Responses to the Climate Science Survey


Appeared in similar form on the PBL website

In the Spring of 2012, the Netherlands Environmental Assessment Agency PBL held a survey among 1868 scientists studying various aspects of climate change, including physical climate, climate impacts, and mitigation. The main results of the survey were published in an article in Environmental Science and Technology (ES&T) in August 2014: “Scientists’ views about attribution of global warming”. It showed that there is widespread agreement regarding a dominant influence of anthropogenic greenhouse gases on recent global warming. This agreement is stronger among respondents with more peer-reviewed publications.

A background report with the results for all 31 questions has now been made available. The total number of responses for each answer option is provided and a subdivision into seven groups for five questions. The background report contains previously unpublished data. Some highlights are provided below.

Climate sensitivity

Respondents were asked for their opinion regarding the best estimate and likely range for equilibrium climate sensitivity (ECS). This is an important quantity for projections of global warming, as it gives the expected warming that would follow from a doubling in atmospheric CO2 concentration after the climate system has equilibrated to the new conditions. Thus, expected warming in the future depends on the combination of total emissions and climate sensitivity.

The figure below gives the average estimates of ECS from 7 groups of respondents, including authors of the Working Group I report of the fourth IPCC Assesment Report (AR4), respondents who signed public declarations critical of mainstream climate science as embodied by IPCC (‘unconvinced’), and four different subgroups distinguished according to their self-declared number of climate related peer-reviewed publications (0–3; 4–10; 11–30; more than 30). Results from most groups were very close to the IPCC range (1.5-4.5 °C) mentioned in the fifth assessment report (AR5) – except those tagged as ‘unconvinced’ which strongly deviated from the other groups, and to a lesser extent the group of respondents with three or less publications. For all subgroups the ‘best estimate’ was slightly lower than the ‘best estimate’ reported in AR4 (i.e. 3 °C). AR5 provided no best estimate.

Scientists views on climate sensitivity - PBL

Role of climate science in society

Respondents were also asked their opinion about seven statements regarding the role of climate science in society and how the science should be communicated. There was a strong consensus that scientists themselves should communicate with both policymakers and the general public about climate change and that communication with the general public should focus on solid knowledge. To a lesser extent there was agreement that risks and uncertainties should be emphasised during such communication. Responses varied more strongly about whether or not existing uncertainties in climate science strengthen the case for mitigation (i.e. to avoid potential low probability, high impact events). There was (strong) disagreement with the statement that climate science would be too uncertain to be useful for policymaking on climate change.

Scientists views on role of science in society - PBL

The role of the sun in global warming

In the public debate about climate change the role of the sun is often put forward as an alternative explanation for global warming. Question 17 asked what fraction of recent global warming could be attributed to the sun. Those tagged as ‘unconvinced’ had the lowest fraction of respondents that indicated that they don’t know (together with AR4 authors) and the highest fraction that said that the role of the sun is unknown. As expected they also had by far the highest fraction (27%) that believed that the sun caused more than half of recent global warming.

As with the attribution questions (see the ES&T article), there appears to be a trend in responses going from the group with fewest publications to those with most. The more publications about climate change respondents report to have written, the larger fraction of them agree with the IPCC position that the sun hardly played a role in recent global warming, since the solar output decreased slightly over that period.

Scientists views on the role of the sun in global warming - PBL

More information:

PS: I’ll have a poster presentation about the survey at the EGU conference this week, in session EOS6 “Communication and Education in Geoscience” on Thursday evening.


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8 Responses to “Responses to the Climate Science Survey”

  1. thomaswfuller2 Says:

    Looks like lots of candidates for the League of 2.5.

    Thanks for this, Bart. Did you run this through SPSS or is it in Excel?

    And of course, the same old question–is the data available for examination?

  2. thomaswfuller2 Says:

    I am starting to review the results of the survey. You might be interested in my initial comments here:

  3. Editor of the Fabius Maximus website Says:

    Follow-up on this fascinating and important information. Have you posted any more about it?

    For example, you show the one standard deviation range for estimates of ECS. For public policy uses the 2 SD range would be more useful to know.

  4. Bart Verheggen Says:

    Fab Max,
    We asked respondents for their best estimate and likely (one stdev) range (corresponding to how the IPCC reports its main conclusions about ECS); not for the two stdev range, so no.

  5. Editor of the Fabius Maximus website Says:

    Thank you for the follow-up reply. There have been many surveys of climate scientists on these matters. IMO yours was the best yet in both construction and depth..

    I wrote about it here:

    Judith Curry posted a comment at her website saying she was going to do a post about this.

  6. thomaswfuller2 Says:

    I take issue with both of you here:

    Bart, I am highly critical of the paper written by you, John Cook, et al:

    In all of his writing on the results of the survey, Bart Verheggen has focused exclusively on the higher agreement with the IPCC shown by scientists with more publications.

    Indeed, in a paper written with John Cook, among others, Verheggen does not even report the top line statistic of his finding–that 66% of the scientists he surveyed agree that half or more of recent warming is caused by human emissions of greenhouse gases.

    This is astonishing. That a report on a survey would not show and discuss the headline finding is bizarre. It would be like writing a report based on what Donald Trump’s supporters think of Mexican immigrants without even reporting what the overall population thinks.

    It is legitimate to focus your analysis on the numbers of interest to you–even if that interest is only sparked by the fact that the entire numbers don’t support your position. But it is not at all legitimate practice to fail to report the top line data.

    Verheggen’s failure to report the real numbers of his survey in my mind invalidates the rest of his paper. I know Bart Verheggiightly through extended conversations at his blog and via emails. He has always been fair and honest with me. I find this incident bizarre, but the participation of John Cook in this paper may well explain it. John Cook is the author of a paper that should by now be completely discredited that reports the consensus at 97%. It is junk science and should be treated as such.

    As for the position adopted by Verheggen’s report, it may well be that scientists with more publications are a better judge of attribution than scientists with fewer articles to their credit.

    But we don’t know that. Verheggen et al make no attempt to show why that would be the case and they don’t even really make the argument. There is nothing in the survey that would show greater expertise on their part and there are a number of reasons to question that assumption, for assumption is all it is.

    Scientists working in the private sector may have equal or even superior expertise than academics who must publish or perish. New scientists may be even more conversant with new information and data than older scientists who may not feel they have to keep up with the latest data. Scientists who get their name added to 10 multi-author publications may have no more expertise to offer than their colleague at the next desk who writes only one paper.

    In any event, Verheggen et al don’t even try to make the case. They simply ignore the 66% consensus shown by all the respondents to his survey and report only on the differences in opinion shown by those with differing numbers of publications.

    So at the end of the day, what a surprise. Advocates for skeptics and alarmists look at the same data and come up with different answers. Neither advocate tells an untruth. Both strain at gnats and swallow camels to come up with an answer that they like. Both the answers that they like are gross distortions of reality.

    The consensus is real, although it looks more like a majority. It is not the nonsensical 97% shown by John Cook. It is not the 47% shown by Fabius Maximus. Verheggen doesn’t even show it at all.

  7. Bart Verheggen Says:


    We reported all the numbers, including your favored 66%, both in the main text (p4 of EST paper) and in table S3 in the Supporting Information. So your allegation is incorrect. I’ve told you this before.

    You on the other hand quote only one number, based on only one of the two relevant questions, with the lowest result. A number which would be very different if you’d deduce a similar ratio from the other question. Why would they be so different? Because Q1 was more difficult to answer to the level of precision required by the answer options.

    A more detailed answer to both you and Fab Max is forthcoming.

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