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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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The 97% consensus on global warming

What the science says...

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97% of climate experts agree humans are causing global warming.

Climate Myth...

There is no consensus

The Petition Project features over 31,000 scientists signing the petition stating "There is no convincing scientific evidence that human release of carbon dioxide will, in the forseeable future, cause catastrophic heating of the Earth's atmosphere ...". (Petition Project)

Science achieves a consensus when scientists stop arguing.  When a question is first asked – like ‘what would happen if we put a load more CO2 in the atmosphere?’ – there may be many hypotheses about cause and effect. Over a period of time, each idea is tested and retested – the processes of the scientific method – because all scientists know that reputation and kudos go to those who find the right answer (and everyone else becomes an irrelevant footnote in the history of science).  Nearly all hypotheses will fall by the wayside during this testing period, because only one is going to answer the question properly, without leaving all kinds of odd dangling bits that don’t quite add up. Bad theories are usually rather untidy.

But the testing period must come to an end. Gradually, the focus of investigation narrows down to those avenues that continue to make sense, that still add up, and quite often a good theory will reveal additional answers, or make powerful predictions, that add substance to the theory.

So a consensus in science is different from a political one. There is no vote. Scientists just give up arguing because the sheer weight of consistent evidence is too compelling, the tide too strong to swim against any longer. Scientists change their minds on the basis of the evidence, and a consensus emerges over time. Not only do scientists stop arguing, they also start relying on each other's work. All science depends on that which precedes it, and when one scientist builds on the work of another, he acknowledges the work of others through citations. The work that forms the foundation of climate change science is cited with great frequency by many other scientists, demonstrating that the theory is widely accepted - and relied upon.

In the scientific field of climate studies – which is informed by many different disciplines – the consensus is demonstrated by the number of scientists who have stopped arguing about what is causing climate change – and that’s nearly all of them.

Authors of seven climate consensus studies — including Naomi OreskesPeter DoranWilliam AndereggBart VerheggenEd MaibachJ. Stuart Carlton, and John Cook — co-authored a paper that should settle this question once and for all. The two key conclusions from the paper are:

1) Depending on exactly how you measure the expert consensus, it’s somewhere between 90% and 100% that agree humans are responsible for climate change, with most of our studies finding 97% consensus among publishing climate scientists.

2) The greater the climate expertise among those surveyed, the higher the consensus on human-caused global warming.

consensus studies

Expert consensus results on the question of human-caused global warming among the previous studies published by the co-authors of Cook et al. (2016). Illustration: John Cook.  Available on the SkS Graphics page

consensus vs expertise

Scientific consensus on human-caused global warming as compared to the expertise of the surveyed sample. There’s a strong correlation between consensus and climate science expertise. Illustration: John Cook. Available on the SkS Graphics page

Expert consensus is a powerful thing. People know we don’t have the time or capacity to learn about everything, and so we frequently defer to the conclusions of experts. It’s why we visit doctors when we’re ill. The same is true of climate change: most people defer to the expert consensus of climate scientists. Crucially, as we note in our paper:

Public perception of the scientific consensus has been found to be a gateway belief, affecting other climate beliefs and attitudes including policy support.

That’s why those who oppose taking action to curb climate change have engaged in a misinformation campaign to deny the existence of the expert consensus. They’ve been largely successful, as the public badly underestimate the expert consensus, in what we call the “consensus gap.” Only 16% of Americans realize that the consensus is above 90%.

Lead author John Cook explaining the team’s 2016 consensus paper.

 

Last updated on 8 May 2016 by BaerbelW . View Archives

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Further reading

Further viewing

The "Climate Denial Crock of the Week" video series examines the list of "32,000 leading skeptical scientists."

Naomi Oreskes gives a thorough presentation of the development of our scientific understanding of anthropogenic global warming:

Here is a video summary of the various studies quantifying the scientific consensus on human-caused global warming, as well as the misinformation campaigns casting doubt on the consensus.

Acknowledgements

Many thanks to Joe Crouch for his efforts in tracking down scientific organizations endorsing the consensus as well as links to their public statements.

Update

On 21 Jan 2012, we revised 'the skeptic argument' with a minor quote formatting correction.

