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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 626 to 650 out of 906:

  1. Of course the framing document is not a position paper expressing skepticism on climate change. But they are serious questions that good scientists are asking. The IPCC report makes strong statements and the APS committee is inquiring into the basis of those statements. The 2007 APS statement on climate change is one of the pillars of the scientific consensus on climate change. That position is being reviewed by this committee. I think they are asking good questions. I would assume there are good answers and that is why I asked if they had been addressed. But so far I only hear defensive responses that don't address substance. If all you have is condescension, I am clearly in the wrong place for information.

  2. Well I havent read every line the workshop transcript but it certainly looked to me like the questions likely of interest to L,C&C were being addressed. Got an example of a particularly interesting question that you feel was not addressed?

  3. "How are IPCC confidence levels determined?"

    "What caused the 5% increase in confidence from 2007 to 2013?"

    How is the persistent factor of 3 uncertainty in climate sensitivity consistent with the IPCC confidence levels?

    How long must stasis exist before a firm declaration of a problem with the models?

    There also was a discussion (p 11) of the uncertainty of ocean heat flux data being 10-20% (or 20 W/m2) versus the change in global heat flux due to AGW since 1900 being less that 2 W/m2 (a factor of 10 less).

    I guess these would be a starting point....

  4. PhysicsProf @628:

    1) 

    "How are IPCC confidence levels determined?"

    As with many of the questions in the framing document, this question merely demonstrates the authors of the questions simply could not be bothered doing their homework:

    http://www.ipcc.ch/pdf/supporting-material/uncertainty-guidance-note.pdf

    2)

    "What caused the 5% increase in confidence from 2007 to 2013?" 

    There is a whole chapter of the latest IPCC report on this topic, which apparently the framers of the question could not bother to read.  Here is the summary:

    "Combination of Evidence
    Human influence has been detected in the major assessed components of the climate system. Taken together, the combined evidence increases the level of confidence in the attribution of observed climate change, and reduces the uncertainties associated with assessment based on a single climate variable. From this combined evidence it is virtually certain that human influence has warmed the global climate system. Anthropogenic influence has been identified in changes in temperature near the surface of the Earth, in the atmosphere and in the oceans, as well as changes in the cryosphere, the water cycle and some extremes. There is strong evidence that excludes solar forcing, volcanoes and internal variability as the strongest drivers of warming since 1950. {10.9.2, Table 10.1}"

    If that is not clear enough, let me spell it out.  The attribution is for anthropogenic warming since 1950, ie, 60 odd years ago.  The most commonly cited frequency for major oceanic fluctations is 60 years.  A 60 year cycle will not raise temperatures over a full cycle.  Therefore oceanic fluctuations are eliminated as a significant factor.  Net volcanic foring and solar forcing since 1950 have been negative, or nearly so.  Therefore they are not the cause of recent trends.  That leaves anthropogenic factors as the dominant (>50%) cause of the warming.  That conclusion is further supported by fingerprint arguments, and more detailed attribution in a host of areas.  The increase in confidence comes because, firstly, at time extends to 60 years the potential role of oceanic cycles minimizes; and as we continue through the very low activity of the current solar cycle, the potential that it was the Sun further minimizes.

    3)

    "There also was a discussion (p 11) of the uncertainty of ocean heat flux data being 10-20% (or 20 W/m2) versus the change in global heat flux due to AGW since 1900 being less that 2 W/m2 (a factor of 10 less)."

    From the relevant chapter of the IPCC:

    "3.4.2.3 Net Heat Flux and Ocean Heat Storage Constraints 

    The most reliable source of information for changes in the global mean net air–sea heat flux comes from the constraints provided by analyses of changes in ocean heat storage. The estimate of increase in global ocean heat content for 1971–2010 quantified in Box 3.1 corresponds to an increase in mean net heat flux from the atmosphere to the ocean of 0.55 W m–2. In contrast, closure of the global ocean mean net surface heat flux budget to within 20 W m–2 from observation based surface
    flux data sets has still not been reliably achieved (e.g., Trenberth et al., 2009). The increase in mean net air–sea heat flux is thus small compared to the uncertainties of the global mean. Large and Yeager (2012) examined global ocean average net heat flux variability using the CORE data set over 1984–2006 and concluded that natural variability, rather than long-term climate change, dominates heat flux changes
    over this relatively short, recent period. Since AR4, some studies have shown consistency in regional net heat flux variability at sub-basin scale since the 1980s, notably in the Tropical Indian Ocean (Yu et al., 2007) and North Pacific (Kawai et al., 2008). However, detection of a change in air–sea fluxes responsible for the long-term ocean warming remains beyond the ability of currently available surface flux data sets."

