New survey reconfirms overwhelming scientific consensus on AGW

mentalfloss

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Survey confirms scientific consensus on human-caused global warming

A survey among more than 1800 climate scientists confirms that there is widespread agreement that global warming is predominantly caused by human greenhouse gases.
This consensus strengthens with increased expertise, as defined by the number of self-reported articles in the peer-reviewed literature.
The main attribution statement in IPCC AR4 may lead to an underestimate of the greenhouse gas contribution to warming, because it implicitly includes the lesser known masking effect of cooling aerosols.
Self-reported media exposure is higher for those who are skeptical of a significant human influence on climate.
In 2012, while temporarily based at the Netherlands Environmental Assessment Agency (PBL), my colleagues and I conducted a detailed survey about climate science. More than 1800 international scientists studying various aspects of climate change, including e.g. climate physics, climate impacts and mitigation, responded to the questionnaire. The main results of the survey have now been published in Environmental Science and Technology (doi: 10.1021/es501998e).

Level of consensus regarding attribution

The answers to the survey showed a wide variety of opinions, but it was clear that a large majority of climate scientists agree that anthropogenic greenhouse gases are the dominant cause of global warming. Consistent with other research, we found that the consensus is strongest for scientists with more relevant expertise and for scientists with more peer-reviewed publications. 90% of respondents with more than 10 climate-related peer-reviewed publications (about half of all respondents), agreed that anthropogenic greenhouse gases (GHG) are the dominant driver of recent global warming. This is based on two different questions, of which one was phrased in similar terms as the quintessential attribution statement in IPCC AR4 (stating that more than half of the observed warming since the 1950s is very likely caused by GHG).



Figure 1. The more publications the respondents report to have written, the more important they consider the contribution of greenhouse gases to global warming. Responses are shown as a percentage of the number of respondents (N) in each subgroup, segregated according to self-reported number of peer-reviewed publications.

Literature analyses (e.g. Cook et al., 2013; Oreskes et al., 2004) generally find a stronger consensus than opinion surveys such as ours. This is related to the stronger consensus among highly published – and arguably the most expert – climate scientists. The strength of literature surveys lies in the fact that they sample the prime locus of scientific evidence and thus they provide the most direct measure of the consilience of evidence. On the other hand, opinion surveys such as ours can achieve much more specificity about what exactly is agreed upon and where the disagreement lies. As such, these two methods for quantifying scientific consensus are complementary. Our questions possibly set a higher bar for what’s considered the consensus position than some other studies. Furthermore, contrarian viewpoints were likely overrepresented in our study compared with others.

No matter how you slice it, scientists overwhelmingly agree that recent global warming is to a great extent human caused.




Figure 2. The more publications the respondents report to have written, the more they agree with greenhouse gases being the main contributor to global warming (red bars). IPCC AR4 authors report the most agreement with GHG-driven global warming. Results are based on two different questions, one about the qualitative contribution of GHG (Q3) and one about the quantitative contribution of GHG (Q1).The latter question resulted in more “undetermined” answers (unknown, I don’t know, or other), presumably because it was more difficult to answer. Hence the percentage of consensus can best be compared by excluding these “undetermined” answers. Responses are shown as a percentage of the number of respondents in each subgroup.

The concept of ‘consensus’ has been discussed a lot lately. Whereas the presence of widespread agreement is obviously not proof of a theory being correct, it can’t be dismissed as irrelevant either: As the evidence accumulates and keeps pointing in the same general direction, the experts’ opinion will converge to reflect that, i.e. a consensus emerges. A theory either rises to the level of consensus or it is abandoned, though it may take considerable time for the scientific community to accept a theory, and even longer for the public at large.

