’ it to information reported in IPCC AR4. Just a word or number in common may be sufficient to fool some ‘sceptics’. Lucia shows how it is done:

a trend equal to exactly 0.2 C/decade falls outside the ±95% confidence intervals for the trend consistent with the NOAA/NCDC data observations.


Quite often, if we chose a confidence level of 95%, the result of a statistical analysis guides us to conclude a trend that we can connect to information reported in the IPCC AR4 is found to be is false. (For example, the trend of 0.2C/century is diagnosed as false above.)

But a trend of ”exactly 0.2C/decade” cannot be connected to information reported in IPCC AR4. That document refers to a trend of ”about 0.2C/decade”. From AR4, Section 3

For the next two decades a warming of about 0.2°C per decade is projected for a range of SRES emissions scenarios. Even if the concentrations of all GHGs and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected. Afterwards, temperature projections increasingly depend on specific emissions scenarios (Figure 3.2).

There are no doubt many reasonable interpretations of “about” but “exactly” isn’t one of them. Of course this was pointed out to Lucia yonks ago.