Science & Nature

Climate scientists speak to us. What is their consensus opinion?

Summary: Senator Kerry kicked off the Obama administration’s campaign for policy action to fight climate change. He referred to the oft-cited 97% consensus of scientists. Since it is the basis for large and expensive policy proposals, we should know exactly what is the consensus. Here we look at the studies producing that widely cited number.

The Consensus Project

The second line is false, “a” cause not “the” cause.


Secretary of State Kerry provides a clear example what is by now a standard play by US leaders: attempting to spark public action by exaggerating  a threat.  In this case, global warming and the resulting climate change. He gave a common but inaccurate description of the current state of climate science — exaggerating the certainty of scientists ab0ut the imminence and magnitude of the threat.

Here we compare Kerry’s words with the actual research showing the consensus. They do not match closely. The graphic at the right shows an example. Global warming is happening, but these surveys do not show agreement that “we are the cause” (rather, we are “a” cause).

However, Kerry’s misrepresentations probably will not matter. Generations of such propaganda have left the American public apathetic, our spiritual adrenal glands exhausted from over-stimulus. Only a generation or so of cold unvarnished truth can restore our ability to adequately see and assess threats. Restoring confidence in the honesty of our leaders will take longer.

“Mr. President, if that’s what you want there is only one way to get it.  That is to make a personal appearance before Congress and scare the hell out of the country.”
— Senator Arthur Vandenberg’s advice to Truman about starting the Cold War.  On 12 March 1947 Truman did so.  From Put yourself in Marshall’s place, James P. Warburg (1948); in 1941 Warburg helped develop our wartime propaganda programs.

Time: Global Warming

A slight exaggeration. Time, 9 April 2001.


Excerpt from remarks on Climate Change

Speech by Secretary of State John Kerry
Jakarta, Indonesia 16 February 2014

So when thousands of the world’s leading scientists and five reports over a long period of time with thousands of scientists contributing to those reports – when they tell us over and over again that our climate is changing, that it is happening faster than they ever predicted, ever in recorded history, and when they tell us that we humans are the significant cause, let me tell you something: We need to listen. When 97% of scientists agree on anything, we need to listen, and we need to respond.

  1. These scientists agree on the causes of these changes and they agree on the potential effects.
  2. They agree that the emission of greenhouse gases like carbon dioxide contributes heavily to climate change.
  3. And they agree that, if we continue to go down the same path that we are going down today, the world as we know it will change – and it will change dramatically for the worse.

There is no basis for much of this, as Kerry grossly exaggerates the extent of the consensus among climate scientists. Most of these assertions appear in the IPCC’s reports, but with widely varying confidence levels.  Stating these as certainties converts them from conclusions of scientific research into Leftist propaganda, made truth in their followers’ minds through endless repetition.

Let’s look at one claim, in a sense the foundation for the speech. What is the basis for the 97% number Kerry cites? First, a reminder of the actual consensus of climate scientists. The surveys shown below show strong agreement with this key statement by the IPCC; none show agreement beyond it.

“It is extremely likely (95 – 100% certain) that human activities caused more than half of the observed increase in global mean surface temperature from 1951 to 2010.”
— conclusion of the IPCC’s AR5 Working Group I. See some of the research about the 1950 start date here.

Now let’s look at the research defining the consensus. None of these studies show the boundaries of consensus among climate scientists, or the fault lines of disagreement within the field (that’s not their objective). All show agreement with the IPCC keynote finding. None show agreement with the claims made by Kerry.

(1) Examining the Scientific Consensus on Climate Change“, Peter T. Doran and Maggie Kendall Zimmerman, EOS, 20 January 2009 — They ask a question of little relevance to the current policy debate, followed by a uselessly vague question. The second question does not state what time period it refers to (there is no basis in the climate science literature for attributing the temperature increase before WW2 to anthropogenic factors).

Newsweek: global warming hoax

Article about crazy people, Newsweek, 13 August 2007.

Also, a sample of 79 scientists is too small to be meaningful. Thousands of scientists have written about climate change, although they classify their specialty in many ways (there were few, if any, degrees awarded in “climate science” before the 1990).

Excerpt (red emphasis added):

Q1: “When compared with pre-1800s levels, do you think that mean global temperatures have generally risen, fallen, or remained relatively constant?” 76 of 79 (96.2%) answered “risen.”

Q2: “Do you think human activity is a significant contributing factor in changing mean global temperatures?” 75 of 77 (97.4%) answered “yes.”