    First note that the increase in ocean heat content is tightly constrained.  As it happens the total Earth surface change in heat content from 1971-2010 was to 274 [196-374] zetajoules.  That equates to a forcing of 0.42 [0.3-0.54] W/m^2 averaged over that period.  93% of that warming was in the ocean.  Over that period, solar forcing was net negative, volcanic forcing was net negative, and oceanic fluctuations cannot give the ocean heat, merely shift it around.  That leads to the IPCC conclusion that it is "very likely" that anthropogenic factors have "made a substantial contribution to upper ocean warming" using a method independent of observation estimates of the value of individual fluxes.

    However, the IPCC quote properly refuses to specify the contribution form the magnitude of any individual flux, or combination thereof because the evidence on individual fluxes is not exact enough.  This, quite frankly is kindergarden stuff.  If we have a pool being filled from three different sources, each of which varies substantially from minute to minute in its outflow, but the volume of water in the pool increases steadilly, we know the net flow into the pool is positive and the average flow per minute even though we may be completely in the dark as to which source provides the greatest contribution in any given minute.

    4)  As shown above, the questions raised by you echoing the framing document have been more than adequately answered by the IPCC already.  It is sufficient response to all of them (and all the questions in the framing document I have read) to simply reply, read the IPCC report.  Of course, the original framers of the questions obviously have read sufficient of the report to present facts out of context, and frame questions in such a way as to create maximum confusion, even though a simple reading of the report already answers all the questions.

    I emphasise "original" because it is quite possible, indeed probable if they are competent, that the APS committee has just presented a document of denier talking points so that said deniers cannot reasonably complain their points have not been addressed. 

     

    PS: @623 you wrote ' "you're a denialist"--because Holocaust imagery is always in good taste" '.  Everybody else will have noted that you are the only person invoking the Holocaust here.  The will probably recognize that if you call Paul tall, that does not prevent you calling Mary tall as well, and that in no way implies they have the same gender.  Likewise, if some people have called people who doubt the history of the Holocaust on unreasonable grounds "Holocaust deniers", that I call people who doubt AGW on unreasonable grounds "AGW deniers" in no way implies that the latter have offensive views on the Holocaust - only that they deny AGW on unreasonable grounds.  My language is not limited by your determination to use the taking of  offense as a rhetorical tactic.

    PPS:  This is all well of topic on this thread, and I expect any reply on any of these issues (or other questions) to be in an appropriat thread.  Not doing so is a vioation of the comments policy and should result in your comment being summarilly deleted.

  5. I guess one could stretch the argument that, if APS revises isstatement, the consensus amongst scientists (not clkimate scientists) could be weakened and perhaps that's why PhysicsProf brought it up here. I am still unimpressed by the contents of that "framing document." I disagree that it resembles scientists asking questions in a sincere effort to understand. The arguments in it are well examined in the IPCC report. All of them are the object of current research and an abundance of litterature exists on them. Quite frankly, it reads more like a gish gallop and does not carry the to me the impression of sincerity that PhysicsProf advertises. I do not find that expressing this constitutes condescension.

  6. From what I gathered from people who were at that workshop, the APS board had a clear understanding of the situation ahead of time. It sounded like this was more about giving certain "skeptics" a chance to vent ahead of updating the APS position statement. 

    I would guess the framing document was a way of pulling up questions that "skeptics" put forth, though knowing those questions have been already answered to full satisfaction by the IPCC.

    I agree with Philippe. This doesn't strike me as a reasonable list of questions, except to those who don't have a full grasp of the scientific evidence on climate change. It's a list of talking points that have been addressed, repeatedly, in full.

