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Climate scientists' views on climate change: a survey

Hans von Storch and Dennis Bray

In 1996 and 2003 we surveyed the opinions on climate change held by climate scientists. The results of these surveys have been subject to many misuses and erroneous claims. Some have selected individual statements out of context (scroll down to number 5) to bolster their claims, while others have argued that the 2003 part of the survey would be strongly biased by skeptics misusing the online-sampling for multiple submissions.

With respect to the latter – the survey was conducted first in 1996 with a mail-out format, which nobody claimed could be biased and the results were published in the Bulletin of the American Meteorological Society. The second survey from 2003 was conducted on the internet, a procedure that in principle could have been misused by multiple submissions by those skeptical or alarmist on climate change who shared the password. However, the 2003 results are internally consistent with the 1996 results. In 2003 scientists expressed increased satisfaction and agreement with the IPCC and increased confidence in the tools of the science. In comparison to 1996, no anomalies were found in the response to questions.

On the skeptical side, the survey has often been used to create the impression that most scientists were not in support of anthropogenic causes of ongoing climate change: Specifically, it was noted that “For example more climate scientists ‘strongly disagree’ than ‘strongly agree’ that climate change is mostly the result of anthropogenic causes.” This interpretation is certainly biased.

We had requested responses on a scale from 1-7 to the question “Climate change is mostly the result of anthropogenic causes.” – with 1 representing “strong agreement” and 7 “strong disagreement”. Thus, scales 1-3 signal agreement, 4 an ambivalent position, and 5-7 disagreement. The frequency distribution for the two surveys in 1996 and 2003 are:
chart.JPG
Thus, the statement, that more respondents strongly disagree than strongly agree is technically correct (10% vs. 9%), but highly misleading. If we pool the 1-3 positive responses to “agreement”, and 5-7 to disagreement, then the ratio in 1996 was 41:45 in favor of disagreement; in 2003, however, this ratio has become 56:30 in favor of agreement; all scales 1-3 have seen strong increases in frequency, while 5-6, with the notable exception of scale 7, have seen marked reductions.

Furthermore the question refers to “climate change” in general. We intended to ask for responses to the statement "Ongoing climate change is mostly the result of anthropogenic causes", but some respondents may have considered Holocene climate change in general. Thus, “disagreement” with the statement does not necessarily signal doubt about the perspective of a dominantly man-made climate change in the coming decades, but it mostly reveals an assessment of presently emerging climate change. The problem is that some commentators interpret our numbers as responses to "Future climate change is mostly the result of anthropogenic causes". "

One should also consider the possibility that scientists, who are naturally “plagued” or honored by doubts, may have a hard time choosing maximum confidence (i.e., category 1); therefore many may prefer a weaker “2”. (This tendency is obvious when we ask for assessment of the skill of models, and the respondents are hesitant to go for maximum confidence).

After careful quality checks, which lead to the identification of a few errors related to incorrect coding of answers, the responses of the 2003 survey have now recently been published.

We are presently preparing a new survey; this time, we will implement a more efficient barrier for manipulating response rates, even if we do not believe that this was really an issue in our 2003 survey. As the purpose of the survey is intended to be of service to the scientific community, we would openly welcome questions posed by the community to be added to the upcoming survey. However, please keep in mind that the survey poses general rather than specific questions and that the length of the survey is a major consideration.

Hans von Storch and Dennis Bray
Institute for Coastal Research
GKSS Research Center
Max Planck Str. 1
21502 Geesthacht

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Dear Dennis and Hans,

I have a few queries on your survey.

Firstly, you say how the recipients were chosen in the report, but say that this was not random. Could this have biased the results? In the second article you link to, it suggests that the survey was posted to a climate skeptic mailing list. Can you verify whether that is true and whether that could have resulted in a bias in responses?

Secondly, I understand your point that people who said they didn't agree with the statement "climate change is mostly the result of anthropogenic causes" may believe that future warming will result from human activity, but perhaps don't believe that presently emerging climate change is attributable to human activity.

But if there is that large a caveat on interpreting the results, I'm personally at a bit of a loss to see how they are meaningful....unless there is further information on why respondents chose certain categories.

And lastly, you don't mention the survey published in Science by Oreskes in 2004 on climate scientists’ views of climate change (http://www.sciencemag.org/cgi/content/full/306/5702/1686), which reviewed 928 abstracts in scientific journals published between between 1993 and 2003. This showed that not a single paper disagreed with the consensus that Earth's climate is being affected by human activities. Why is that, seeing as it so highly cited and effectively the results of your survey challenge the findings?

Thanks, Olive

I am extremely disappointed that von Storch and Bray continue to maintain that their 2003 represents the views of climate scientists. The URL and password were posted to a sceptics' mailing list. This obviously biases the results and means that reponses from people who were not climate scientists were included.

The phrase "climate change is mostly the result of anthropogenic causes" is open to interpretation in a variety of other ways. How is "mostly" defined, e.g.? The only unconfusing way to ask such a question is to conform its terminology with that used in the AR4.

As well, I think it's generally understood in the survey business that polls of this sort are intrinisically unreliable.

I agree with Steve Bloom.

Seeing as you are planning another survey, my first suggestion would be that you make the questions much more specific , perhaps by conforming to the terminology used in the AR4.

Also do you have a suggestion of how you will ensure unbiased sampling in the next survey?

I think the question re Oreskes is interesting. Strictly speaking Oreskes survey was of papers, not scientists views, but how can it be that 10% of scientists apparently strongly disbelieve that climate change is mostly due to humans, but not one of them has published anything saying so?

Is there a block of people convinced of this, but not actually doing any research or publication?

Or was the question badly misinterpreted? As you note, its ambiguous - someone with an ice core or geological perspective, thinking of longer timescales, could perfectly well disagree.

