The IPCC Is Never Wrong -1- Why Kevin Trenberth Is Right

Thus spoke Dr Kevin E Trenberth, Head of the Climate Analysis Section at the National Center for Atmospheric Research in the (very welcome!) Gray/Trenberth written debate hosted by the Tea Party of Northern Colorado:

I have found that the only scientists who disagree with the IPCC report are those who have not read it and are poorly informed

Contrarily to what the most argument-challenged readers of this blog might think, I fully agree with Dr Trenberth’s statement. Only, I arrive at his same conclusion starting from a very different point of view (wonder if Morano will ever try to sing a different tune?).


I have read several chapters of the IPCC AR4 (2007) (sadly, I have not read the whole thing in full from start to end and seriously wonder if anybody ever has). Fact is, they are all written in a scientifically very valid way. As the science of climate is still full of uncertainties, then whatever the future, may it be hot, may it be cold, it will be impossible to ever find in the IPCC reports any item that may be actually considered as fundamentally wrong or misleading.

Everything is in there and its opposite, by wise [UPDATE: “wise” means “wise” in a POSITIVE way…do not mix it up with “weasel” or anything else with a bad connotation] use of words like “could”, “might” and “likely”. Even if we meet again in 2050 and global cooling is in full swing, still the IPCC reports will be, in a sense, correct. Take for example AR4-SYR-SPM (Synthesis Report, Summary for Policymakers)

page 5: Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations

page 7: Continued GHG emissions at or above current rates would [note how they had so many would‘s to distribute, they added one too many here] cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century

The meaning of “very likely” is explained in the box Treatment of uncertainty” in the Introduction of the Synthesis Report (page 27):

Where uncertainty in specific outcomes is assessed using expert judgment and statistical analysis of a body of evidence (e.g. observations or model results), then the following likelihood ranges are used to express the assessed probability of occurrence: virtually certain >99%; extremely likely >95%; very likely >90%; likely >66%; more likely than not > 50%; about as likely as not 33% to 66%; unlikely <33%; very unlikely <10%; extremely unlikely <5%; exceptionally unlikely <1%.

Since “very likely” stops at 90%, it means that the IPCC experts agree that there is a 10% probability that most of observed temperature increases might not be due to “increase in anthropogenic GHG concentrations“. And that there is a 10% probability that the 21st century will not see anything larger than the 20th century has seen.

So if anything like that actually happens, well, the IPCC AR4 has already included that possibility, has it not?

Interestingly, if the IPCC work were to be presented as a scientific article, and the p-value associated to the null hypothesis (that observed temperature increases have nothing to do with increased GHG concentrations) were 0.1 or 10%, most if not all journals would deny publication.