  7. Well the questions Physicsprof thought interesting would mostly be case of RTFM, so no surprize that not much discussion of them. LC&C are very familiar with the content of the IPCC WG1. What is more surprizing is why these questions were there at all. It does not seem reasonable to me that anyone in APS who is questioning the consensus on climate change would not have read the document.

  8. Given an organism in an environment one can state that the most adaptive will, by definition, be the most likely to survive. In order to adapt to an environment, an organism must understand it. One could say that the ability to understand ones environment is perhaps the best measure of intelligence that exists. As far as evolution is concerned it is the only measure that counts. Being able to do math and calculate a trajectory does not count, but being able to dodge a predator definitely does count. If two organisms share about the same abilities to react to a given situation then the organism that can read the situation the most accurately is the one most likely to survive.

    Now consider Global warming. A search of the internet will quickly demonstrate that the vast majority of species on the planet are moving to the poles, or are moving, if they can, to higher elevations. In addition to that, the timing of migration patterns are changing. If this data is not accurate then not only are all climate scientists part of this climate gate conspiracy, but so are all botanists, ethologists, marine biologists, and microbiologists, entomologists and probably some others. So there is the first bit of information: If you do not believe that the climate is warming on a global scale then in terms of evolution you are less knowledgeable about your environment (less intelligent) then the great majority of animals, plants, insects, and even ocean dwelling single celled organisms like plankton. Yep, you are dumber than a plant or an insect.
    http://news.discovery.com/earth/global-warming/animals-migrating-north-global-warming-110818.htm

    The pattern of GW denial sort of follows that of, and is similar to the arguments used to deny the correlation between smoking and cancer and a host of other diseases. You had actual scientists looking at the best available evidence on one side, and then you had paid charlatans with degrees in science working for corporations whose interests were threatened on the other. That was not 100% mind you, but it was pretty much how the advocates of the two positions lined up. A prime example is Dr. Frederick Seitz who sold out to become a spokesman for big tobacco and tried to convince people that tobacco was harmless. Later, after, at least according to many who were close to him, he became senile, he sold out to climate deniers.

    Now in this case on one side we have not only actual scientists doing their best to explain available information in light of best understood implications of thermodynamics, quantum mechanics, black body radiation etc. but you have almost all other life forms on the planet. By other forms of life, I mean almost every entity on the planet living in all but the most except extreme areas.

    Now if we accept GW, the next question is: what causes it? Trust me, it is not the sun which for the past 50 years has remained fairly constant or produced less radiation over that time while temperatures have risen. It has not changed much in the past 2000 years. Neither has known cosmic ray counts. This leaves galactic unicorn farts and CO2. We know about CO2, and how it would work, and the most likely results. We have no evidence of unicorn farts, but we do know about bloviation sources from hot air producers.

    Another red herring from AGW people are the failure of computer models and the testability of theories. If the prediction of a theory fails then the theory is false. Well folks, then I guess that the germ theory of disease is false. Clearly, many people exposed to "so called germs" never get sick. On the other hand people get sick who have never been exposed to these "so called germs" But wait, they are not really germs, they are viruses. See -— those scientists keep changing their story. Because they are in the pay of big pharma who just want to sell us drugs to make us sick so that they can make us more sick. And space that is another hoax. You know that the sun goes around the earth, just go outside and look for yourself. What? You believe the so called scientists?

    And speaking of hot air producers. This is a standard equation in statistics, the Gaussian integral. http://en.wikipedia.org/wiki/Gaussian_integral. If you can not follow the proof, then you do not have a basic understanding of one of the most basic equations in statistics, which means that you do not understand statistics, which means that you are as competent to argue a point of view on AGW as you are to advocate competing forms of cancer treatment without ever having had a course in biology.

    But since AGW deniers acutely suffer from Dunning-Kruger effect: http://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect, they will continue to bloviate.

  9. Link is broken:

    13 countries have signed a joint statement endorsing the consensus position: 

  10. If we acknowledge that 97% of climatologists agree with the concept of anthropogenic global warming can we a) agree that 97% is less than 100%, and b) that scientists have, throughout history, repeatedly come to majority conclusions that were wrong, and therefore c) admit that consensus on issues of scientific inquiry conveys no moral or intellectual prerogative?