… In our survey, the most specialized and knowledgeable respondents (with regard to climate change) are those who listed climate science as their area of expertise and who also have published more than 50% of their recent peer-reviewed papers on the subject of climate change (79 individuals in total). Of these specialists, 96.2% (76 of 79) answered “risen” to question 1 and 97.4% (75 of 77) answered yes to question 2.

(2) Quantifying the consensus on anthropogenic global warming in the scientific literature“, John Cook et al, Environmental Research Letters, 22 April 2013 — Amateurs, readers of Cook’s website (i.e., strong believers in catastrophic anthropogenic climate change), classified papers on the following grid. This is an elaborate but amazingly poorly conceived poll. For example, the questions do not specify a time period for the warming: last decade, last century, last millennium, etc.

As with the Doran paper, the results are consistent with the IPCC’s statement, but tell us nothing more.


Quantifying the consensus on anthropogenic global warming in the scientific literature, Cook 2013. Click to enlarge.

An important caveat to the results, adding a degree of subjectivity to Table 2:

“To simplify the analysis, ratings were consolidated into three groups: endorsements (including implicit and explicit; categories 1–3 in table 2).”

(3)  One of the two surveys asking a useful question:  “Is there agreement amongst climate scientists on the IPCC AR4 WG1?“, Fergus Brown, Janes Annan, and Roger Pielke Sr., unpublished, 2008 — Results of a non-randomized online poll of scientists:

  1. The largest group of respondents (45-50%) concur with the IPCC perspective as given in the 2007 Report.
  2. A significant minority (15-20%), however, conclude that the IPCC understated the seriousness of the threat from human additions of CO2.
  3. A significant minority (15-20%), in contrast, conclude that the IPCC overstated the role of human additions of CO2 relative to other climate forcings.
  4. Almost all respondents (at least 97%) conclude that the human addition of CO2 into the atmosphere is an important component of the climate system and has contributed to some extent in recent observed global average warming.

(4) The Structure of Evolving US Scientific Opinion on Climate Change and its Potential Consequences“, Stephen J. Farnsworth and Samuel Robert Lichter, APSA 2009 Toronto Meeting Paper. As usual, it does not distinguish between the largely natural pre-1950 warming and the post-1950 warming (per the IPCC, more than half of the warming being anthropogenic).


The Structure of Evolving US Scientific Opinion on Climate Change and its Potential Consequences, Farnsworth 2009.

(5)  Also asking a useful a precise question: “Expert credibility in climate change“, William R. L. Anderegg et al, Proceedings of the National Academy of Sciences, online only, 21 June 2010 —

Here, we use an extensive dataset of 1,372 climate researchers and their publication and citation data to show that

  1. 97–98% of the climate researchers most actively publishing in the field support the tenets of ACC (anthropogenic climate change) outlined by the Intergovernmental Panel on Climate Change, and
  2. the relative climate expertise and scientific prominence of the researchers unconvinced of ACC are substantially below that of the convinced researchers.

(6)  Meteorologists’ views about global warming: A survey of American Meteorological Society professional members“, Neil Stenhouse et al, Bulletin of the American Meteorological Society, July 2014 — “in January 2012 we surveyed all AMS members with known email addresses, achieving a 26.3% response rate.”

This shows a wide range of opinions, perhaps because they interpret the question in different ways — as practicing meteorologists often focus on different time horizons, from immediate to historical. For example, the pause in warming of the surface air temperature can mean that “global warming” is not happening “now”.

AMS survey

Meteorologists’ views about global warming.

(7) Scientists’ Views about Attribution of Global Warming“, Bart Verheggen, Environmental Science & Technology, 19 August 2014 — Figure 2 is a more precise representation of the IPCC’s consensus statement. ~75% of scientists surveyed believe that over half of warming since 1950 results from anthropogenic factors.

ESL: Climate science consensus

Percentages for the contribution of anthropogenic GHG to global warming since the mid-20th century (Q1). Responses are shown as a percentage of respondents (N) in each subgroup, segregated according to self-declared (SD) fields of expertise “WG1” (categorized as Working Group 1) and “attractor” (expertise in attribution or aerosols and clouds).

(8) The climate change consensus extends beyond climate scientists” by J S Carlton et al, Environmental Research Letters, October 2015. Abstract:

The existence of anthropogenic climate change remains a public controversy despite the consensus among climate scientists. The controversy may be fed by the existence of scientists from other disciplines publicly casting doubt on the validity of climate science. The extent to which non-climate scientists are skeptical of climate science has not been studied via direct survey. Here we report on a survey of biophysical scientists across disciplines at universities in the Big 10 Conference.

