New survey of climate scientists by Bray and von Storch confirms broad consensus on human causation

Bray and von Storch just published the results of their latest survey of climate scientists. It contains lots of interesting and very detailed information, though some questions are a little biased in my opinion. Still, they find a strong consensus on human causation of climate change: 87.4% of respondents are to some extent convinced that most of recent or near future climate change is, or will be, the result of anthropogenic causes (question v007). Responses were given on a scale from 1 (not at all) to 7 (very much). In line with Bray (2010) a response between 5 and 7 is considered agreement with anthropogenic causation. In their 2008 survey the level of agreement based on the same question was 83.5% and in 2013 it was 80.9%.

How convinced are you that most of recent or near future climate change is, or will be, the result of anthropogenic causes? (v007)

not at all   1     2     3     4     5     6     7   very much

Question v013 asked a somewhat similar question as we did in our 2012 climate survey, namely the percentage of global warming that is attributable to human activities:

Since 1850, it is estimated that the world has warmed by 0.5 – 0.7 degrees C. Approximately what percent would you attribute to human causes? (v013)

1=0%   2=1-25%   3=25-50%   4=51-75%   5=76-100%

84.2% of respondents picked one of the two answer options that correspond to the canonical “more than half” or “most” of global warming that according to the IPCC is human caused. However, the corresponding IPCC statement is with regards to warming since the 1950’s, about which there is a lot more confidence, whereas this question specifies the warming since 1850.

But wait a moment, hasn’t the earth warmed a lot more than 0.5-0.7 degrees C since 1850? Yes, it definitely has; we’ve recently breached the 1 degree mark relative to the 1850-1880 average, so the range given in their question is quite outdated. A defensible choice at the time of drafting the survey would have been to quote the latest IPCC number of 0.85 (0.65 to 1.06) degrees warming over the time period 1880-2012, even if current temperatures have gone up sharply since then.

Global average surface temperature relative to the 1850-1880 mean. Last annual average shown is 2015; if the first few months of 2016 are a guide, the vertical scale might have to be adapted for 2016. Figure by Jos Hagelaars.

Moreover, the answer options for v013 do not cover the full range of possibilities. Natural factors could have caused warming or cooling. Imagine that natural factors would have caused a cooling of 0.1 degrees C since pre-industrial times (which is not at all implausible), then to achieve closure with the observed warming of 1.0 degrees, anthropogenic factors should have contributed 1.1 degrees, or 110% of the observed warming. We discussed this argument in detail in our ES&T paper emanating from the climate science survey we conducted in 2012.

I emailed Dennis Bray about these and other issues after having responded to their survey back in 2015. He defended their choice of lowballing the observed warming as being consistent with their previous surveys and not being much different from more recent, and also likely contested, estimates. Strangely, he disagreed with the possibility of a factor being responsible for more than 100% of the observed warming, even in the hypothetical example above.

Cook et al (myself included) recently wrote an article in which we reviewed the existing ‘consensus’ estimates. This latest Bray and von Storch survey finds a level consensus on attribution that is consistent with other studies, though towards the lower end of the range. From their description I don’t think there is a bias in their sample of scientists, though there is always the possibility of self-selection, where people might be more likely to respond to a survey if it originates from a source who they perceive to be credible. Repeatedly, surveys have found that the level of consensus goes up as you zoom in to a sample of scientists with more relevant expertise. The Bray and von Storch results, as are ours, are mostly representative of a broad group of climate related scientists.

A detail of particular interest to me is that the survey questions included the response option “no answer”. That explains the different sample size for different questions (“Number of obs”). It’s probably no coincidence that question v013 (asking for a specific range of percent contribution) has a smaller sample size (n=587), and by inference more “no answer” responses, than the other, but simpler, attribution question v007 (n=640). This is consistent with what we found in our 2012 climate science survey: fewer respondents picked a specific percentage range of attribution compared to providing a qualitative judgment thereof. Though admittedly “no answer” (in the Bray and von Storch survey) is less ambiguous in this context than “I don’t know”, “unknown” or “other” (in our survey).

Amidst the questions on science and society I perceived some questions to have an “anti-consensus” (v069) or “anti-alarmist” (v067) tone to it, but there were no questions asking for mirror image perceptions. Doomsday stories need to be investigated before they get out of hand (v067): of course. But no question was asked whether stories downplaying a scientifically established risk should be investigated. I would have likewise responded: of course. To his credit, Dennis Bray acknowledged in his email that this was an oversight on their part.

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Rick Santorum misrepresents our climate survey results on Bill Maher show

In our survey of more than 1800 scientists we found that the large majority agree that recent climate change is predominantly human induced. The article where we discuss our results is publicly available and a brief rundown of the main conclusions is provided in this blogpost.

We were quite surprised to hear a US Presidential candidate, Rick Santorum, make the opposite claim based on our survey. On the Bill Maher show he said:

The most recent survey of climate scientists said about 57 percent don’t agree with the idea that 95 percent 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. There’s hundreds of reasons the climate’s changed.

What did we actually find in our survey?

In our survey of 1868 scientists studying various aspects of climate change, we asked two questions about the causes of recent global warming. Of all scientists who provided an estimate ~85% think that the influence of human greenhouse gases is dominant, i.e. responsible for more than half of the observed warming. ~15% think greenhouse gases are responsible for less than half of the observed warming. If you zoom in to those respondents with arguably more expertise, the percentage agreeing with human dominated warming becomes 90% or larger.