  11. Andy Robinson - We can certainly agree on that, as well as noting that

    • d) Usually the majority of experts are indeed correct, and
    • e) Holding minority positions (far less than 1% per hypothesis, as there are multiple and contradictory proposed 'climate skeptic' mechanisms) means holding to a position that most people familiar with the subject(s) feel is in no way credible. 
    • f) For people not deeply versed in a complex subject, expert opinion makes for the most reasonable heuristic in deciding policy - to do otherwise is a very bad, and in fact irrational, bet.

    To act as if the minority opinions are in fact correct is to fall prey to the Galileo fallacy - if people perceive you to be wrong, you usually are wrong. There are far far more loons doing living room 'science' than actual geniuses out there. 

  12. KR @636

    We can also note that even when scientists are wrong, they are often right enough (e.g. Newton's laws of motion)

  13. If the question in the concensus sudy had been "Is recent climate warming solely due to human influences" then it would be interesting to know what the answers would have been.

    Of course concensus doesn't mean right which is the implication of the video. Concensus is always being proved wrong and science doesn't work and never has worked on the basis of concensus as I hope all the participants on this site well know.

    Thirty years ago there was an unshakeable concensus in medical science that the main group of stomach ulcers were caused by excess acid secretion. It took a new scientific discovery to prove that the concensus was wrong. The cause of an unpleasant condition that had affected more than 1 billion people and that affects around half the US population over 60 years old is a bacteria Heliobacter Pylori. New drugs were invented that treated it and the previous treatment was dropped.

    Of course it is worth knowing that 97% of research papers and / or their authors attribute global warming to humans but as the video says, it's the science behind it that counts, and just because the papers are peer reviewed in itself proves nothing about whether the scientific proposal / theory is necessarily right. Some ability to falsify the theory must exist (as happened in the case of H.pylori) otherwise it's just the latest best estimate - no matter how great the concensus.

    The fact that only half the public believes that it is proven that AGW is the sole or main cause of global warming says something to the idea that the proof is not necessarily there and publicising it (there has been a ton of that) can't alter the impression that there is a long way to go before we are remotely close to knowing for certain. 

    One reason for being confident about there being much more uncertaintly than the 97% concensus suggests is that there is nothing like a concensus, let alone proof, of what caused (and causes) the extreme natural variations in climate throughout geological time.This variation is well documented and almost certainly has a variety of underlying causes which are likely to be very different from C02 or other MM emissions even if higher greenhouse gases levels have often been present. For example we do know that glaciers existed at the poles when C02 levels were a hundred times the current concentrations. 

  14. Peter Lloyd @638...

    My first question for you would be: Have you read the Cook et al paper yet? I ask this because you seem to be operating under a number of assumptions that in error.

    Firstly, the basis of the study was to evaluate whether research papers endorsed or rejected the IPCC position that human's are primarily responsible for warming of the past 50 years. The IPCC statement on this matter suggest that there is a >95% confidence level that human's are responsible for more than half of the warming. Part of the position the IPCC states is tha the most likely figure is that human's are responsible for 110% with a high end likelihood of 160%.

    Even at >100% contribution no one is going to claim that human's are "solely" responsible for warming. There are always natural warming and cooling factors at work. Thus, your statement would be one that 100% of scientific researchers, and scientific research would reject.

    Secondly, you appear to be under the incorrect assumption that Cook et al was attempting to infer whether the science was "correct." That is not the case. If you read the paper, the whole point is that most non-scientists do not understand what the actual level of scientific consensus is. The paper is quantifying the consensus and presenting that in juxaposition to what the general population thinks the consensus is.

  15. "Concensus is always being proved wrong and science doesn't work and never has worked on the basis of concensus as I hope all the participants on this site well know."

    This argument makes no sense.  There is now a consensus that H. pylori is important in most ulcer cases. Your argument suggests should we ignore that consensus because it could be wrong.  But that is the case with any proposition open to scientific questioning.  

    You are getting "faith" mixed up with "consensus."  Consensus is about the current state of understanding given the information in front of us.  It is critical to progress in science since it provides the methods, assumptions and questions needed to direct futher study.  Without consensus, science would slow to a stand still because there would be no agreement about assumed knowledge to direct future research.  In the case of H pylori, the question now becomes why 2/3s of people are infected, but relative few show any syptoms.

