What’s the consensus of climate scientists? Why do we care?

Summary: Here’s a briefing about climate change, prepared for Politifact at their request. Unused, of course, since the reporter was just fishing for smears (here’s an analysis of what they published). However, it’s a useful introduction to this complex subject. What do we know about the consensus of climate scientists, and why does it matter? These are unedited emails, and so roughly written and unproofed.   {2nd of 2 posts today.}

Stories, better than science

Initial Inquiry by Linda Qiu of Politifact, and my response

I’m a reporter with PolitiFact, the fact-checking website of the Tampa Bay Times. I’m currently looking into something Rick Santorum said: 57% of scientists “don’t buy into the idea that CO2 is the knob that’s turning the climate.” His campaign hasn’t gotten back to me on his source but one of your posts also has the figure, but it’s not quite what Santorum said. So I was hoping for your take on Santorum’s reading on your analysis — how accurate is it?

I have a lot of data about this. Here’s a quick data dump. I’m in the middle of something about this very subject, so don’t have time to compose. Tell me what more you’d like. I can provide links and cites for all of this. I work late, so deadlines are not a problem.

There have been many surveys seeking to determine the consensus of scientists and the subgroup of climate scientists (neither group having a clear definition) about the headline attribution statements of the IPCC. That is, how much of the warming since 1950 is attributed to us.  The IPCC states its findings in two parts: the finding, and the IPCC’s confidence in that finding. The latter is off little relevance to science, but obviously of great importance when taking public policy action. For example, it’s nice to know that all scientists believe “X”, but what if they have little confidence in that belief?

The standard measure of confidence is 95% (defining what this means is both complex and controversial, especially now with the replication crisis). The IPCC defines 90%+ as “very likely” and 95%+ as “extremely likely”.

The first round of surveys concerned only the first part: how much of the warming is from us. Almost all scientists agree that there has been warming during the past 2 centuries; only the amount and cause is debated.  They found strong agreement with the IPCC finding (what that finding is I’ll discuss below).

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. This was imo excellent — the best survey on the subject done so far, by far. 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.  The first questions asked about the finding of the IPCC’s Fourth Assessment Report (AR4) in their 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.”  {The subject is important since proposed measures to reduce climate change {Obama’s Clean Power Plan} focus almost exclusively on reducing emissions of greenhouse gases.

The PBL survey found that only 64% of climate scientists responding agreed that over half of the warming since 1950 was from anthropogenic greenhouse gases (GHG) — a majority, but less than I (and others) expected).

PBL survey: question 1a

For the second part, only 65% of those had a confidence level of 95%+ — so that only 64% * 65% = 43% agree with the finding at the 95% level. If you lower the bar —  89.3% agree at the 90% level (not significant by the usual standards) — so 64% * 89% = 57% agree with the finding as stated in AR4 (more than half + very likely). It’s a majority, but not an impressive one compared to the scale of public policy action advocates recommended.

PBL survey: question 1b

Restated in absolute numbers, 797 respondents (43%) of the 6,550 people asked and 1,868 who responded (47% excluding the “don’t know” group) agreed at the 95% level.

The authors of the survey responded to the results by looking at the smaller numbers who self-reported publications — deeming high publication numbers to indicate “expertise”. I believe that’s a poor measure of expertise, and almost a “no true Scotsman” response. But that’s a separate discussion.

What about the AR5 (2013)? They changed the headline finding from about anthropogenic greenhouse gases to all anthropogenic forcings.  They reiterated their finding about GHG 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.”

This shift in subject of the headline finding confused almost everybody – journalists, amateurs, scientists — hence the widespread comment that the IPCC had increased its confidence in human-caused climate change. They hadn’t.

I hope this helps.  Additional information available on request.

Follow-up questions by Linda Qiu, and my response

I really appreciate you replying so quickly Larry! Two follow-ups.

1. Can you comment on Sen. Santorum’s reading of your analysis? He says: “The most recent survey of climate scientists said about 57 percent don’t agree with the idea that 95% of the change in the climate is caused by CO2 … There was a survey done of 1,800 scientists, and 57 percent said they don’t buy off on the idea that CO2 is the knob that’s turning the climate.”

2. Have you seen the survey author’s response to your post? Would love to hear your thoughts on that as well.

I’m glad to help.