The existence of a strong scientific consensus about climate change is also clear from previous surveys of scientists and of the scientific literature and from statements of scientific societies. A scientific consensus is a logical consequence of the evidence for a certain position becoming stronger over time.

Rick Santorum’s claim is misleading and wrong because:

1) it is based on a wrong interpretation of just one of the two survey questions about the causes of recent climate change.

2) it is based on the argument that respondents who didn’t provide a specific estimate for the contribution of greenhouse gases (22% of the total number) think that this contribution is small. That is a wrong inference.

3) it is based on the argument that respondents who think it is “very likely” or “likely” or “more likely than not” that greenhouse gases are the dominant cause of recent warming disagree with this dominant influence. That is a wrong inference.

Politifact also did a fact-check of Santorum’s claim and found it to be false. It gives a very good overview of what’s wrong with Santorum’s claim. Several people are quoted in their article, myself included as well as the blogger Fabius Maximus who came up with the 43% consensus figure used by Santorum to claim a 57% dissensus:

PBL survey shows strong scientific consensus that global warming is largely driven by greenhouse gases

Updates:

(5 Sep 2015): US Presidential candidate Rick Santorum used an erroneous interpretation of our survey results on the Bill Maher show. My  detailed response to Santorum’s claim is in a newer blogpost. Politifact and Factcheck also chimed in and found Santorum’s claims to be false. The blogpost below goes into detail about how different interpretations could lead to different conclusions and how some interpretations are better supported than others.

As Michael Tobis rightly points out, the level of scientific consensus that you find “depends crucially on who you include as a scientist, what question you are asking, and how you go about asking it”. And on how you interpret the data. We argued that our survey results show a strong scientific consensus that global warming is predominantly caused by anthropogenic greenhouse gases. Others beg to differ. Recent differences of opinion are rooted in different interpretations of the data. Our interpretation is based on how we went about asking certain questions and what the responses indicate.

To quantify the level of agreement with a certain position, it makes most sense to look at the number of people as a fraction of those who answered the question. We asked respondents two questions about attribution of global warming (Q1 asking for a quantitative estimate and Q3 asking for a qualitative estimate; the complete set of survey questions is available here). However, as we wrote in the ES&T paper:

Undetermined responses (unknown, I do not know, other) were much more prevalent for Q1 (22%) than for Q3 (4%); presumably because the quantitative question (Q1) was considered more difficult to answer. This explanation was confirmed by the open comments under Q1 given by those with an undetermined answer: 100 out of 129 comments (78%) mentioned that this was a difficult question.

There are two ways of expressing the level of consensus, based on these data: as a fraction of the total number of respondents (including undetermined responses), or as a fraction of the number of respondents who gave a quantitative or qualitative judgment (excluding undetermined answers). The former estimate cannot exceed 78% based on Q1, since 22% of respondents gave an undetermined answer. A ratio expressed this way gives the appearance of a lower level of agreement. However, this is a consequence of the question being difficult to answer, due to the level of precision in the answer options, rather than it being a sign of less agreement.

Moreover, the results in terms of level of agreement based on Q1 and Q3 are mutually consistent with each other if the undetermined responses are omitted in calculating the ratio; they differ markedly when undetermined responses are included. In the supporting information we provided a table (reproduced below) with results for the level of agreement calculated either as a fraction of the total (i.e., including the undetermined answers) or as a fraction of those who expressed an opinion (i.e., excluding the undetermined answers), specified for different subgroups.

For the reasons outlined above we consider the results excluding the undetermined responses the most meaningful estimate of the actual level of agreement among our respondents. Indeed, in our abstract we wrote:

90% of respondents with more than 10 climate-related peer-reviewed publications (about half of all respondents), explicitly agreed with anthropogenic greenhouse gases (GHGs) being the dominant driver of recent global warming.

This is the average of the two subgroups with the highest number of self-reported publications for both Q1 and Q3. In our paper we discussed both ways of quantifying the level of consensus, including the 66% number as advocated by Tom Fuller (despite his claims that we didn’t).

Fabius Maximus goes further down still, claiming that the level of agreement with IPCC AR5 based on our survey results is only 43-47%. This result is based on the number of respondents who answered Q1b, asking for the confidence level associated with warming being predominantly greenhouse gas-driven, as a fraction of the total number of respondents who filled out Q1a (whether with a quantitative or an undetermined answer). As Tom Curtis notes, Fab Max erroneously compared our statement to the “extremely likely” statement in AR5, whereas in terms of greenhouse gases AR5 in Chapter 10 considered it “very likely” that they are responsible for more than half the warming. Moreover, our survey was undertaken in 2012, long before AR5 was available, so if respondents had IPCC in mind as a reference, it would have been AR4. If anything, the survey respondents were by and large more confident than IPCC that warming had been predominantly greenhouse gas driven, with over half assigning a higher likelihood than IPCC did in both AR4 and AR5.

Let me expand on the point of including or excluding the undetermined answers with a thought experiment. Imagine that we had asked whether respondents agreed with the AR4 statement on attribution, yes or no. I am confident that the resulting fraction of yes-responses would (far) exceed 66%. We chose instead to ask a more detailed question, and add other answer options for those who felt unwilling or unable to provide a quantitative answer. On the other hand, imagine if we had respondents choose whether the greenhouse gas contribution was -200, -199, …-2, -1, 0, 1, 2, … 99, 100, 101, …200% of the observed warming. The question would have been very difficult to answer to that level of precision. Perhaps only a handful would have ventured a guess and the vast majority would have picked one of the undetermined answer options (“I don’t know”, “unknown”, “other”). Should we in that case have concluded that the level of consensus is only a meagre few percentage points? I think not, since the result would be a direct consequence of the answer options being perceived as too difficult to meaningfully choose from.