Most respondents (93.6%) believe that mean temperatures have risen and most (91.9%) believe in an anthropogenic contribution to rising temperatures. Respondents strongly believe that climate science is credible (mean credibility score 6.67/7). Those who disagree about climate change disagree over basic facts (e.g., the effects of CO2 on climate) and have different cultural and political values. These results suggest that scientists who are climate change skeptics are outliers and that the majority of scientists surveyed believe in anthropogenic climate change and that climate science is credible and mature.

(9) Misstating the 97% consensus

It’s become trendy to state that 97% of scientists believe whatever is convenient to say at that moment — making up results. Even NASA does it:

97% of climate scientists agree that climate-warming trends over the past century are very likely due to human activities, and most of the leading scientific organizations worldwide have issued public statements endorsing this position.

None of the statements they cite say “over the past century”. Rather they mirror the IPCC statement, speaking of “past 50 years”, “past few decades”, or “or since mid-20th century”. It’s an important point, since the century of prior natural warming comprises much of the warming since the end of the Little Ice Age, that often cited as “global warming”. Recognition of the natural warming refutes the common implication that the natural climate is stable.

(9)  Other Research

See the Wikipedia entry  Surveys of scientists’ views on climate change

Death world

From the Australian Broadcasting Co, 13 Dec 2011.

(10) Comments about Kerry’s speech

(a) By Judith Curry (Prof Atmospheric Science, GA Institute Technology)

{Kerry}  has also over interpreted the confidence of the IPCC findings.   There is one statement I agree with: “The solution to climate change is as clear as the problem.” The climate change problem is not at all clear, especially with regards to impacts, and the solutions are even less clear.

(b) Seeking the Strategy Behind Kerry’s Climate Speech in Indonesia“, Andrew C. Revkin, blog of the New York Times, 17 February 2014 — Opening:

I’m hoping that someone can identify some smart strategic angle behind Secretary of State John Kerry’s climate speech in Jakarta on Sunday pressing Indonesia, in essence, to forsake its ample reserves of fossil fuels in its push to develop its economy. I can’t.

(c) Why Kerry Is Flat Wrong on Climate Change“, McNider and Christy, op-ed in the Wall Street Journal, 19 February 2014 — “It was the scientific skeptics who bucked the ‘consensus’ and said the Earth was round.”

(11)  For More Information

(a) Articles by Judith Curry (Prof Atmospheric Science, GA Institute Technology) about the nature of consensus in science:

  1. About the 97% consensus: Part One and Part Two
  2. Climate change: no consensus on consensus“, J. A. Curry, and P. J. Webster, CAB Reviews, February 2013 — “This essay explores the history and consequences of scientific consensus building activities by the IPCC.” Gated. Open copy here.

(b)  Wonderful example of hysterical climate alarmism and denial of climate science (see below): “Planet, Oceans Burning Up: There is no “Pause” in Global Warming” by Jon Queally at informed COMMENT, 13 February 2014.

(c)  A note from the past, since climate alarmism is always in season: “Winter in New York: Something’s Missing; Absence of Snow Upsets Rhythms Of Urban Life and Natural World“, New York Times, 15 January 2000 — Excerpt:

”I bought a sled in ’96 for my daughter,” said Dr. Michael Oppenheimer, a scientist at the nonprofit Environmental Defense Fund. ”It’s been sitting in the stairwell, and hasn’t been used. I used to go sledding all the time. It’s one of my most vivid and pleasant memories as a kid, hauling the sled out to Cunningham Park in Queens.”

At least part of the reason for the recent warm winter is La Nina … This has been allowing space for warm winds from the south to expand into the Northeast, including New York. And Dr. Oppenheimer, among other ecologists, points to global warming as perhaps the most significant long-term factor.

(d)  Charles Pierce, Esquire, 17 February 2014:

This week, a Very Special Episode of How We’re Fked As A Species. Centuries from now, when the several remaining humans are huddled around a dwindling fire and pondering how each of them will kill the others and eat their still-warm flesh, the most boring among the remnant will pose the question, “Who is to blame for all of this?” Someone will mention the Koch Brothers. Someone else will bring up BP, and maybe our old friend, the Keystone XL pipeline will get a moan-out while the silent one in the corner sizes up the available rocks and studies the heads of his companions.

Truth Will Make You Free

For More Information

(a) Reference Pages about climate on the FM sites:

  1. The keys to global warming.
  2. Studies & reports, by subject.
  3. My posts about climate change.
  4. See all posts about the pause.




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