    What consensus is not is unshakeable belief in a proposition. Consensus can be overturned because it is based on evidence.  If evidence suggests the consensus should be overturned, a new consensus usually forms around a new proposition that is better supported by the evidence.  Such paradigm shifts are extremely important in science, and come in all shapes and sizes.  Much research can be seen as interesting because it challenges assumptions.  But large scale revolutions, where a well established point of consensus that is central to many lines of research is overturned in favor of a new idea, is not the rule.  That is why Kuhn referred to normal science in opposition to revolutionary science.

    Climate science has settled on a consensus about current warming because the evidence points in a particular direction.  At present there is no alternative hypothesis that fits the observations in front of us.  Could there be an H. pylori we haven't seen in the climate that causes recent warming?  Given that climate is governed by well established (by consensus) laws on transfer and conservation of energy, and we can measure most of the key flows and modifying factors, it seems unlikely. You would have to challenge the consensus on thermodynamics, or radiative transfer, or physical chemistry, because those agreed principles underlie this more specific consensus.

  16. The consensus on stomach ulsers story you present is one that has little basis in fact. Here is what Dr Marshall said of their work:

    Even after your self-experiment, the medical community remained sceptical that H. pylori was connected to stomach ulcers. How did you finally convince them?

    We were keen to present our data and announce that we had discovered the cause of ulcers, so we submitted our paper to the Australian Gastroenterology meeting in 1983. It was rejected. Fortunately, my boss at the time had some experience with Campylobacter, which was becoming a popular explanation for infectious colitis, or inflammation of the colon. Helicobacter looked similar, so I spoke to a Campylobacter expert in Britain and we sent him some cultures. He grew them and became excited about it, too. Then, in 1984, we went to a meeting of microbiologists, who are always interested in any new microbe, and things really took off after that. It took a few more years to gain support from gastroenterologists.

    [added emphasis]

    As you can see, this was an idea that did not take long for the scientific community to accept.

  17. In short, the consensus is not about blind acceptance.  The consensus has power precisely because scientists are challenging or have continually challenged it in various ways, and yet it has stood. The idea that there is a dichotomy between consensus and skeptical inquiry fails to appreciate how the process works..

  18. Thank you gents

    I haven't had a chance to read the paper and accept the point about endorsement of the IPCC position

    Thank you for agreeing that there are other factors at work in global warming and bearing in mind the strength of those as demonstrated by climate history then any claim that man - made factors are anywhere near as large as 100% or greater are going to have to demonstrate the current and past natural changes and how they interact. No one knows this yet.

    I would point out that the huge red circle at the top of this thread with the 97% figure in it says "Global warming is happening and we are the cause" without the caveat that it is not the only cause.

    As a result, however interesting it may be that half the population doesn't share the 97% figure, the concensus view remains guesswork and miles away from the experimentally demonstrated effect of H. pylori that I used as a contrast.

    You don't show in what way my H. plyori story has "little basis in fact" or isn't relevant. It is true that H.pylori is the primary cause of many stomach ulcers. There undoubtedly will be many elements of how and why that remain unknown as yet. The point is not to make too much of the fact that there was a strong concensus about the previous view. In general medical science is quite good about not creating an idea of certainty unless the experimental evidence is very strong indeed.

    My problem with the waving around of the 97% figure is it gives a false impression of the certainty if you don't temper it in the same pronouncement. 

  19. Peter Lloyd:

    You are essentially admitting to arguing from ignorance. Please desist (arguing from ignorance, that is).

    Maybe you don't know much about paleoclimate, but that doesn't mean nobody knows. (See chapter 5 of the IPCC AR5 WG1, or any paleoclimate articles at this website.)

    Maybe you don't know much about the sum of radiative forcings, or findings from paleoclimate, that allow climatologists to calculate that human emissions of greenhouse gases are responsible for 100+% of recent warming, but that doesn't mean nobody does.

    Regarding paleoclimate findings supporting "global warming is happening and we are the cause", see Tom Curtis' comment here regarding Marcott et al 2013; in which Tom notes that Marcott et al found:

    Global temperature, therefore, has risen from near the coldest to the warmest levels of the Holocene within the past century, reversing the long-term cooling trend that began ~5000 yr B.P.