(1)  The incredible immense complexity of climate change, both as a science and vital public policy issue, defies the soundbites the define modern American politics. Almost anything about climate change that is specific, understandable, brief and exciting is probably inaccurate. {response about Santorum omitted as off-topic here.}

(2)  I made several responses on that thread, before giving up. Science is often contentious. Politicized science freezes positions so that discussions often become like clashing blocks of wood.

Bart downplayed the surprising “headline” findings from question 1a and 1b, instead focusing on the results sorted by the self-reported number of publications — as a measure of expertise. I believe that’s not a useful measure of expertise, and undercut one of the most valuable aspects of the PBL survey — the breadth of the climate scientists in the sample. Some objections. —

  • The breadth of the survey included people from different fields who will have different rates of publication.
  • Quantity is not quality. Do a few major articles show less expertise than many publications in minor journals (even pay-to-play journals)?
  • More useful measures of expertise include education, job history, impact factors, and H-indexes.

Also, the survey probably included both academics and practitioners. Do the later have less expertise because they tend to publish less? There might be a difference of opinion between the two groups, tentatively suggested by “Meteorologists’ views about global warming: A survey of American Meteorological Society professional members“, Neil Stenhouse et al, Bulletin of the American Meteorological Society, July 2014. They found lower agreement with the IPCC headline findings among meteorologists than found in studies of climate scientists.

I believe Bart points to a fruitful subject for further research, but the PBL survey provides a weak basis for conclusions about scientists’ beliefs vs their expertise.

(3)  Sidenote: The comment I found most interesting was by Tom Curtis (attorney) at Skeptical Science, pointing out that AR4 and AR5 had the identical finding about greenhouse gases (in the Summary for policy-makers of AR4, buried on page 884 of AR5). I believe the authors didn’t know this. Judging from the quotes I’ve found, almost nobody did. I’m writing about this now.

This is one of the most fascinating aspects of climate change: some aspects of the material are poorly understood.  Another example: how many journalists pointed out that the IPCC finding about greenhouse gases — the foundation of Clean Power Plan — was at the 90%+ (“very likely”) level, below the usually required 95% level.  I doubt the FDA would approve a new flavor of aspirin (I’m dating myself here) with a 90% confidence level. Details here.

For More Information

See a report confirming the findings describe in this post: “97 consensus? No! Global warming math, myths, and social proofs” by the Friends of Science, 17 February 2014. Thoroughly documented; 48 pages long.

Please like us on Facebook, follow us on Twitter, and post your comments — because we value your participation. For more information about this vital issue see The keys to understanding climate change and My posts about climate change. Especially see these posts about the future of climate change…

To support the FM website project please hit the tip jar (on top of the right-side menu bar). Your help makes this possible.

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 by Roger Pielke Jr. (Prof of Environmental Studies at U of CO-Boulder, and Director of their Center for Science and Technology Policy Research).

The Rightful Place of Science: Disasters and Climate Change
Available at Amazon.

22 thoughts on “What’s the consensus of climate scientists? Why do we care?

    1. Joan,

      The Factcheck article is even less accurate than the Politifact. I’ll give two obvious errors.

      “At the time of the survey, the IPCC’s official position — as stated in the Fourth Assessment Report — was that it was “very likely” (greater than 90 percent probability) that GHGs had caused most of the warming. That assessment was only upgraded to “extremely likely” in the report released in 2013.”

      (1) That’s quite false. The finding about greenhouse gases was identical (“very likely”) in both AR4 and AR5 (I quoted both in my original post, and in this one). The finding in AR5 of “extremely likely” was about all anthropogenic forcing. it was not an “upgrade”, as AR4 had nothing like it.

      (2) The almost universal test for significance in both science and public policy is at the 95% level. Hence I looked for agreement with the finding (more than half of warming since 1950 due to anthro GHG) at the 95% level. Note that all these people know this quite well. They are attempting to deceive you. Successfully, I suspect.

      I could continue, but there’s no point to doing so. Is there, Joan?