Comments

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Comments 451 to 475 out of 802:

  1. Dana69, if I do some research, and independently come to the same conclusion as a great many scientists carrying out similar research before me, then I am following the consensus. I'm not doing it blindly, and I would be doing so absolutely based on my own views. Let's say, on the hypothesis that an apple released at shoulder height will go down, rather than up, I carry out the experiment. I find the same answer as the scientific consensus on the matter. Am I blindly following the consensus? When you (indirectly) accuse others of being sheep, be careful your argument is not wooly.
  2. I posted this on RealClimate a few days ago: "Los Alamos National Laboratory is hosting the Third Santa Fe Conference on Global and Regional Climate Change Oct. 31 thru Nov. 4. A lot of good science has come out of LANL, but the conference program is dismaying. I’m not familiar with many of the names on it, but I do know a few of them, e.g. Lindzen, Singer and Monckton! What can the conference organizers be thinking?" In response, Gavin pointed out that one of the organizers is Petr Chylek, who leads a Remote Sensing team at LANL. It appears Chylek is attempting to bolster the scientific credibility of AGW denial, as he has done this kind of thing before. His strategy may backfire, by diminishing LANL's reputation for producing high-quality science.
  3. From a debate on another thread where Jonathon argued: "For the record, I do not believe that a large range of values (whether it be climate sensitivity, projected warming, etc.) indicates that there is a consensus on the issue. On the contrary, it argues the opposite." I do think 'consensus' that some variable is changing can apply to a wide range of estimated values so long as that range does not include zero. There has been for many years a large range on estimated climate sensitivity (e.g. the oft-quoted 2C-4.5C per doubling CO2). I want to give another example where there was, for a great many years, a lot of uncertainty in the magnitude of a value, yet the existence of the change it implied was not questioned. For many years, there was a large range for estimated values of H0, the expansion rate of the Universe, which only recently has been narrowed down considerably. As recently as 1996, there were estimates as low as 40km/s/Mpc and as high as 100km/s/Mpc, it is now closer to 74km/s/Mpc. Edwin Hubble's initial estimate in 1929, after he first measured the redshift of spectral lines in Cepheid variables, was 500km/s/Mpc. Was there consensus in 1996 that the Universe is expanding? There certainly was. Was that based on a tightly-constrained value for the expansion rate? Absolutely not.
  4. Skywatcher, I disagree that just because a value is not zero, that there is a consensus among all players. Do you really believe that Lindzen, who published that the climate sensitivity is 0.5, Link - 1.1, Spencer - 1.3, Annan - 3, Hansen - 6, and Pagani - 9.4 are all in agreement? This seems odd to me, especially since there are many from this site who constantly argue against Lindzen and Spencer (and anyone else who claims a low climate sensitivity). Do you really believe that they are part of the "consensus" just because their values are nonzero?
  5. Jonathon The individual scientists may not agree on the most likely value of equilibrium climate sensitivity, but that does not mean there is not consensus on the distribution of plausible values for equilibrium climate sensitivity, which is what the IPCC actually presents. The scientists are well aware that there are different ways of estimating climate sensitivity and each will give a different answer, thus there is uncertainty involved, and there is no good reason to think of any of the point estimates as the truth, but instead look how the various estimate constrain the values that can be considered plausible according to what we do know. Of course Spencer won't agree, but that is becuase his estimate of climate senistivity lies outside the range considered plausible by the mainstream consensus view. Note Spencer would have a hard time explaining many paleoclimate events with such a low sensitivity, which is why the concenssu is that a value that ow isn't plausible.
  6. While I agree that there is agreement that CO2 has contributed to the observed warming (i.e. climate sensitivity is greater than zero), I disagree that there is agreement as to the value of the climate sensitivity. Posts made on the other thread claimed that any sensitivity greater than zero was part of a consensus about the climate sensitivity. There is little agreement on the range of climate sensitivity values (the most commonly quoted ranges are 2-4.5, 1.5-4.5, and 1.5-5). With the exception of James Annan, the five scientists I mentioned in my earlier post are all outside this range, and there are others which make claims of even higher and lower values. Sure, Spencer will not agree, but I doubt that Hansen will either. There appears to be a misconception on the other thread that since scientists agree that CO2 has contributed to warming, that there is a consensus as to how much.
  7. Jonathon If say Annan publishes an estimate of climate sensitivity of 3, that does not mean that he thinks Hansen's estimate of 6 (I'll take your word for it that is Hansens most probable value rather than a bound) is implausible, and vice versa. This is not at all unlikely as scientists know that estimates made via different methods, with different sources of uncertainty, will have different results, without that meaning that one s right and the other is wrong. It just means that the plausible range for the true value, given what we actually know, lies somewhere in beteen the two estimates. Thus they would have a concensus opinion that climate sensitivity lies in the range 3-6. As the new estimates are considered, if they are considered plausible (even if not very likely) then the concensus range will increase. The point is that the concensus is on the range of plausible values, not on the individual point estimates. This is actually a good way to narrow down the uncertainty of the estimate of climate sensitivity by performing research that places constraints on climate sensitivity, beyond which they are not plausible (or inconsistent with the observations). I rather suspect that the Pagani value for instance is not a estimate of the most likely value, but an upper bound resulting from some physical constraint. BTW, climate sensitivity is not specific to CO2 radiative forcing, it applies more or less equally to any other forcing.