    In other words, little temperature wiggles up-and-down notwithstanding, human emissions are the only cause of the current sustained warming trend.

    Maybe you don't know about the enormous evidence base that undergirds the consensus position, but that doesn't mean nobody does - in fact, the consensus position exists as a result of the evidence base (Like in any other field of science with a strong consensus position (*)).

    As just a tiny example, consider this Skeptical Science post discussing the basics of the greenhouse effect. Note the final image presented in the article, taken from Conrath et al 1970 in which they ran an experiment, comparing theoretically calculated vs. empirically measured infrared radiance.

    Kindly also provide actual documentation that the mainstream position among doctors and medical researchers regarding stomach ulcers was an "unshakeable consensus" as you assert.

    (*) Unless you care to suggest that, say, plate tectonics, quantum electrodynamics, gravity-as-distortion-of-spacetime, and evolution of biological organisms are also "guesswork".

  20. Peter Lloyd...  "You don't show in what way my H. plyori story has "little basis in fact" or isn't relevant."

    You stated that there was an unshakable consensus. I quoted for you the words of one of the researchers who discovered the H. plyori saying it only took a few years for his work to become accepted. That means, in actuality, that previous consensus was very quickly overturned by presenting the research.

  21. 645. I think we are at cross purposes here. Neither of us doubt that there was a, let's call it strong, or established if you like, consensus prior to the discovery of the effect of H. pylori. Neither of us disagrees that new evidence did change the consensus although I would argue that the fact that it took as long as it did illustrates that medics were very keen to hold on to their previous consensus view.

    Where we would probably disagree is on whether there is sufficient scientific proof underlying the consensus on the degree of man-made global warming and the degree to which that consensus is reflected correctly in the statements made at the top of this thread.

    I think that looking at the science and its credibility is important and that the use of "consensus" is being corrupted to give a false impression of certainty

    644. No. I am arguing that there is ignorance and you seem to be in denial of it! It is freely admitted by paleo-climatologists that they know a lot about many of the factors involved but not enough to know the exact reasons behind paleo-climatic changes. 

    Taking your Tom Curtis conclusion from Marcot et al:

    "Global temperature, therefore, has risen from near the coldest to the warmest levels of the Holocene within the past century, reversing the long-term cooling trend that began ~5000 yr B.P.

    and your conclusion from it:

    "In other words, little temperature wiggles up-and-down notwithstanding, human emissions are the only cause of the current sustained warming trend."

    The conclusion you draw cannot logically be made from that Marcot statement. There maybe many reasons for the cooling and for the most recent warming of which human emissions are likely to be a contributory factor. 

    The enormous evidence base that you cite does not preclude other factors causing the most recent warming and whilst you are right that there is a lot of knowledge about paleo climate I have yet to see anything that comes close to proof that C02 changes are the main factor in those. As I said before icecaps existed at both poles when C02 concentrations were 100 times the current levels.  

    ...."Unless you care to suggest that, say, plate tectonics, quantum electrodynamics, gravity-as-distortion-of-spacetime, and evolution of biological organisms are also "guesswork"."....

    I don't care to say it because they are all demonstrably true and repeatedly proven by observation and / or experiment. The theories and mechanics behind them have been, and are, still subject to many different "consensuses". But none of those causal theories are held as unshakeable truth in the way, say for example, that the movement of crustal plates is, via something described as plate tectonics. This will not be falsified.

    The same cannot be said for the claim that man-made emmissions of C02 are causing 100% (ish) of temperature increases on earth.

    Response:

    [JH] You are now skating on the thin ice of excessive repetition which is banned by the SkS Comments Policy.

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

  22. Peter... The point isn't that it took so long. Once actual evidence was presented scientists changed their position based on the evidence. The previous position was one where there was little active research that made up the basis of the consensus position. 

    AGW is not a case where little research is being done and scientists are just accepting what has been assumed.

    This is an issue that has been actively researched for 100 years. There are thousands of papers coming out every year on various aspects of man-made climate change. It's a field of intensive research.

    In the past 100 years there have been various challenges to the core idea that increasing greenhouse gas concentrations will warm the planet. Each of those challenges have been shown to be wrong. And in the meatime, more and more research is being published confirming the consensus position.

    The comparison to H. pylori is just not a valid.