  1. Santorum is just silly. One cannot and therefore should not and must not take votes to determine the accuracy of scientific descriptions of reality. That’s just silly. There is such a thing as reality, and it is possible to describe it. A valid test of the description’s accuracy is its correlation with other observations.
    Stalin of course insisted that scientists say what he wanted .”socialist science” to say. Santorum is copying him to make up “coal company science.” Both are just silly. Kids used tp be told a tale about an English king who commanded the waves to stop coming in. Too bad they don’t tell that story any more. If Santorum owned a condo on the beach, he would keep denying the rising waers as they washed through his condo’s windows.


  2. The Clean Power Plan is based on a false premise. Humans’ use of fossil fuels, and the resulting carbon dioxide air emissions, has no material effect on climate. Human activities cause only about 3% of all carbon dioxide (CO2) emissions to the atmosphere. Most of the rest are the result of decomposing plant material. CO2 is in equilibrium. It is a weak greenhouse gas in theory, but its actual climate effects are nullified by stronger forces, particularly the formation of mineral carbonates from atmospheric carbon dioxide.

    The theory of fossil fuels-caused climate change is a false premise for any regulation.
    1. CO2 does not materially affect the Earth’s climate; and,
    2. Nature already effectively captures and sequesters CO2 as mineral carbonate; and,
    3. Climate cycles are natural, and caused by forces other than CO2; and,
    4. The average residence time of CO2 in the atmosphere is 5 years; and,
    5. Human activities generate only about 3% of CO2 emissions. Most of the rest are from rotting plants.

    Anyone who passed 10th grade chemistry can conclude this using public information sources. Limestone and marble are the most familiar forms of mineral carbonate. CO2 is an essential component of mineral carbonate (CaCO3, for calcium). Carbonates are the ultimate repository of atmospheric CO2. Carbonates form in seawater and soils through biological and chemical processes. The formula is CO2 + CaO => CaCO3. Virtually all carbonates are formed from atmospheric CO2 that is taken up by seawater or soils. You can make magnesium carbonate in your kitchen by mixing carbonated water with milk of magnesia.

    The detailed perspective is presented in the paper http://www.co2web.info/ESEF3VO2.pdf by Danish researcher Tom Segalstadt. The paper is not “peer-reviewed”, but seems rigorous. (It has recently been shown that “peer review” really means “crony review”.) Activists use ad hominem arguments to dismiss the paper, as they do any argument they dislike.

    Fossil fuels (especially coal) producers and users are being persecuted in unprecedented fashion—a literal pogrom. A 21st century Scarlet Letter. It is now known that Soros-related investors and other progressive interests are buying up coal assets at deep discounts from their recent values. It seems like a Joe Kennedy “bear raid”. We should take a holistic view of this regulatory and political process. Where is it taking us? Who wins? Who pays? How is the public served?

    The media, regulatory and political structure built on the false premise of fossil fuels-caused climate change is a house of cards. Fossil fuels producers are uncompensated victims. The Federal government in the past compensated tobacco interests, and even some slave owners losses incurred in remedying proven harms. But fossil fuels caused global warming is unproven.

    If the Federal government really intended to change the methods of generating electric energy as part of a good-faith effort to produce a public good, the businesses that have sunk significant capital into these so-called “stranded assets” should have been compensated. Fifty billion dollars, more or less, would have done the job. Many affected businesses would have willingly cooperated.

    But that is not what the government intended. It now seems that it intended to drive down the value of those assets so politically connected cronies could “pick up the pieces” at deep discounts, after which fossil fuels will be, no doubt, rehabilitated under new ownership. This process was conducted in bad faith. “Secret science”, shadow communications, deceit and lies are commonplace at the involved Federal agencies. See “The Liberal War on Transparency” by Christopher C Horner; ISBN 978-1-4516-9488-8 and “The Deliberate Corruption of Climate Science” by Dr. Tim Ball; ISBN 978-0-9888777-4-0.

    Businesses adversely affected by this process may have claims at law. These could include commercial defamation, and interference with contracts and prospective advantages. If it can be shown that parties acted in concert to deceive the public and were unlawfully enriched or caused damages, conspiracy and racketeering charges are in play. Further, if government and NGO officials acted with gross negligence or willful misconduct (ie, lying, cheating and fabricating evidence) any indemnities from their respective employers would be null and void. They could be held personally liable.


    1. I’m a scientist. I figured it out for myself. The Segalstadt paper provides background.

      If you’re so smart, why don’t YOU tell us where limestone and other carbonate minerals come from?


