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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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Is the science settled?

What the science says...

Select a level... Basic Intermediate

That human CO2 is causing global warming is known with high certainty & confirmed by observations.

Climate Myth...

The science isn't settled

"Many people think the science of climate change is settled. It isn't. And the issue is not whether there has been an overall warming during the past century. There has, although it was not uniform and none was observed during the past decade. The geologic record provides us with abundant evidence for such perpetual natural climate variability, from icecaps reaching almost to the equator to none at all, even at the poles.

The climate debate is, in reality, about a 1.6 watts per square metre or 0.5 per cent discrepancy in the poorly known planetary energy balance." (Jan Veizer)

Skeptics often claim that the science of anthropogenic global warming (AGW) is not “settled”. But to the extent that this statement is true it is trivial, and to the extent that it is important it is false. No science is ever “settled”; science deals in probabilities, not certainties. When the probability of something approaches 100%, then we can regard the science, colloquially, as “settled”.

The skeptics say that results must be double-checked and uncertainties must be narrowed before any action should be taken. This sounds reasonable enough – but by the time scientific results are offered up to policymakers, they have already been checked and double-checked and quintuple-checked.

Scientists have been predicting AGW, with increasing confidence, for decades (indeed, the idea was first proposed in 1896). By the 1970s, the scientific community were becoming concerned that human activity was changing the climate, but were divided on whether this would cause a net warming or cooling. As science learned more about the climate system, a consensus gradually emerged. Many different lines of inquiry all converged on the IPCC’s 2007 conclusion that it is more than 90% certain that anthropogenic greenhouse gases are causing most of the observed global warming.

Some aspects of the science of AGW are known with near 100% certainty. The greenhouse effect itself is as established a phenomenon as any: it was discovered in the 1820s and the basic physics was essentially understood by the 1950s. There is no reasonable doubt that the global climate is warming. And there is also a clear trail of evidence leading to the conclusion that it’s caused by our greenhouse gas emissions. Some aspects are less certain; for example, the net effect of aerosol pollution is known to be negative, but the exact value needs to be better constrained.

What about the remaining uncertainties? Shouldn’t we wait for 100% certainty before taking action? Outside of logic and mathematics, we do not live in a world of certainties. Science comes to tentative conclusions based on the balance of evidence. The more independent lines of evidence are found to support a scientific theory, the closer it is likely to be to the truth. Just because some details are still not well understood should not cast into doubt our understanding of the big picture: humans are causing global warming.

In most aspects of our lives, we think it rational to make decisions based on incomplete information. We will take out insurance when there is even a slight probability that we will need it. Why should our planet’s climate be any different?

Basic rebuttal written by James Wight

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Last updated on 7 July 2015 by James Wight. View Archives

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Comments 26 to 50 out of 81:

  1. Eric, it's frustrating that you merely repeat your assertion without responding to the evidence I have provided in links. Here is another link, this one about underdetermination of scientific theory, from the Stanford Encyclopedia of Philosophy.
  2. Tom, thank you for that latest link which I have saved and will reread on occasion. Unfortunately I can't respond on this topic anymore.
  3. But Eric, why do all scientists in all disciplines use the phrase "competing theories," since by your definitions such things cannot exist? According to you, in each domain there can be only "the" theory in which 100% of scientists have 100% certainty, plus competing "notions." So you call string theorists mere "string notionists"? But if 100% of scientists are 100% certain about the non-string physics theories, then those string notionists are not really scientists at all! They are poseurs! Another implication of your claims is that inferential statistics must never be used to analyze data, if those data are going to be used to verify a theory, since you claim that evidence less than 100% certain cannot be used to support a scientific theory, and inferential statistics yields probabilities between 0 and 1, exclusive. You also drastically restrict the ways in which a theory is replaced. If 100% of scientists are 100% certain in the correctness of "the" theory, then none of them would waste their time even entertaining alternate notions, let alone actively constructing alternate notions nor collecting data to support alternate notions. Nor would they waste their time gathering more evidence in attempts to further support the existing theory. The discovery of data that the current theory cannot handle must happen only accidentally, then. Clearly that is not how science really works. And then there is the problem of incomplete theories. Classical, Newtonian, theories of physics cannot explain the things that relativity theory and quantum theory can explain, and the latter two cannot explain everything, either. So by your definitions, none of those is a theory; all are mere notions. Which means there are no theories of physics right now!
  4. Tom, I had to break my rule after adding "empirical" to your google search for "string theory". In the first link returned the author might suggest that I am a logical positivist, stuck in the early 1900's. The author says "Einstein, Dirac and many other scientists had intuitive kind of faith in the correctness of their theories without empirical evidence." He goes on to say they used subjective criteria to underlie that faith. I have that same faith in my theories of the world except I am not capable of venturing into relativity except where it is actually empirical. Given new evidence or new theories that conflict with mine, I will change to the combination of old and new theories that are completely consistent with the evidence. As for (objectively) statistical evidence, I am probably guilty of what Hoekstra calls "probability as certainty" or "binary thinking". I take the view that most of those cases are avoidable, that direct evidence is available. While you again appeal to the concept of "theory-laden" observations, I reject the idea that good scientists would not look for counter-evidence that is not biased or tainted by their current theories. I think we will have to agree to disagree on that.
  5. Eric #29: I reject the idea that good scientists would not look for counter-evidence that is not biased or tainted by their current theories Einstein: Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the "old one." I, at any rate, am convinced that He does not throw dice. Me: So Einstein questioned Quantum Mechanics by appealing to philosophy, an "inner voice" or religon, but not to any counter-evidence. Given that scientists are human beings, have belief systems and make their names by publishing it seems unlikely that any of them, which ever side of the debate they are on, would be completely unbiased, if only subconciously. What we should insist on is that the science as a whole be unbiased, not the individuals practising it.
  6. Eric, if as you wrote you chose to be 100% certain in your belief in a combination of classical, relativistic, and quantum theories that taken together are "completely consistent with the evidence," then you are being certain about at least one proven incorrect theory! Classical mechanics is incorrect if you observe with enough precision. It is not 100% correct for any cases, so you cannot restrict your application of it to certain cases just so you can have it be 100% correct. By your definitions, classical mechanics therefore is not a "theory" at all; it is merely a "notion." So you must believe that all scientists who use the term "classical mechanics theory" are wrong. Which leaves you alone being right. Which should give you pause. That was the reason I brought up the phrase "competing theories." Every scientist in every field uses that phrase, so are they all wrong and you are right? That was the reason I brought up "string theory." You can tack on the word "empirical" if you want, but that does not change my point that there is, to say the least, inadequate evidence to make most scientists 100% certain that string theory is 100% correct and non-string theories incorrect. Yet scientists use the term "string theory" instead of "string notion." Are they all wrong? Even worse for your position is the existence of multiple string "theories"--string theories competing among themselves! Yet scientists call all of them "theories." The reason I brought up inferential statistics as evidence for deciding if a theory is "correct," is that inferential statistics is all about certainty less than 100%. Yet inferential statistical results with certainties less than 100% are used in all scientific fields as evidence for theories. The relevance of all this to your original claim, and to the original post at the top of this page, is that climatologists are not cheating or being lax by stating subjective probabilities of theories being correct. That's how all real, working scientists in all fields work, even when they don't express those probabilities as numbers. Either all of them are wrong, or you are.