Calculating the level of agreement in the way we suggest, i.e. excluding undetermined responses, provides a more robust measure as it’s relatively independent of the perceived difficulty of having to choose between specific answer options. And, as is omitted by the various critics, it is consistent with the responses to the qualitative attribution question, which also provides a clear indication of a strong consensus. If you were to insist on including undetermined responses in calculating the level of agreement, then it’s best to only use results from Q3. Tom Fuller’s 66% becomes 83% in that case (the level of consensus for all respondents), showing the lack of robustness in this approach when applied to Q1.

Some other issues that came up in recent discussions:

• We cast a very wide net of respondents, including scientists who study various parts of climate change including impacts and mitigation.
• We made special efforts to include people with skeptical points of view, not all of whom are publishing climate scientists. As such, we probably slightly underestimated the strength of the scientific consensus.
• Our results are in good agreement with other opinion surveys, including e.g. Doran and Kendall-Zimmermann. Literature surveys such as by Cook et al generally find higher levels of consensus, since -as we also found, see figure just above- more published scientists are generally more convinced of human causation of global warming.
• See my comment at CCNF for a short discussion on the relevance of scientific consensus and pros/cons of evaluating it be means of literature survey or opinion survey.
• The background report with all survey questions and aggregated responses is basically an accompaniment to the article in ES&T and is based on the same data.

See also the basic summary of our survey findings and the accompanying FAQ.

 

Video-interview about climate science survey paper

Fellow Dutchman Collin Maessen interviewed me via skype about our recent paper “Scientists’ views about attribution of global warming“:

Collin wrote a blogpost about it as well which is well worth a read, giving a bit of context from other opinion and literature surveys.

The interview starts off with the general findings regarding the level of consensus, then focusing on how this compares with previous studies, how the media coverage is slanted towards contrarian views, and he gives me a chance to talk about my favorite part, how aerosol cooling masks the greenhouse warming and how this makes the phrasing of the IPCC AR4 attribution statement, by focusing only on the greenhouse warming part, prone to being misinterpreted. These aspects were also discussed in my blogpost from last month.

FAQ for the article “Scientists’ Views about Attribution of Global Warming”

published in Environmental Science and Technology (open access), DOI: 10.1021/es501998e, Supporting Information here.

A formal version of the FAQ is also available at the website of the PBL Netherlands Environmental Assessment Agency. A blog post with a brief description of the main conclusions is here.

 

General

1. What are the objectives of this survey?

The PBL aimed to characterize the spectrum of scientific opinion about physical climate science issues. The research was focused on issues that are a frequent topic of public debate, and explored questions such as:

• On which issues is there widespread agreement amongst scientists?
• On which issues do scientists hold varied opinions?
• How does the spectrum of scientific opinion compare to IPCC assessments?
• How do scientists view skeptical arguments and viewpoints?

2. What is the relevance of an opinion survey or of measurement of consensus in trying to assess the science?

Science is based on the critical evaluation of available evidence in the context of existing knowledge. It is not “just an opinion.” With this survey, we tried to identify how scientists assess the different viewpoints that exist in public discussions of climate science. If the evidence for a certain viewpoint has become sufficiently strong and stable over time, the scientists’ aggregated opinion could be expected to reflect that.

3. Are the survey results publicly available?

The full survey results are not publicly available, because the PBL intends to use the data for further analyses.
Update:
Graphs with the ‘straight counts’ for every question (i.e. the number of responses for each answer option) are available in a background report. These results are not segregated in different sub-groups.

 

Conclusions

4. How does this study compare to the often-quoted 97% consensus?

Our results are consistent with similar studies, which all find high levels of consensus among scientists, especially among scientists who publish more often in the peer-reviewed climate literature.

Cook et al. (2013) found that 97% of papers that characterized the cause of recent warming indicated that it is due to human activities. (John Cook, the lead author of that analysis, is co-author on this current article.) Similarly, a randomized literature review found zero papers that called human-induced climate change into question (Oreskes, 2004).

Other studies surveyed scientists themselves. For instance, Doran and Kendall-Zimmermann (2009) found lower levels of consensus for a wider group of earth scientists (82% consensus) as compared to actively publishing climatologists (97% consensus) on the question of whether or not human activity is a “significant contributor” to climate change. Our results are also in line with those of e.g. Bray and von Storch (2008) and Lichter (2007).

In our study, among respondents with more than 10 peer-reviewed publications (half of total respondents), 90% agree that greenhouse gases are the largest – or tied for largest – contributor to recent warming. The level of agreement is ~85% for all respondents.

While these findings are consistent with other surveys, several factors could explain the slight differences we found:

• Surveys like ours focus on opinions of individual scientists, whereas in a literature analyses the statements in individual abstracts are tallied. Literature analyses have generally found higher levels of consensus than opinion surveys, since the consensus is stronger amongst more heavily published scientists.
• This study sets a more specific and arguably higher standard for what constitutes the consensus position than other studies. For instance, Doran and Kendall-Zimmermann (2009) asked about human activity being a “significant contributor” to global warming, and Anderegg et al. (2010) investigated signatories of public statements, while we asked specifically about the degree to which greenhouse gases are contributing to climate change in comparison with other potential factors.
• Contrarian viewpoints are somewhat overrepresented in our survey and they may have overestimated their self-declared level of expertise (see question 9).