    2. In an earlier comment, I said that it is dumb to take votes on matters of fact. Either a statement accurately describes a fact or it doesn’t. If a statement is erroneous, it doesn’t matter if thousands or even millions praise the statement. It’s still wrong.

      Here you go to the opposite extreme, citing one person. Have you evaluated his evidence?? Do you know anything about the subject? Enough advanced math to evaluate the authors scenarios? If not, then you have no way of knowing whether his statements are more accurate than the thousands of scientists who hold the opposite view.

      There is another point of logic to be made. The vote-takers say we should not act because we have uncertainty. The opposite is true. Great uncertainty means action must be taken NOW. It’s like Runsfeld’s “unknown unknowns.” In cases of uncertainty, one does not know all the possible consequences. Yes; it’s possible that man-made climate change won’t cause any harm. But, in the case of this uncertain subject, it’s also possible that the harm will be much greater than we think today.

      So you are saying we should take enormous risks–some known; some that will be unexpected–merely to save a few pennies.


  3. the evident consensus resulting from metadata studies (always subjective) could be as low as 0.3%. This matter has been completely aired out, and is irrelevant, so I won’t go into it any further here. If you want to know more, just search “97% consensus”


    1. Miner,

      I have no idea what you are saying. I am familiar with most of the studies about this issue (the major ones are discussed here), and they all find overwhelming agreement that the Earth is warming — with anthropogenic factors a major role since WWII. The PBL study shows that a small majority support the the AR4 and AR5 findings about greenhouse gases at the 90% level (it’s the only one to ask about specific confidence levels).

      I have seen nothing showing support among climate scientists for these propositions “as low as 0.3%”. Also, since the number of studies is so few (roughly a dozen), why use metadata studies? Also, ?metadata studies”? How many have there been?


    2. All of the studies regarding “consensus” are metadata studies. That is, the researcher reviews the work of others (but no original work of his own) and arbitrarily sorts the others’ work into categories. Not scientific.


  4. The true “consensus” is found in the Model results. 100% of the models fail the scientific method. According to both NOAA and the UK MET “Near-zero and even negative trends are common for intervals of a decade or less in the simulations, due to the model’s internal climate variability. The simulations rule out (at the 95% level) zero trends for intervals of 15 yr or more, suggesting that an observed absence of warming of this duration is needed to create a discrepancy with the expected present-day warming rate.”

    RANSLATION – A standstill of 15 years or more invalidates the models.It has been over 19 years.

    When examined, 100% of the IPCC Models have been invalidated.

    [img] https://informativestats.files.wordpress.com/2013/10/hayden_ipcc_arrow.jpg [/img]


    [quote]This beautiful graph was posted at Roy Spencer’s and WattsUp, and no skeptic should miss it. I’m not sure if everyone appreciates just how piquant, complete and utter the failure is here. There are no excuses left. This is as good as it gets for climate modelers in 2013. John Christy used the best and latest models, he used all the models available, he has graphed the period of the fastest warming and during the times humans have emitted the most CO2. This is also the best data we have. If ever any model was to show the smallest skill, this would be it. None do.[/quote]


    1. amirlach,

      “100% of the models fail the scientific method.”

      You don’t appear to be clear how the scientific method works. That the current generation of models didn’t predict the pause does not mean that they “fail the sci method”. Incomplete models are the essence of science.

      Most models fail at some point — as Newton’s does for objects at near-relativistic speeds. Such results show the model’s limitations, for future work to either improve (Kuhn’s “normal science”) or replace the model (Kuhn’s “paradigm revolution”).


  5. Consensus is BS. The Ptolemaic view of the universe was “consensus” for two millennia and it was wrong, Wrong, WRONG !!! No more need be said on consensus.


    1. derfel,

      For scientists the consensus is essential operationally, in terms of having a paradigm that focuses & coordinates their effort. It might eventually prove largely correct — or wrong. Either way it is useful.

      Determinging the consensus in a field at a specific point in time is a useful marker for historians of science. Like a milestone on a road, it has no special significance but is useful nonetheless.

      The essential utility of the consensus is for public policy. Decision makers rely on science. Since they’re not experts, they need to know not just what’s the consensus — but also the degree of consensus: what fraction of relevant experts agree, and what is their level of confidence in the consensus (they might all agree that X is perhaps true).


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