Summary: In February 2014 I examined surveys of climate scientists and found (as had others) that they showed broad agreement with the IPCC’s headline statement about warming since 1950. However time brings new research, such as a major survey that digs deeper and finds that only a minority of climate scientists agree with the full key statement of AR5 about greenhouse gases — the most recent IPCC report. That’s important news. Also see the important update below.
Update: fame from Politifact!
The good liberals at Politifact did a hit piece on this post, with skilled disinformation provided with the assistance of climate warriors in academia. It’s an interesting story of noble lie corruption, which I describe in
This post produced quite a frenzy among the alarmists. Linda Qiu at Politifact published a bizarre rebuttal, ignoring what I said and replying to things I didn’t say (this is a favorite tactic of alarmists). She recruited professors to do so, because science! For details see Politifact tells us about American politics and science. We should listen.
The Survey: finding the consensus
In March – April 2012 the PBL Netherlands Climate Assessment Agency, with several other scientists, conducted a survey of approximately 6,550 scientists studying climate change. It was published as “Scientists’ Views about Attribution of Global Warming” by Bart Verheggen et al in the 19 Aug 2014 issue of Environmental Science and Technology (peer-reviewed). In April 2015 they published a more detailed report (used in this post).
This survey covered many of the frontiers of climate science. This post examines one the questions about the keynote statement of the IPCC’s most recent work at time of the study — Assessment Report 4 (AR4, published in 2007). {This is a correction from the original post, which looked at the headline statement of AR5, about all forcings}. From AR4’s Summary for Policy-makers:
“Most of the observed increase is global average temperature since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.”
In 2013 the IPCC published AR5, which repeated this finding — but on page 884, in Chapter 10 of WGI: “We conclude, consistent with Hegerl et al. (2007b) {i.e., chapter 9 of AR4}, that more than half of the observed increase in GMST {global mean surface temperature} from 1951 to 2010 is very likely due to the observed anthropogenic increase in GHG {greenhouse gas} concentrations.”
The PBL survey is the first I’ve seen to test agreement with both facets of these statements. First, how much of the global surface warming is caused by anthropogenic (human-caused) emissions of greenhouse gases? (Note AR5 referred to all factors; see “Details” below). Only 1,222 of 1,868 (64% of respondents) agreed with AR5 that the answer was over 50%. If we exclude the 164 (8.8%) “I don’t know” respondents, 72% agree with the IPCC. So far, so good.
Now for the second part of the statement: what is the certainty of this finding? That the IPCC gives these answers is one of its great strengths. Of the 1,222 respondents to the PBL survey who said that the anthropogenic contribution was over 50%, 797 (65%) said it was 95%+ certain (which the IPCC defines as “virtually certain” or “extremely likely”).
Those 797 respondents are 43% of all 1,868 respondents (47% excluding the “don’t know” group). The PBL survey finds that only a minority (a large minority) of climate scientists agree with the AR4 keynote statement {and the similar finding in AR5’s chapter 10} at the 95% level typically required for science and public policy {Note: the last section added for greater clarity}.
Update: reconciling the PBL survey results with AR4 & AR5
Tom Curtis (attorney) posted a comment at Skeptical Science, that put the PBL survey results in the proper context of AR4 and AR5. Kudos to him for this excellent work!
From AR4’s Summary for Policy-makers: “Most of the observed increase is global average temperature since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.” Published in 2007, this reflected the consensus at that time.
In 2013 the IPCC published AR5, which repeated this finding — but on page 884, in Chapter 10 of WGI: “We conclude, consistent with Hegerl et al. (2007b) {i.e., chapter 9 of AR4}, that more than half of the observed increase in GMST {global mean surface temperature} from 1951 to 2010 is very likely due to the observed anthropogenic increase in GHG {greenhouse gas} concentrations.”
GHG being, of course the focus of proposed public policy changes to mitigate climate change.
AR5 shifted the headline SPM finding to “extremely likely” about “all anthropogenic forcings”. This was widely but mistakenly reported as an increase in their confidence level about anthropogenic warming. Even some (many?) climate scientists believed that the IPCC had increased its confidence level about anthropogenic forcings from AR4 to AR5 (e.g., this interiew with Prof Judith Curry).
Conclusions
Scientists, like experts of all kinds, often say they “just know” things for which there is uncertain or contradictory research. A massive body of research shows that such opinions are often wrong. That’s why we rely on the power of science to give more reliable answers, and on organizations like the IPCC to help us understand the current state of knowledge about climate change. The IPCC is a political entity, but it is the best we have.
But the challenge of climate change — and the trillions it will cost to mitigate — require a clear view of what’s known, with what degree of certainty. But instead we’ve been told increasingly fanciful tales of what “97% of climate scientists” believe, often things far beyond the most confident statements in the IPCC’s AR5.