5. How is the consensus or agreement position defined?

The consensus position was defined in two ways:

• Greenhouse gases contributed more than 50% to global warming since the mid-20^th (Question 1). This is analogous to what was written in IPCC AR4.
• Greenhouse gases have caused strong or moderate warming since pre-industrial times (Question 3). “Moderate” warming was only interpreted as the consensus position if no other factor was deemed to have caused “strong” warming. This response means that greenhouse gases were considered the strongest –or tied for strongest- contributor to global warming.

The former definition exactly mirrors the main attribution statement in IPCC AR4 and served as a ‘calibration’ for the latter.

6. What does “relative response” mean on the y-axis of many Figures?

This gives the percentage of the respondents (often within a certain sub-group) for the specific answer option. We opted to show the relative response rather than the absolute response to enable comparing the responses of different sub-groups (with differing group sizes as denoted by N=…) within one graph.

7. What are “undetermined” answers?

Those are the sum of responses “I don’t know”, “unknown” and “other”.

8. Why do IPCC AR4 authors show a higher consensus than the other respondents?

AR4 authors are generally domain experts, whereas the survey respondents at large comprise a very broad group of scholars, including for example scientists studying climate impacts or mitigation. Hence we consider this to be an extension of the observation -in this study and in e.g. Anderegg et al. (2010) and Doran and Kendall-Zimmermann (2009) – that the more expert scientists report stronger agreement with the IPCC position. Moreover, on the question of how likely the greenhouse contribution exceeded 50%, many respondents provided a stronger statement than was made in AR4. Using a smaller sample of scientists, Bray (2010) found no difference in level of consensus between IPCC authors and non-authors.

9. How reliable are the responses regarding the respondent’s area of expertise and number of peer-reviewed publications?

Respondents were tagged with expertise fields, though these were in many cases limited and not meant to be exhaustive. These tags were mainly used to ensure that the group of respondents was representative of the group that the survey was sent to. A subset of respondents was also tagged with a Google Scholar metric. Those who were tagged as “unconvinced” reported more expertise fields than the total group of respondents and also a higher number of publications compared to their Google Scholar metrics, if available (see Supplemental Information).

10. Since most scientists agree with the mainstream and therefore most media coverage is mainstream, what is the problem with “false balance”?

Scientists with dissenting opinions report receiving more media attention than those with mainstream opinions. This results in a skewed picture of the spectrum of scientific opinion. Whether that is problematic is in the eye of the beholder, but it may partly explain why public understanding lags behind scientific discourse (e.g. the “consensus gap”).

 

Survey Respondents

11. How many responses did you get to the survey?

Out of 6550 people contacted, 1868 filled out the survey (either in part or in full).

12. How did you compile the list of people to be surveyed?

Respondents were selected based on

• keyword search in peer-reviewed publications (“global climate change” and “global warming”)
• recent climate literature (various sources)
• highly cited climate scientists (as listed by Jim Prall)
• public criticisms of mainstream climate science (as listed by Jim Prall)

13. Are all of the survey invitees climate scientists?

The vast majority of invitees are scientists who published peer-reviewed articles about some aspect of climate change (this could be climate science, climate impacts, mitigation, etc.). Not all of them necessarily see themselves as climate scientists.

14. Why did you invite non-scientist skeptics to take part in the survey?

They were included in the survey to ensure that the main criticisms of climate science would be included. They constitute less then 5% of the survey respondents. Viewpoints that run counter to the prevailing consensus are therefore somewhat magnified in our results.

15. How representative are the survey responses of the “scientific opinion”?

It’s difficult to ascertain the extent to which our sample is representative, especially because the target group is heterogeneous and hard to define. We have chosen to survey the wider scientific field that works on climate change issues. Due to the criteria we used and the number of people invited we are confident that our results are indeed representative of this wider scientific field studying various aspects of global warming. We checked that those who responded to the survey were representative of the larger group of invitees by using various pieces of meta-information.

16. Did you take into account varying levels of expertise of respondents?

Respondent were asked to list their area(s) of expertise and their number of peer-reviewed publications. These and other attributes were used to interpret differences in responses.

17. How did you prevent respondents from manipulating the survey results, e.g. by answering multiple times?

An automatically generated, user specific token ensured that respondents could only respond once.

18. How did you ensure respondent anonymity?

Survey responses were analyzed by reference to a random identification number.

 

Survey Questions

19. Are the survey questions public?

Yes, survey questions and answer options are available on the PBL website and as Supporting Information (part 2) to the article.

20. How did you decide on the questions to ask?

The survey questions are related to physical science issues which are a frequent topic of public debate about climate change.

21. Was the survey reviewed before it was sent to respondents?

Yes, before executing the survey it has been extensively tested and commented on by various climate scientists, social scientists and science communicators with varying opinions, to ensure that questions were both clear and unbiased. Respondents were not steered to certain answers.

——-

Reference: Bart Verheggen, Bart Strengers, John Cook, Rob van Dorland, Kees Vringer, Jeroen Peters, Hans Visser, and Leo Meyer, Scientists’ Views about Attribution of Global Warming, Environmental Science and Technology, 2014. DOI: 10.1021/es501998e. Supporting Information available here.

Please keep discussions on this thread limited to what is mentioned in this FAQ and to other questions you may have about the survey or the article. Discussion of the survey results should be directed at the more generic blog post.