Greenhouse warming versus aerosol cooling

By phrasing Question 1 analogously to the well-known attribution statement of AR4 we found something peculiar: Respondents who were more aware of the cooling effect of aerosols in greater numbers assessed the greenhouse gas contribution to recent warming to be larger than the observed warming (consistent with the IPCC assessments). We concluded that the AR4 attribution statement may lead people to underestimate the isolated greenhouse gas contribution. The comparable AR5 statement is an improvement in this respect.

Media exposure

Respondents were also asked about the frequency of being featured in the media regarding their views on climate change. Respondents who thought climate sensitivity was low (less than 1.75 degrees C per doubling of CO2) reported the most frequent media coverage. Likewise, those who thought greenhouse gases had only made an insignificant contribution to observed warming reported the most frequent media coverage. This shows that contrarian opinions are amplified in the media in relation to their prevalence in the scientific community. This is related to what is sometime referred to as “false balance” in media reporting and may partly explain the divergence between public and scientific opinion regarding climate change (the so-called “consensus gap”).



Figure 3. The most frequent media coverage is reported by respondents who estimated climate sensitivity to be lowest (<1.75 degrees for a doubling of CO2 concentration). Respondents are grouped according to their estimate of climate sensitivity (colored bars). Responses are shown as a percentage of the number of people (N) in each climate sensitivity range.

Survey respondents

Respondents were selected based on a few criteria: Having authored articles with the key words ‘global warming’ and/or ‘global climate change’, covering the 1991–2011 period via the Web of Science. This is the same database used by Cook et al in their recent ERL study (PS: John Cook is co-author on this current study as well). Respondents were also selected based on inclusion in the climate scientist database assembled by Jim Prall, as well as by surveying the recent climate science literature. Prall’s database includes signatories of public statements disapproving of mainstream climate science. They were included in our survey to ensure that the main criticisms of climate science would be included. This last group amounts to less than 5% of the total number of respondents, about half of whom only published in the gray literature on climate change.

Survey questions

Detailed questions were posed about a variety of physical climate science issues, which are discussed in the public debate about climate change. Answer options reflected a variety of viewpoints, all of which were phrased as specific and neutral as possible. Before executing the survey, questions and answers (pdf) were reviewed by physical and social scientists and climate change public commentators with a wide range of opinions (see acknowledgements for a list of names), to minimize the chance of bias.

Comments on the survey by respondents varied: some said it was slanted towards the ‘alarmist’ side (“Obviously these questions were posed by warmists”), but more respondents commented that they thought it was slanted towards the ‘skeptical’ side (“I suspect this survey comes from the denial lobby”).

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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. The article is open access.

An FAQ for this article is here.

Survey confirms scientific consensus on human-caused global warming | My view on climate change
 

captain morgan

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A survey among more than 1800 climate scientists confirms that there is widespread agreement that global warming is predominantly caused by human greenhouse gases.
This consensus strengthens with increased expertise, as defined by the number of self-reported articles in the peer-reviewed literature.

So basically, there is a consensus among the true believers

Big time fail there champ
 

mentalfloss

Prickly Curmudgeon Smiter
Jun 28, 2010
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In the absence of any real proof, they qualify as faith-based, true believers

 

Locutus

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Jun 18, 2007
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there's a 'new survey', there's a 'new survey'!

I have a new thread, a new thread.

Ok Newton, now shut-up and bring me my shield! :lol:
 

mentalfloss

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

Posted on 11 August 2014 by Bart Verheggen
This is a repost from Bart Verheggen's blog.
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.



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-20th (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 approximately 3% 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.

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

mentalfloss

Prickly Curmudgeon Smiter
Jun 28, 2010
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67% of climate scientists didn't write papers that comment on the cause of climate change.

This is now the fifth time I've had to explain this to you.
 

mentalfloss

Prickly Curmudgeon Smiter
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Because they are aware of the Holocene.

No, it's because smaller geographic areas have their own climates and the scope of those papers didn't focus on global climate change.

It's like asking every biologist to comment on some characteristic of bees and saying there is no consensus because the vast majority do not specialize in that species' anatomy.