Kevin “Travesty” Trenberth had a peer-reviewed article in Science entitled, “Has there been a hiatus? Internal climate variability masks climate-warming trends.”
First, the word “hiatus” is wrong. Using it assumes what it seeks to prove: that the atmosphere is warming substantially because of human activity. We do not know this is true; and given model results, an area where Trenberth treds oh so lightly, it is almost surely false. The word “hiatus” implies the warming is there, but has been “masked” or “beaten down” by other causes such that the total cause is a no-warming signal in the (operationally defined) global mean surface temperature (GMST).
The real question of interest is not whether there was a “hiatus” but what are the main causes of the (value of the) GMST? Some of the causes Trenberth mentions are uncontroversial; for instance, volcanic eruptions, which block incoming solar radiation. But one cause he mentions, and which is says is responsible for the “hiatus”, is not a cause at all. This is the Pacific Decadal Oscillation (PDO).
He says, “Observations and models show that the PDO is a key player in the two recent hiatus periods”. He cliams the PDO is responsible for “interannual variability” of the atmosphere. This cannot be so. The PDO is an effect, an observation. It is not a primary cause. The PDO is not something apart from the atmosphere, independent of it and which only shows up every so often. It is a pattern formed in the atmosphere by the same (and other) causes which are responsible for the GMST value.
And the same is true, of course, for the El Nino, La Nina, AMO, and any other human-identified handy pattern. To say the PDO is a cause is like saying the “pattern” of colder temperatures we notice in December in the northern hemisphere are responsible for (a.k.a. cause) winter.
Trenberth skirts around the lack of skill exhibited by climate models and implies the models would have been right—which means he acknowledges they were wrong—had this nasty PDO not had its way with the atmosphere. Such faith. He says, “the associated changes in the atmospheric circulation are mostly not from anthropogenic climate change but rather reflect large natural variability on decadal time scales. The latter has limited predictability and may be underrepresented in many models”.
This is silly. The models claimed to be able to identify the main causes of atmospheric change. Because the predictions were so awful is proof that this claim is false. We do not know all the main causes of atmospheric change. If we did, our forecasts would have been accurate.
As I said, the main causes of the changes in the atmosphere also cause changes in the man-identified pattern we call the PDO. We also do not do a stellar job of predicting the PDO. More evidence we do not understand all the causes of the changes in the atmosphere.
Further, there is no such thing as “natural variability”. It doesn’t exist like volcanoes and even human carbon dioxide emissions do. Natural variability is a measure, the result of us holding up a sort of yardstick to the atmosphere. The yardstick exists all right, but it has no causal influence of the atmosphere itself.
For being a world-renowned expert on our climate, Trenberth certainly speaks poorly of its operation.
Small points: Trenberth ignores the satellite data temperature record and instead relies on a statistical reconstruction which does not show the uncertainty in its estimates. He smooths his “data” to show us black lines which are not the “data”, and then speaks of these lines as he speaks of “natural variability”, i.e. as if it’s something real. And then he does some odd ad hoc piece-wise linear regression the purpose of which is unclear and, as far as I can tell, is of no use whatsoever, i.e. it makes no predictions like all good statistical models should.