The role of scientific consensus in moving the public debate forward

Mike Hulme had an interesting essay at The Conversation, the main message of which was

In the end, the only question that matters [for the public debate about climate change] is, what are we going to do about it?

Hulme correctly argues that the basic science is clear enough so that for society the important issues to discuss are not science related, but policy related. I argued much the same here. He writes:

What matters is not whether the climate is changing (it is); nor whether human actions are to blame (they are, at the very least partly and, quite likely, largely); nor whether future climate change brings additional risks to human or non-human interests (it does).

Let’s leave the minor quibble aside that AR5 puts the anthropogenic contribution at ‘extremely likely’ having caused more than half of the recent global warming.

The part where I disagree with Hulme is where he argues that showing the existence of a scientific consensus on the above (it is warming; it’s due to us; it’s bad news) somehow stands in the way of  getting society to discuss that most important question. I think the opposite is true. It is the continuous doubt about the science, sowed by those who oppose a serious discussion about what to do, that is a stumbleblock. Showing that a consensus amongst experts exists would enable society to more swiftly move on to the important conversation on what to do about it. I agree with Hulme that on this deeply ethical question there is, and ought to be, a multitude of opinions.

As Stephan Lewandowsky and John Cook write in a response to Mike Hulme:

The public’s perception of that scientific consensus is necessary to stimulate political debate about solutions.

Another element that’s missing from this discussion is that scientific and ideological arguments  should be clearly distinguished from each other (“is” vs “ought”).

Unfortunately, ideological arguments are often dressed in a sciency-looking cloak. From that perspective, I appreciate the honesty in Lindzen stating blunty “we’ll all be dead by then”, the obvious implication being: so why care. That’s indeed what a lot comes down to: How do you value the future compared the present?

IPCC history and mandate

The purpose of the IPCC was to assess the state of knowledge on the various aspects of climate change including science, environmental and socio-economic impacts and response strategies.

I.e. it was meant to report on and asses the scientific knowledge. This includes the question of how much evidence and (as a result) how much agreement amongst experts (consensus) there is for human induced climate change.

Some science historians point to other important aspects of IPCC’s history. The National Academy of Sciences wrote in 1979:

A plethora of studies from diverse sources indicates a consensus that climate changes will result from man’s combustion of fossil fuels and changes in land use.

Oreskes shows that the IPCC was set up in response to the emerging consensus in the 70’s/80’s that global warming due to GHG emissions would likely become a problem.

Spencer Weart writes:

The concern [about impending climate change] gave rise to the IPCC.

And also points to the Reagan administration being in favor of the clumsy IPCC approach, hoping that it would downplay the scientists’ fears.

When pointing to scientists who disagree with the IPCC consensus, it is important to note that people can agree in basically two directions. The survey by Brown, Pielke Sr and Annan for example shows this to be an approximate bell curve: Most (45-50%) of the respondents (scientists) more or less agree with the main thrust, and sizeable minorities (15-20%) think that IPCC overstated or understated its case. I discussed this survey and the broader question of why the consensus matters before. And I probably will pick this up again soon.

Scientifically, the more uncertain areas are the most interesting. However, if I look at the political decision making in terms of emission reductions and knowledge of the big picture (and the length of time that we’ve known about this big picture, albeit in gradually more certain terms), I can’t but conclude that the politics is hopelessly lagging behind the scientific knowledge in taking this problem seriously. (see e.g. my Dutch post “tijd voor de politiek om wetenschap serieuzer te nemen”.) Of course I’m aware that there’s more that informs politics than just the science, but still, there seems to be an uncomfortably big disconnect there. Stark warnings from science are ignored at our peril.

At this point in time, the uncertainties are pretty much irrelevant for policymaking, because any realistic change in the uncertain details is not going to affect the main trust of what we know, and thus the policy response that people may favour. For the long term, of course we need to finetune our knowledge, so research is still needed. (Hey, I’m a scientist, so I kind of have to say that, right?)

As Herman Daly said:

“Focusing on them [the big picture of what we know] creates a world of relative certainty, at least as to the thrust and direction of policy.” On the other hand, focusing on the more uncertain rates and valuations creates “a world of such enormous uncertainty and complexity as to paralyze policy”.

Perhaps that’s indeed what’s happening now, also cf. Judith’s uncertainty monster and complexity monster.

“To make the point more simply, if you jump out of an airplane you need a crude parachute more than an accurate altimeter.”

Funny how Daly and Curry both address the huge issues of uncertainty and complexity and arrive at diametrically opposed strategies of dealing with them. In terms of public communication, I’m with Daly.

From the principles governing IPCC work:

The role of the IPCC is to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation.

IPCC reports should be neutral with respect to policy, although they may need to deal objectively with scientific, technical and socio-economic factors relevant to the application of particular policies.

Funnily enough, a commenter at Judith’s, Paul in Sweden, took this as proof of a “blatantly biased agenda”. Which is a little strange in light of the history of climate science and of the IPCC as mentioned above. Its mandate is a consequence of the scientific evidence for human induced climate change having become increasingly strong and societally relevant. It doesn’t state what the conclusion ought to be –it has to follow the science-, but of course it states what it’s supposed to assess.

Judith Curry also seems to suggest that the IPCC reports are working towards a predetermined conclusion, when she claims that they are akin to a legal brief (meant to persuade). If true, that should be reflected by large differences between the scientific evidence and the IPCC reports, and between scientists’ opinions and the IPCC reports.  I have not seen evidence of either.