  7. Tom, classical mechanics is 100% certain within a frame of reference in which the evidence (measurements) are 100% consistent with the theory. As string theory evolves along with empirical measurement techniques, it will be validated or invalidated, e.g. Theories that are yet to be grounded or validated in any way are notions, but string theory is grounded since it already reconciles quantum mechanics and relativity. It lacks sufficient technology to be validated by a high energy particle predicted by the theory. Obviously such an area, far outside my expertise and classical intuition, is easy prey for a falsely subjective interpretation. As BP points out in another thread, the theory or hypothesis is correct or not and statistics are suitable for noisy measurements. There is no such thing as a noisy theory, noisy conceptual framework or noisy science.
  8. Eric - there is a relevant discussion on another thread, starting here (claim of certainty) and here (thoughts on induction in science).
  9. apiratelooksat50 - Karl Popper's works have very little to directly do with the topic of CO2 lag. On the other hand, you appear to have raised the question of whether the science is settled. Let's look at the science. The planet is warming - Temperature records - Sea level rise - Arctic melting - Antarctic melting - Glacial retreat, Greenland melting - Crops and plants flowering earlier Hmm, plenty of evidence there. CO2 is causing the warming - Other forcings don't match recent warming - CO2 has enough of an effect, also here - Other causes can't explain it Looks like CO2. We're causing it - Isotopic evidence - Carbon cycle and emissions - Multiple lines of evidence What we have, apiratelooksat50, is multiple lines of evidence pointing in the same direction - towards human driven global warming. The only real uncertainties at this point are in regards to climate sensitivity - how much the temperature will go up based on our CO2 inputs. Our data indicates a minimum sensitivity to doubling CO2 of about 2.5°C (quite certain), with an upper limit of 4-5°C (nowhere near as certain, might be higher). Now, if you want to discuss uncertainty, I would recommend looking at the various, contradictory skeptical arguments. Hypotheses without evidence, or worse yet evidence contradicting them. Hypotheses that do not explain what we see. Those are uncertain.
  10. KR, Thanks for the links. It will take me a while to check them out. Just being curious and not accusatory, do you and/or the other posters here look at other sites that are not pro-AGW? Pirate
  11. Re: apiratelooksat50 (35) Hmm, good question (no one's ever asked me that). I try to keep up on the literature itself as it comes out while reading older stuff I missed earlier as I find the time. That means reading a lot of stuff from NATURE, AGU, PNAS, GRL, AMS (I'm sure I'm forgetting some of the biggies; that's what links are for). Full studies I have access to or can find a free PDF of somewhere (Google Scholar is your friend in this regard). Abstracts and review articles also. Science sites. As for blogs, I pretty much limit myself to the science-based ones that have proven themselves over time (RC, Open Mind, Skeptical Science, Science of Doom, Chris Colosse's place, Neven's Sea Ice blog, etc). I frequent ScienceDaily and ReportingClimateScience for hints to advance notice of breaking papers. To boil that down: Peer-reviewed articles are the core. Augmented by commentaries in both scientific venues and scientific sites & blogs proven trustworthy. And then distill it down to this: Is it credible? Does it agree with what we have established as foundational? Why or why not? If not, what significance does that have (if any)? If it seeks to overturn established tenets, then exceptional claims require an even greater level of exceptional evidence. Etc. We were all given a mind. Some choose to use it for thinking. Some let others do the thinking for them. Our choice. (Apologies to any here whose site I didn't specifically name; I blame senescence) Oh, I listen to Buffett (and pretty much everything from 1960-2000 or so). And I'm pretty conservative. The Yooper
  12. @apiratelooksat50: "Just being curious and not accusatory, do you and/or the other posters here look at other sites that are not pro-AGW? " You seem to be under the impression that this site is "pro-AGW". It isn't. It is pro-science. This isn't an debate of ideas, or of opinion. It is a scientific debate. Sites that have an obvious political agenda (such as WUWT) are not science sites. Your comment about "libs" in a different thread belies your political views. You should really stop looking at the science through a partisan lens.
  13. @aspiratelooksat50 - 'pro' means 'for', 'anti' means 'against'. I don't know of anyone who is 'pro-AGW', although I have read facetious comments, mostly on denier sites, saying 'warming will be good'. I don't imagine any thinking person wants earth to be hotter than it's ever been since humans evolved.
  14. I am not particularly interested in what the uninformed, incapable think and especially not interested in politically-motivated deception. That said, I figure that I would hear of any significant papers that challenge the consensus from Roy Spencer, and also take note of opinions of Peikle Snr (not Jr) though its debatable whether you would call him a skeptic. Lucia's "The Blackboard" is interesting also. You can safely assume commentary that is based on papers that are not published (or published in E&E) then I am not going to take much notice of.
  15. Continuing with reply to comment #28 here. "... Climate Changes Scientists, and by implication all scientists, have failed to be truly open with the general public and recent controversies in science have harmed a lot of scientific arguments." All I saw was the YouTube clip of Nurse's program, but I got a distinctly different impression. The clip focused on the NAS letter regarding political attacks on science (climate science in particular), reprinted here: We are deeply disturbed by the recent escalation of political assaults on scientists in general and on climate scientists in particular. ... When someone says that society should wait until scientists are absolutely certain before taking any action, it is the same as saying society should never take action. ... Many recent assaults on climate science and, more disturbingly, on climate scientists by climate change deniers are typically driven by special interests or dogma, not by an honest effort to provide an alternative theory that credibly satisfies the evidence. So your notion that greater 'scientific openness' will restore public confidence is idealistic and unrealistic. Until the denier side steps up to the scientific bar and stands a round, it's a one-sided contest.