  23. Peter Lloyd - The consensus on AGW, although very consistently measured in the high 90%'s, is not immutable

    In the early 20th century the consensus on climate was that natural causes predominated. There were early researchers like Tyndall Fourier, and Arhennius who made some quite prescient predictions, but until the mid-20th century there was no general opinion that anthropogenic factors were important. But then things changed due to new evidence. Callendar in the 1930's (AGW a factor in early 20th warming), Plass (radiation balance) and Revelle (oceans won't absorb all anthropogenic CO2) in the 1950's, Keeling measuring CO2 in the 1960's, Manabe and others in the 1970's modelling GHG effects, etc - all contributed to the body of evidence. 

    And over the 1960's-1980's, the scientific consensus on climate changed, to the currently held view that AGW is the dominant factor in recent warming, accounting for ~100% of it (with natural factors such as insolation providing negative contributions)

    The consensus changed due to evidence and how it is viewed by those who have studied these topics. It could certainly change again - but that would require a considerable amount of new (and contrary) evidence to that effect. There's no sign of such whatsoever - just inconsistent, contradictory and unsupported claims (it's the sun, it's a cycle, cosmic rays, it's not happening at all, there's a grand conspiracy toward a 'World Order', etc), claims that appear, quite frankly, loony. 

    Now, as to the meaning of such a strong scientific consensus - that's important because laypeople (quite wisely) will take expert opinions into consideration when deciding public policy. 

    You've claimed uncertainty where it doesn't exist. And your comments simply don't hold up in the face of the evidence. 

  24. "The enormous evidence base that you cite does not preclude other factors causing the most recent warming."

    Actually, it does preclude them as that list is really rather small.  It would have to be something that affected the net heat balance of the earth by affecting incoming radiation (solar inputs, aerosols, clouds), the reflectivity of the earth (ice caps, land use changes) or the ability of the surface to cool (greenhouse gases).  The only thing that has been changing in a way that should increase global heat balance over the last 40 years are greenhouse gases.  

    Your equivalent of H pylori would be to discover a new way for heat to be produced, absorbed or lost by the atmosphere in a large enough quantity to challenge the importance of those other factors.  I'd argue the likelihood that such a missing component of the heat budget exists and has not been seen is virtually nil, because we can close the heat budget now.

    "and whilst you are right that there is a lot of knowledge about paleo climate I have yet to see anything that comes close to proof that C02 changes are the main factor in those. "

    First, what explains variations in paleo climate does not have to be the same thing that explains current climate change.  I.e., The glaciations were not initiated by CO2, but they were exacerbated by feedbacks that increased CO2.  Current warming is only really related to changes in greenhouse gases though.

    Second, we will always know less about what drives paleo climate because we know less about the key factors that drive global heat balance in the distant past than we know about the present, for which we have precise measurements.   The lack of certainty about past climate variations does not undercut what we have learned by studying current conditions.  Still, there have been puzzles raised by past climate conditions that have seemed to challange the consensus, which has generated futher research to understand the factors underlying the energy budget better for those periods.  I can't think of a current case in paleoclimate, however,  that hasn't been reconciled with the accepted role of CO2 in climate once more was understood about conditions affecting the earth's energy balance.

    "As I said before icecaps existed at both poles when C02 concentrations were 100 times the current levels."

    A case in point.  Actually, the high CO2 concentrations during large glaciations in the paleozoic were discovered by scientists trying to understand how the earth became deglaciated after essentially freezing over.  Glaciation of the earth should have been hard to overcome because a white earth reflects a lot of sunlight, and therefore greatly reduced incoming energy. That lead many to doubt evidence that the earth was actually glaciated — because it still would be.  

    But, the glaciations alsostopped processes that typically removed CO2 from the atmosphere, allowing it to build up, which heated the earth and allowed the glaciers to melt.  So paradoxically, the phenomenon you hold up as challenging a role for CO2 in climate, is actually understood by scientists to reinforce the idea that CO2 is important in climate.  

    Response:

    [PS] See here and here and here for the science on climate and past high CO2 levels. One of the most popular myths.

  25. This story

    LINK

    came up yesterday, about the consensus; I wonder if it deserves a response?

    Response:

    [RH] Hotlinked url.

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