Tom Curtis made some very thoughtful comments on the consensus thread at Judith’s, e.g.

In other words, the IPCC was tasked with reporting the consensus view of the science, were such a consensus existed; and to explain and report the differing opinions where no such consensus existed. Whether they have done that is not best judged by whether they have explained and included the opinions of every crackpot fringe group with an axe to grind on global warming; nor even those of every climatologist, no matter how small a number might support their views. Rather, they are to be judged by the agreement between the IPCC reports and the known consensus and divergences of scientific opinion.

Fortunately, we have available several anonymous surveys of the scientists opinions, which show conclusively that the IPCC reports fairly represent the consensus of relevant scientists on those topics on which it reports. (…)

The purpose of IPCC is to provided as succinctly as possible the best possible scientific advice for policy deciders to operate on. If they were required to consider all and every idea on climate change that circulates on the blogosphere; then the resulting document would be to large, and to ill organised to be usefull as a guide to policy.

Nevermind that the politicans still wouldn’t have a clue as to what is more likely true. The science has to be assessed and weighted; that is what makes the IPCC process useful. There already is another outlet for every crackpot idea out there (NIPCC report); it doesn’t need to be done by the IPCC as well.

To quote the Dutch newspaper “Volkskrant” again:

its work has political implications, but that that doesn’t mean that it’s engaged in doing politics.

And since I discussed history as well, see also my first blog post where I described the IPCC process. I don’t think anyone has read it yet, so I’d be much obliged. And while doing self-promotion, I kind a like this oldie featuring Fred Singer.

Web-iquette for climate discussions

When checking some odd stuff regarding taking care of our 3 year old, I came across this web-iquette for discussing your internet search results with the doctor. Many of the same principles apply to a layperson browsing the web about climate change, which inevitably raises questions about what is true and what isn’t. The list bears some resemblance to my effort at providing hints for how to distinguish sense from nonsense in the climate change ‘debate’ (or other complex scientific issues such as health).

Now I’m a bit of an internet-doctor myself, so it’s useful mirror to look into. The list is as follows (replace “doctor” by “scientist” for more climate relevance):

1. Do bring it up. “Most doctors don’t see your research as an attempt to second-guess them.” (as long as you don’t accuse them of being a bunch of frauds, of course)

2. Keep the tone conversational, not confrontational. It sounds so sensible, yet so many people offend this very basic rule of human interaction. Me too, more often than I want to. Tell us that the science is just garbage, and we’ll stop listening to you very quickly. Or we’ll tell you to bugger off, if we’re in a bad mood and forget about this rule ourselves. Usually with a reference to a link or two.

3. When you get a diagnosis, ask the doctor to spell it.
A-n-t-h-r-o-p-o-g-e-n-i-c  G-l-o-b-a-l  W-a-r-m-i-n-g.

4. Check who’s behind the site. ”Falling for information from untrustworthy sources is the biggest mistake parents laypeople make. “Anyone can set up a site called the National Association for Such-and-Such,” pediatrician Alanna Levine notes. Check the “about us” section to see if the information was written or vetted by doctors scientists. Look for sites from government agencies (look for the .gov at the end of the link), universities (look for the .edu ending), or medical scientific organizations such as the American College of Obstetrics and Gynecology IPCC or the American Academy of Pediatrics NOAA, KNMI, etc.”

5. Don’t confuse personal experience with science. Anyone can write anything on the internet. Beware, it’s a dangerous place. And, don’t confuse weather with climate. Please. It’s making us soooooo tired.

6. Don’t assume your doctor has blown it based on what you read. Proclaiming that the science is all garbage just because you know how to use google does not impress anyone. Please refrain from doing so, it just makes you look silly. And if you’re really convinced of yourself, why don’t you submit your ideas to Science or Nature?

7. Let your doctor help you evaluate what you find. “There’s something to be said for a professional (such as a scientist) who has a base of knowledge and can help you sort through your own research,” says pediatrician Joseph Kahn. A doctor scientist can help you determine if the site is trustworthy (…) and if the information you found is outdated.” Expertise matters. You wouldn’t let your accountant do the plumbing and your plumber file your taxes, right?

8. Realize no doctor can read every single study the moment it comes out. “Medicine Science is constantly evolving”. Though that doesn’t usually mean that everything we know today will be invalid tomorrow. The big picture only changes very slowly.  Eat and drink in moderation and varied, and get enough exercise. More greenhouse gases in the air cause more warming. It’s been pretty stable advice/science for a while. Details may shift (is coffee good or bad for you? How important is aerosol nucleation for climate?), but the big picture less so.

9. Definitely ask about what’s confusing or troubling you. Asking, yes. Bringing up doubts, fine. Rational discussion, absolutely. Accusations of fraud, claiming that we just want to steal your SUV, nah.

Btw, it’s Blog Action Day! (with climate change as its theme.) Check out some of the links if you’re interested in more climate related blogs.

Who to believe?

 

Amidst all the different information about climate change, how is a layperson going to know who is right? There are a few clues one could follow, that don’t require any specialized knowledge.

 

–          Seeing the forest for the trees. Nitpicking on small details, and then claiming or insinuating that this challenges the foundation of a whole scientific field. Over-interpreting the significance of a specific finding. This is by far the most prevalent style of argument that one has to watch out for. It usually goes something like “This particular study proves that global warming isn’t due to greenhouse gases”. People tend to forget that observing a bird in the sky doesn’t disprove gravity.