This latest survey suggests that even the IPCC might not represent the consensus as accurately as previous surveys research indicated. Only 64% of climate scientists agreed that over half of the warming since 1950 was from anthropogenic factors, and only 65% of those had a confidence level of 95%+ — so that only 43% agree with the full keynote statement of AR5. That’s important by itself, and tells us much about the accuracy of what we read in the news media about climate science.
Many scientists have warned us of this problem.
“The drive to reduce scientific uncertainty in support of precautionary and optimal decision making strategies regarding CO2 mitigation has arguably resulted in unwarranted high confidence in assessments of climate change attribution, sensitivity and projections…”
— “Climate Science and the Uncertainty Monster” by Judith Curry (Prof Atmospheric Science, GA Inst Tech), April 2015.
Also: Is there a minority viewpoint or theory in climate science?
The PBL survey shows substantial minority viewpoints in the many specific questions they examine. The study does not look for patterns, to discover if there is one or more “skeptic” theories opposing the consensus — the dominant paradigm, to use Thomas Kuhn’s The Structure of Scientific Revolutions
Kuhn’s work shows that a paradigm cannot be disproved, only replaced (details here). Unless the skeptics form a theory, they’ll remain minor players in the climate science debate. The public policy debate about climate change (they’re distinct, although often conflated) operates more like a court: the defense (take no action) wins if they raise a reasonable doubt about the threat of anthropogenic climate change (this was revised in response to a comment).
Note that preparing for occurrence of past extreme weather would help prepare us, and that should command support from both sides. I suspect it will continue to get support from neither side because politics rules.
For more about the two debates see this by political scientist Don Atkin: “There are two debates about climate change“.
Updates
(1) There are always messy details, so these numbers have to be interpreted broadly. In AR4 the keynote finding was that over half of the warming was caused by greenhouse gases — with 90% certainty. AR5 said the certainty was 95% for all anthropogenic forcings. This relevant question in the PBL survey referred only to greenhouse gases. The difference gets into some complex matters, explained in the EST paper under “Aerosol Cooling Versus GHG Warming”.
(2) A report confirming the findings reported here: “97 consensus? No! Global warming math, myths, and social proofs” by the Friends of Science, 17 February 2014. Thoroughly documented; 48 pages long.
(3) I suspect that the PBL study is a clear case of “p-hacking”, slowly emerging to view as a major problem in modern science. See this from the excellent “Psychology is in crisis” article at VOX.
Take Joseph Hilgard, a psychologist at the University of Pennsylvania. In a recent blog post titled “I was wrong,” he fesses up to adding a shoddy conclusion to the psychological literature (with the help of colleagues) while he was a graduate student at the University of Missouri. “[W]e ran a study, and the study told us nothing was going on,” he writes. “We shook the data a bit more until something slightly more newsworthy fell out of it.”
This a bold and honest move — the type that gives me reasons to be optimistic for the future of the science. He’s confessing to a practice called p-hacking, or the cherry-picking of data after an experiment is run in order to find a significant, publishable result. While this has been commonplace in psychology, researchers are now reckoning with the fact that p-hacks greatly increase the chances that their journals are filled with false positives. It’s p-hacks like the one Hilgard and his colleagues used that gave weight to a theory called ego depletion, the very foundation of which is now being called into question.
The authors of the PBL survey were looking to confirm the results of the AR4 headline statement about GHG (relegated to the footnotes in AR5, replaced by one about “all anthropogenic forcings”). They found that only 43% of all 1,868 respondents agreed at the 95% confidence level. They buried this result and shifted the emphasis to who agreed with it. Unfortunately their survey was not designed to elicit robust information about this. Exactly as described in the VOX article.
But there was a problem: The experiment found no effects for game violence or for game difficulty. “So what did we do?” Hilgard writes. “We needed some kind of effect to publish, so we reported an exploratory analysis, finding a moderated-mediation model that sounded plausible enough.” They found that if they ran the numbers accounting for a player’s experience level with video games, they could achieve a significant result. This newfound correlation was weak, the data was messy, and it barely touched the threshold of significance. But it was publishable. …
There are a few big problems with this. The biggest is that their experiment was not designed to study experience level as a main effect. If it had, they perhaps would have done a better job of recruiting participants with varying ranges of experience. “Only 25 people out of the sample of 238 met the post-hoc definition of ‘experienced player,'” Hilgard writes. Such a small sample leaves the study with much less statistical power to find a real result.
For More Information
If you liked this post, like us on Facebook and follow us on Twitter. For more information see The keys to understanding climate change and My posts about climate change. Also, see these posts about the IPCC…
- “Climate Change: what do we know about the IPCC?”, 2
- Climate scientists speak to us. What is their consensus opinion?
- The IPCC releases its advice on “Impacts, Adaptation and Vulnerability”. To be attacked from both sides.
- Another disturbing article about climate change. Fortunately we have the IPCC!
- Is our certain fate a coal-burning climate apocalypse? No!
To help you better understand today’s extreme weather
To learn more about the state of climate change see The Rightful Place of Science: Disasters and Climate Change
