Earlier this year, Greg Hollin and Warren Pearce published a short letter in Nature Climate Change entitled Tension between scientific certainty and meaning complicates communication of IPCC reports.
In contrast to their claims, we demonstrate in our comment on this article that the IPCC correctly placed the hottest decade in the context of long-term trends. The IPCC did not dismiss the recent slowdown in surface warming, the so-called “hiatus” or “pause”, as scientifically irrelevant.
Hollin and Pearce’s central premise is nicely encapsulated in the abstract of their paper:
Here we demonstrate that speakers at the press conference for the publication of the IPCC’s Fifth Assessment Report (Working Group 1) attempted to make the documented level of certainty of anthropogenic global warming (AGW) more meaningful to the public. Speakers attempted to communicate this through reference to short-term temperature increases. However, when journalists enquired about the similarly short ‘pause’ in global temperature increase, the speakers dismissed the relevance of such timescales, thus becoming incoherent as to ‘what counts’ as scientific evidence for AGW.
This observation leads them to theorize about the tension between scientific certainty and meaning. But did they actually demonstrate what they claimed they did? We argue in a comment to this article that they did not.
They base their statement that IPCC speakers attempted to communicate ‘meaning’ by reference to short-term temperature increases on this statement made by Pachauri:
the decade 2001 onwards having been the hottest, the warmest that we have seen
This statement was explicitly placed in the context of long-term, climatically relevant trends, as indicated by Pachauri’s preceding words and the graph below (IPCC AR5 SPM fig 1) that was prominently shown at the press conference:
each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850
That is an entirely different ballgame than the short-term variability that underlies the slowdown of the surface warming trend (often referred to as “the pause”). So no, they did not demonstrate in the least that IPCC speakers “relied on temporally local events to increase public meaning”. Hollin and Pearce’s premise is based on misunderstanding the timescales that were discussed.
What about the claim that IPCC speakers dismissed the relevance of the so-called “pause”?
As we write in our comment, five of the 18 journalists asked a question about recent temperature trends; none were ignored. Also David Rose’s question, which is featured prominently in Hollin and Pearce’s argument, was not dismissed. Stocker responded to Rose’s question, followed by Jarraud explaining why he regarded it as “ill-‐posed”, reframing it as a well-posed question, and responding to that. See the (freely available) Supplemental Information for more details.
So no, Hollin and Pearce did not demonstrate that the relevance of the slowdown was dismissed. Hotwhopper hammers home this and related points with lots of extra detail, showing that the IPCC message was clearly received by most journalists and that only one journalist who asked a question at the press conference “condemned” the IPCC for supposed dismissal. This journalist, as you might suspect, was David Rose, for whom IPCC bashing is a modus operandi.
The entire premise for their argument thus seems to rest on shaky ground. Their conclusions about e.g. the IPCC’s credibility being somehow eroded by their (in Hollin and Pearce’s eyes) mixed messages are thus not supported.
I’m actually surprised that in their reply to our comment, Hollin and Pearce don’t acknowledge their mistaken interpretation regarding timescales, but rather keep digging their heels in regarding that point. E.g. they reiterate that Pachauri’s quote above was “illustrative of references to the warmest decade made by all three speakers”, apparently without realizing, or not considering it as relevant, that this and other such references were made in the context of the long-term trend. Very peculiar.
They wrote a blogpost in which they try to reflect on the meaning of this back and forth in the scientific literature. It’s an interesting read, and they basically argue that their initial letter was based on inductive research: starting with the data, seeing patterns or interesting things, and the theories and broader claims are integrated later. They claim that this is more common in qualitative social science than it is in natural science and that this difference may be at the root of our disagreement. I’m actually quite comfortable with such inductive style research. I have often started my research by looking at “what the data told me” as my PhD advisor used to say, especially for a large body of field observations. That was also the approach we took in analyzing the data from our climate science survey.
And Then There’s Physics, also co-author of the response to Hollin and Pearce, goes into more detail on this point, and rightly wonders
why it makes any difference whether one’s approach is inductive or deductive. What you present should be a reasonable representation of reality, whether you approached it inductively (“the data looks interesting, why is that?”) or deductively (“I have a theory/hypothesis, let me collect some data to test it”). For example, either the IPCC fell into a trap by using one indicator to stress the certainty of AGW while dismissing another essentially equivalent indicator, or they didn’t; either the IPCC dismissed the so-called “pause”, or they didn’t. It can’t really be both.
I would hardly think that the difference in interpretation between Hollin and Pearce on the one side and Jacobs et al (myself included, but also e.g. cognitive psychologist Stephan Lewandowsky) on the other side boils down to a typical difference in approach between social science and natural science. Rather, it boils down to the former misinterpreting statements relating to timescales and basing the whole remainder of their argument on a false premise.
Update (27 Oct 2015)