–     Consensus matters. If you get a second opinion on your health condition, and it confirms what your specialist said in the first place, your trust in the diagnosis probably increases. Now imagine that you collect the interpretations of medical professionals all over the world, and by and large they their conclusions converge to the same broad picture. This happens to be how the IPCC comes to its conclusions. If the professionals do their work seriously, than the existence of a consensus amongst them is absolutely relevant (though of course it is not absolute proof). The only way in which you can ignore a consensus as being irrelevant, is if you can somehow show that the professionals are all lying or incompetent. (See the next clue for what that brings you into.) Oreskes has an excellent presentation on this.

–          Beware of conspiracy theories. The consensus wouldn’t matter if somehow all those scientists had bought into the same conspiracy of wanting to take away your SUV. (Don’t laugh, there are many people who seem to think this way.)

–          Timescales. Climate is defined as the average weather over 30 years. (Year-to-year variability usually averages out over 30 years). Weather and climate are very frequently confused in the popular debate.

–          Spatial scales. Combined with the previous one, an example would be: “It was a very cold winter in the US this year (so global warming is a farce)”. This is also used the other way around: “It was a very warm winter in the US this year (so global warming is getting worse)”. Both are equally silly conclusions.

–          Logic. Some of the most heard ‘skeptical’ arguments don’t stand up to basic logic, and no knowledge of climate is needed to see that. Example: “Climate has always changed, so it is not caused by humans.” It wasn’t in the past, but that’s no evidence that it isn’t now. Try that line of argument in a court of law against a pyromaniac, by saying that forest fires have always happened naturally; it won’t fly.

–          Confusion of cause and effect. A consensus emerged as a result of the strength of the accumulated evidence, not the other way around. Activists may try to persuade you to trade in your SUV for a Prius because they’re worried about climate change; not the other way around. A tricky one is temperature and CO2: They influence each other both ways. (see also here) 

–          Think in terms of likelihood. How likely is the previous proposition of a mass conspiracy amongst stubborn scientists? How likely is it that scientists have for decades overlooked this little finding that supposedly shakes the foundations of a relatively well established science?

–          Think in terms of risk. What if we take measures against global warming and it turns out less bad than expected? What if we don’t take measures against global warming and it turns out worse than expected? (False positive and false negative, respectively. See also this comment at RealClimate) 

–          Check for consistency. If someone sais (rightfully) that one particular event (e.g. Kathrina) is not proof of man-made climate change, but then claims that the current cold winter is proof against, you should raise your eyebrows.

–          Expertise. In gauging the credibility of a source, their expertise is important to consider. When it concerns your health, you usually trust a doctor’s opinion more than that of a software engineer. It is not unreasonable to trust a climate scientist more than a doctor when it concerns climate. Of course this is not proof, but there is a difference in likelihood of them knowing what they’re talking about.

–          Motive. The credibility of a source also depends on their motives, both on economic and ideological grounds, for telling you a certain side of the story. What vested interests, if any, are there to the different sides of the story? In a worldview where government interference is deeply hated, could it be tempting to distort evidence that could possibly lead to calls for government action? In a worldview where societal problems are preferably tackled by government, does it make any sense to make up a phony problem to call for government action? I don’t know anyone who wants government action on a phony problem just for the sake of it. Don’t underestimate the power of ideology, but always include a sanity check. See also here and here.

 

This list is not exhaustive, so if you have other pointers to add to make sense of the public debate on climate change, please share them in a comment. Similar issues of weeding through sources have been discussed in a number of thoughtful posts here, e.g. this one on cherry picking. Other good discussions here, here and here.

 

Ideally, you would critically assess the evidence for each position to form a well founded opinion on anthropogenic global warming (AGW). In the absence of time to do so, you need to take some shortcuts to assess the flood of information about the topic. None of the clues discussed here constitute proof for or against AGW, but applying multiple clues simultaneously to gauge the credibility of a source can be helpful to ‘distinguish the chaff from the grain’ (het kaf van het koren te scheiden, as we say in Dutch).

 

How do we know there’s a consensus, and why does it matter?

Investigating the consensus

In a study of over 900 scientific articles that had the keywords “climate change”, Oreskes found none (!) that disagreed with the consensus position (see here). That doesn’t mean that there weren’t any articles promoting a different view than the consensus position. (Articles that didn’t have the keyword “climate change” in their listing were not included in Oreskes’ review after all.) I’ve read quite a few papers myself that oppose the consensus view. But they can hardly be very many, relatively speaking. Otherwise Oreskes’ review would not have resulted in zero “skeptical” articles.

Almost all relevant scientific organizations and National Academies of Science endorse the consensus view that recent climate change is for a large part due to human activity. Even the most recent statement from the organization of petroleum engineers (!) acknowledges that recent climate change is linkes to human activity. A large scale review of the scientific literature, undertaken and endorsed by many, many scientists working in the field, is more trustworthy than any individual’s book or article or website. (Yes, that includes this one. You’ll get the most complete and balanced picture of climate change by reading the IPCC reports)

A recent survey of scientists having authored a recent journal article on climate change found that the majority concurred with the IPCC position. A sizeable minority was of the opinion that the IPCC reports overstate the importance of and/or certainty regarding CO2 compared to other forcings (both natural and anthropogenic!). Only very few respondents were of the “skeptical” opinion that warming is predominantly natural. Nobody denied that the globe is warming. A large minority found the IPCC too cautious, understating the human influence on climate and/or the seriousness of the problem. Note that the authors do not claim that their survey is representative; less then 10% of the 1800 scientists contacted replied. Moreover, the positions that respondents had to choose between were sometimes a little ambiguous.