  8. Dikran, Using ranges is a very good way to narrow down uncertainties in many instances. For such a complicated scenario, different methods are used in an attempt to ascertain the most likely value (or range of values). In genetics, significant research has been able to narrow down the genes responsible for specific traits. Initially, there would be no consensus, but as pieces were placed together, a general picture appeared, resulting in an agreement among the scientists involved. At some point, you could say a consensus occurs, because the scientists agree that certain genes are responsible, without nailing down the specifics. The point at which that occurs may be somewhat nebulous. The same could be said for climate science. At what point can we say there is a consensus on climate sensitivity? My conclusion is that the range is still too wide to claim a general agreement. Some have tried to narrow the range, but then lose enough scientists to preclude calling it a consensus. BTW, the Pagani value was determined from paleo measurements, and Hansen and Sato (2011) recently stated that fast climate sensitivity was 3, while equilibrium climate sensitivity was 6. Excluding the Pagani value, with may not e relevant to today anyway, to claim a consensus opinion on the range of climate sensitivity, one would have to choose values from ~1-7! IMO, this does not constitute a consensus.
  9. Jonathon As I said, there is a concensus, the concensus is on the range of plausible values because at this stage there is insufficient evidence to make a stronger statement given out current state of knowledge. Of course there is no agreement on a specific value for climate sensitivity, nobody is claiming that there is, and indeed it is an unreasonable expectation. However that doesn't mean we can't have a concensus on the spread of plausible values. Note that a spread of plausible values is what we need for impacts studies, so that the distribution of plausible loss properly incorporates our uncertainty regarding climate sensitivity. You need to get away from the idea that we need to know the exact value of climate sensitivity. I note that your comment regarding the Pagani value does not address the question as to whether it is a most probable value or a bound.
  10. Dikran, I guess it comes down to what we understand to be the range of plausible values, and if that range is sufficient to state that there exists a consensus. I am not comfortable making that claim at this time, as I would prefer to see a narrower range of plausible values before making that assertion. Also, I do not believe that scientists would agree on the range. This does not mean that a consensus could not be formed in the future. I do not need to know the exact value, but the concept that the high end of the range is a factor of three higher than the low end implies that we still have a long way to go. Given the EPA range of atmospheric CO2 to lie between 535 and 983 by 2100, the resultant temperature increase lies in the range is 0.5 - 7.0 C (low-low to high-high). The pagani value was a calculated number for three different times in the recent geological past: 7.1 +/- 1.0, 8.7 +/- 1.3, and 9.6 +/- 1.4 C/doubling. http://earth.geology.yale.edu/~mp364/data/2009%20Pagani%20et%20al.pdf
  11. Jonathon, you appear to be missing the point. Nobody is claiming there is consensus on the exact value of climate sensitivity. There is however consensus on the range of values that would be plausible. If you want to claim that the scientists don't agree on the range of plausible values then please provide some evidence to support that assertion. Your comment on the Pagani estimate(s) still doesn't clarify whether it is a bound or an estimate of the most likely value.
  12. Jonathon, you're treating the extremes of the possible range as if they were equally probable as the mid range values. I doubt it is the case. The Pagani numbers should certainly give us cause for great concern.
  13. Jonathon - Looking at the Pagani paper, they are estimating equilibrium sensitivity, not transient sensitivity (the number usually listed as ~3°C/doubling of CO2.). Hansen estimated equilibrium sensitivity at ~6°C? So while the Pagani numbers are rather higher, they are really not directly relevant to the short term transient sensitivity of 3°C. Also, keep in mind that the high end of the sensitivity tail is much less determined than the low end. --- This is all smoke and mirrors on your part anyway, Jonathon. The consensus on values and ranges come from the evidence - if you wish to assert a climate sensitivity outside that range, present some evidence, not a petition.
  14. Dikran, I am not missing the point. I never said that there is a consensus on the exact value, so you can stop repeating yourself on this issue. I have yet to see anything that support a consensus on the range of plausible values, and highly doubt that one exists. Typically the evidence against a consensus is to present data which does not conform, which I have already done. The Pagani estimates are estimates of the value, not a bound. The uncertainties listed after each value are his calculated range. Clear? Philippe, When assembling a range of value such as this, each individual measurement is assigned the same probability, assuming they were determined independently, just like rolling the dice. If additional research yields values which begin to cluster around a specific range, then we can assign higher probability to those values. In the case of climate sensitivity, we see values clustered not around a mid-range value, but at the high and low ends, but still yielding a similar mid-range value. This anti-Gaussian distribution would indicate that the mid-range value is less likely than either end.
  15. Jonathon, I am curious. What is your reference for Hansen believing sensitivity to be 6? Wasnt what he said in public meeting I attended. Also, in consensus. Am I correct in assuming that in your mind, if there is a published value outside a consensus range, even in a refuted paper, then consensus doesn't exist?
  16. Continued sensitivity discussion is better suited to the existing sensitivity thread. The consensus there is 3.5 deg C per doubling.
  17. Scaddenp, (-Snip-). The Hansen value can be found here among other places: http://www.skepticalscience.com/Climate-emergency-time-to-slam-on-the-brakes.html Muon, We are discussing the range, not a value.
    Response:

    [DB] Inflammatory snipped.

  18. Jonathon, two very simple questions. If the range of plausible climate sensitivty values is 1.5C to 5C per doubling CO2, is there a consensus that the climate warms with added CO2? Yes or no? If the range of plausible values for the Hubble Constant is 55-80km/s/Mpc, is there a consensus that the Universe is expanding? Yes or no?
  19. Johathon, "climate sensitivity" = short-term transient sensitivity = fast feedbacks = 3 deg C The 6 deg C figure you keep providing is for long-term sensitivity / slow feedbacks.
  20. Sky, We already answered that on the other thread - yes. The discussion here is about whether we can say that there is a consensus among scientists as to the sensitivity of the temperature to CO2. We have already agreed that exact value in unknown, and that there is a plausible range of values. The disagreement is about what is that range, and is it narrow enough to constitute a consensus. Your range for the Hubble is much narrower, and not being a cosmologist, I cannot appropriately answer your question. Biblio, If we are talking about short-term transient sensitivity, then the plausible values are much lower, and Hansen's value of 3 is still on the high side. The following might help clear this up for you. http://profmandia.wordpress.com/2011/01/18/clearing-up-the-confusion-about-climate-sensitivity/ http://journals.ametsoc.org/doi/abs/10.1175/2011JCLI3989.1
  21. Jonathan wrote: "The disagreement is about what is that range," as far as I can see you have provided no evidence that there is substantial disagreement regarding the range of plausible values, just that there are point estimates that are not in close agreement.. "and is it narrow enough to constitute a consensus." The spread of the range of plausible values has no bearing whatsoever on whether there can be a concensus on what the range actually is. If we had some dimensionless quantity that physics constrained to be strictly positive, but otherwise we knew nothing about it, then it would be perfectly reasonable for the concensus to be that the plausible range were from 0 to +infinity.
  22. The article you posted states that the most likely climate sensitivity is 3 deg C. How is 3 on the high side of 3?
  23. Biblio. That is for equilibrium climate sensitivity. I though you were talking abobut transient sensitivity, which the first article states as 1-3, while the second says 1.3-2.6. In either case, 3 is on the high side for transient sensitivity. Please read more carefully.
  24. Bibliovermis, 3 is on the high side of 3, but only for large values of 3 ;o)
  25. Dikran, The argument that everyone is in agreement, because we all think that the value is positive, is nice, but does not tell us much. If that is the extent of the consensus, then we should just drop it altogether. Since no one wishes to go beyond that issue, there is really no point arguing any further.

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