What was the name of the skeptic mailing list? If it had an archive, it should be fairly easy to determine if the survey was FREEPED, or at least whether the possibility was discussed.

I have three additional questions for your next survey of climate scientists:

1) Do you think that predictions, forecasts, or projections of future climate must be falsifiable, in order to be scientifically valid?

2) Are the IPCC Fourth Assessment Report temperature projections in Table SPM-3 (Summary for Policymakers Table 3) falsifiable?

3) From reading AR4 Table SPM-3 and the rest of the Fourth Assessment Report, what is the IPCC saying is the most likely warming in 2090-2099, relative to 1980-1999):

a) less than 0 deg C (i.e., cooling),

b) 0-2 deg C,

c) 2-4 deg C,

d) 4-6 deg C,

e) greater than 6 deg C, or

f) don't know (the IPCC does not say what the most probable warming or cooling will be).

We appreciate the comments we have received, which certainly will help us to use the data of the present survey better, and to improve the next survey. Here are short answers to some of the issues raised on the blog.

a) Bias - first, we already addressed the problem in the 2nd para. 2nd - how big would you assume that bias be, given the consistency with the unbiased results from 1996? If all 7's were from skeptics, who many seem to consider not qualified to participate - what about the 4-6 group, which is not really supportive of the statement, but slightly or even a bit more skeptic. 20-30% have reservations to respond positive to our question.

b) Oreskes - her piece has not sufficiently and openly discussed in the public in spite of valid methodical questions (which in the course of the debate may turn out not to be a problem, after all – but a critical debate is a prerequisite to make conclusions robust and valid; such discussions are not an insult nor a digression) It is rather sad that “science” has avoided an open discussion, by rejecting a series of comments. Dennis Bray was among the commentators, and I believe his comment is available on the net for those interested (he is presently on vacations so that I can not provide a link).

c) We certainly should have worked harder to formulate more precise question. The problem was, and is, however, that we started this in 1996, and we were interested in continuity across years and comparability across surveys; since in 1996 the AR4 did not exist, we could not use that terminology - also it is not sure that everybody adopts this terminology. In any case, with the next survey we will have to work on the questions, by either reformulating them or adding short explanatory texts.

d) Somebody raised the question who would be a scientists, i.e. a person who would be allowed to register with the survey. The answer is certainly not “anybody with a natural science degree agreeing to the IPCC”; a possible answer would be “anybody with an academic degree in meteorology, oceanography, physics (chemistry, math, ecology…?), who has invested some time into the issues”. Would we consider Fred Singer a legitimate member of that group? What about Nick Stern? What about David King, the former “Chief Scientist to the British Government”?

Do you have any response to the piece by Jeff Jacoby in yesterday's Boston Globe that references your survey?

The link to the Boston Globe article is here:http://www.boston.com/news/globe/editorial_opinion/oped/articles/2007/08/19/warming_debate_scene_1_take_2/

Yes, I have a response to Jeff Jacoby in the Boston Globe (http://www.boston.com/news/globe/editorial_opinion/oped/articles/2007/08/19/warming_debate_scene_1_take_2/). He quotes, and he quotes are mostly technically correctly. He did not bother to talk to us.

The journalist has looked at our material and has drawn other conclusion from the material than I would have done. That is his good right. Only ideologists and naïve people believe that the authority of interpreting data is only with the person who publishes the data. Of course, we scientists should oppose when the data are technically misquoted or misunderstood; if, however, different conclusions are drawn, so be it.

We need a debate about the role of science and of media. Media are not “secretaries” of scientists, who have to report not only the data faithfully but also have to share in their writing intentions and broader assessments; instead it is a key role of media to present their own critical and holistic perception of processes and phenomena, in particular when social processes are involved – with science being one of these social processes.

Science, on the other hand, should come to grabs with the fact that science is taking place in a social context, so that our practice is influenced by values and culturally constructed views – the way we ask, the criteria we apply before accepting explanations. History of science – see the “Genesis and Development of a Scientific Fact” by Ludvig Fleck – informs us that we hardly get the full picture; that science has to “adjust” its knowledge claims, when new empirical evidence arrives; sometimes, we even have to come up with a new paradigm.

When Jacoby would have asked me, then I would have advised him not to write “Plainly, the science isn't settled. It changes all the time.” Which “science”? Instead, I would have preferred to read “Plainly, there are many scientific questions open; we need many refinements and some revisions of knowledge, but the basic concept is really broadly accepted in the scientific community - that man is changing climate in a detectable way, and that this change will grow to levels causing significant impacts beyond the range of natural variability; that we may limit these changes by reducing the emission of greenhouse gases”. Mr. Jacoby preferred to formulate his conclusions differently.

Obviously, Mr Jacoby had his opinion on the issue to begin with, and just picked from our survey what he thought fits best for his case – as people with vested interests do. This is a common practice, and the purpose of our original comment was to point out that our results are used in this way.

We have to live with the Mr.’s Jacoby of the world, on both side of the debate. It should be no excuse for us to patronize an open and democratic society by prefiltering scientific results to avoid misuse by parties and views we personally do not support.

The answer is certainly not “anybody with a natural science degree agreeing to the IPCC”

I think an interesting question to confront this problem might go something like:

How comfortable do you feel answering any of these questions with certainty?

I think the focus on the 1-3 vs 5-7 responses are the real story, as the authors point out. The migration from scepticism to agreement really does stick out for me.

With respect to responses at the 1 & 7 extremes: would it be valid to exclude those as "outliers", and then just talk about 2-3 vs 5-6? My reasoning is that this would avoid letting the most vocal proponents of both sides drown out the rest of the scientists.

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