In an excellent presentation, Naomi Oreskes provides an overview through history to show that this consensus is actually much older than the IPCC process; the IPCC was set-up in response to the growing consensus that emerged in the late seventies. And already before World War II global warming was recognized by individual scientists. This begs the question why it takes society so long to recognize the problem, and do something about it? The second half of her presentation (similar powerpoint presentation here), Oreskes explains one of the reasons why: A successful campaign to create doubt in people’s minds about the reality of climate change, along similar lines (and starring some of the same people) as the campaign to downplay the risks of smoking. See also here and here.

 

Proof versus probability

Does having a broad consensus automatically make something true? No. Is there absolute proof that the climate is changing, that it is predominantly caused by human activity, and that the consequences will be severe? No, there is not (at least not in the absolute, mathematical sense). Do we need proof? If yes, then we have to wait until the disaster strikes, and even then we cannot possibly prove the abovementioned claims. If a plane technician tells you that there is a 75% chance that the plane you are about to board will crash, would you board the plane? Would your action (presumably of not boarding) change if an economist points you to some screws in the wing of the plane that are perfectly in place, telling you that he therefore concludes that he regards it as totally save to board the plane? What if 99 engineers tell you it is unsafe and one tells you it is safe?

Everybody makes decisions each day based on an assessment of the probability of something happening, and the consequences (positive and negative) of when it happens. Governments make policy based on such probabilities. Many of these probabilities are much weaker constrained by scientific knowledge than climate change is.

How many types of insurance do you have? You have these not because accidents are so likely to happen, but often because the effects if they happen are severe. With unmitigated climate change, not only are the effects potentially severe, but the chance of severe consequences is rather high. Isn’t that worth insuring ourselves against? Isn’t that worth serious attempts to decrease the likelihood of those consequences materializing? If you want proof, please go and find yourself another planet to play Russian roulette with. Go and board that plane. But don’t force me and my children to join you. I better be safe than sorry.

 

Scientific Progress

Scientific progress is a usually a gradual process. “Skeptics” and their supporters often bring up Galileo as an example of that the scientific consensus can also be wrong, and has been wrong in the past. True enough, but for every Galileo there probably are thousands of “fossil fools”. Actually, the theory that increasing the concentration of greenhouse gases could influence the climate was perceived as wildly strange and improbable at the time of its first proposition (late nineteenth century). But rather than that one person suddenly overturned current wisdom, it is a matter of accumulating evidence by many scientists over a long time period that gradually changes and sharpens the scientific picture of what is happening. That is typically how scientific progress works these days: cumulative, piece by piece. The likelihood that a tiny minority of scientists, or some new piece of evidence, radically alters this picture is very small indeed. New evidence has to be reconciled with the existing mountain of evidence; it doesn’t simply replace it. Observing a bird in the air doesn’t disprove gravity. Small changes here and there in our understanding of specifics, that happens all the time. That’s how the mountain of evidence has been built in the first place, and that is how it continues to be shaped. That’s science at work.

 

What if the consensus is wrong?

The only way in which the consensus view could be “wrong” is that the effect of greenhouse gases on climate is smaller than currently thought. No warming effect from greenhouse gases at all is physically impossible (the earth would be 30 degrees colder than it currently is if there were no greenhouse effect). If warming will be less severe, it means that we have some more time to take serious action; not that we can forget about doing anything about it. It reminds me of a guy’s t-shirt I once saw with the text: “Sex is like pizza. If it’s good, it’s really good. If it’s bad, it’s still pretty good”. Well, perhaps we could say that “Climate change is like Brussels sprouts. If it’s bad, it’s really bad. If it’s good, it’s still pretty bad”.

If the contribution from greenhouse gases to climate change is smaller and the contribution from natural sources is larger than currently thought, we would have to curtail their emissions even more to stabilize the climate. If a situation is undesirable (global warming), you should change the things you can (greenhouse gas emissions), and accept the things you cannot change (the sun). Not reducing our greenhouse gas emissions is simply not an option.

Fossil fuels are finite, and it is only a matter of time that the oil production will start to decline. We will have to develop alternative energy sources. There is still plenty of coal, but the air pollution that it causes is reason enough to curtail its use. Already now hundreds of thousands of people die prematurely from air pollution. The CO2 that is emitted form fossil fuel burning causes the oceans to become more acidic, with potentially severe consequences for ocean life and fisheries. There are also geo-political reasons to want to become less reliant on fossil fuels, and oil in particular. Reducing our greenhouse gas emissions by changing our energy system and agricultural practices does not only cost money; it also creates (economic) opportunities. There will be winners and losers. The ones foreseeing that they’re losing are often the ones claiming the loudest that climate change is not occurring, or is natural, or even beneficial. All in all, developing alternative energy sources makes a lot of sense for many other reasons than climate change.

 

What if the consensus is right?

That one’s easy. We better be happy that we started reducing our greenhouse emissions soon and strongly. Act and vote accordingly. And don’t move to the Netherlands, as I did.

 

Final remarks

Which situation would you be rather in: Having reduced our greenhouse gas emissions when later it appears that global warming is not as severe as expected, or not having reduced our greenhouse gases when later it appears that global warming is even more severe than expected?