  16. MuonCounter, your cherry picking from a few minutes of a 57 minute long program. Hardly scientific. Lets be honest here, some of the worst attacks on scientists have been those who have raised genuine and scientifically researched objections to AGW precepts. They are automatically labelled "deniers" and there have been instances of jobs threatened, papers refused to be published, careers damaged and even threats against the person. This has happened in several areas of science, and I understand some advocates of AGW have also undergone similar attacks, this is and always must be wholly unacceptable. If you watch the entire episode, it should be on BBC iPlayer soon if not already, you will see that Paul Nurse presents a very balanced and unbiased view, bearing in mind he is a staunch advocate of AGW. The person who comes out looking bad is actually Phil Jones. Not only does he admit unprofessional behaviour by stitching together different data sets, he admits to ignoring FOI's and even requests from other researchers for his data models and sets. I do not believe he intended to mislead, he presented data in what he thought was an acceptable form for the audience it was intended. However he was wrong, but he should not be harried for that, he should be harried for lieing about it, then refusing FOI requests on information paid for by the British Tax Payers. He should be sacked from his position for this and this alone in my honest opinion. It was unprofessional, unacceptable and implies a degree of dishonesty. He has still not honoured those requests and has still failed to provide a lot of evidence that has been requested of him. However, this is drifting off topic. Paul Nurse presented a reasonably balanced argument in what was a limited time slot, he demolished a two faced dog (Journalist) with simple logical argument...which was a pleasure to see..and overall I think the program got across the message it was attempting to send..Science needs to be even more open and transparent than it has been because the world has changed and continues to change and scientists are not great "joe public" speakers or at dealing with the media in general.
  17. LandyJim, I think you saw what you wanted to see in that programme because Phil Jones came out of it very well - as a scientist trying to do his job, while trying to fend off spurious FOI requests. He explained very well what the splicing was all about and it was made clear in the programme that what he and his team at CRU had done, had been cleared by four enquiries. There was, of course, mention made of clearer explanations and the work and data being made more available, but the programme certainly didn't make a big deal of it except in a more general way which also involved scientists and data in all fields. There was certainly no "unprofessional behaviour" admitted or, indeed, any such accusations made in the programme. And there was definitely no hints of "dishonesty", "lieing" or any implications on him or his work - that is your opinion, which you no doubt held before the programme. The two interviewees who came off the worst were, as you mentioned, the journalist Delingpole but also Bob Carter - the latter looking seriously out of touch. Generally, the programme (to me) was a good example of the science and the scientists fighting back by presenting the evidence (as accepted by the vast majority of scientists), showing what the alternatives were (not a lot), and trying to win back the public from the idealogues and political interferers, especially from the media and various blogs - all mentioned, and shown, as untrustworthy and biased to their own agendas. Let's hope it is the start of scientists getting out there and showing the facts, to persuade the mass of the public who are presently confused by what they read from those who have little idea of the science in the first place.
  18. #41 LandyJim, I agree with you, it was an excellent program, and I look forward to seeing more of Nurse. And kudos to you for not wishing to try and stick up for Delingpole - the phrase "I am an interpreter of interpreters" will live for a long time with great amusement, especially as he admitted he hadn't even read any of the original science. But I must disagree with you over Phil Jones - he came across very well in my opinion, and gave a decent description of the splicing related to the hitherto utterly unremarkable WMO graph. Any accusations about scientific wrongdoing were perfectly well dealt with by the multiple independent reviews, and any complaints about the palaeoclimatic significance of the divergence problem have been dealt with in the literature. The more programmes we have like this showing the intellectual vacuity of the various AGW deniers, when they are confronted with rational evidence, and the weight of that evidence, the better!
  19. Skywatcher @35 (on other thread), Re Landy's comment: "Now they firmly believe they are correct in this assessment, but the fact is it is only a theory." Thanks for your eloquent explanation of "hypothesis" vs. "theory". I would add that climate science, despite the way "skeptics" and contrarians insist on trying and frame it, is not a belief system. The theory of AGW has been borne out by a multitude of independent lines of evidence assembled by thousands of scientists since 1824. What is very much "opinion" or "belief" or "hypothesis" is that we can radically change the composition of our atmosphere is a very short time with little or no negative consequence. The data (present, satellite record, instrument record and paleo) simply do not support that assertion. Landy also seems confused about consensus-- citing the predictable example of Galileo. That is, IMHO, no longer a valid argument. Today we have thousands of climate scientists working on this, and incredibly diverse and sophisticated instruments to monitor the planet. According to Dawkins, there is probably sufficient evidence now to refer to evolution as fact. And I would venture to say the same about AGW.
    Response: LandyJim, see "There is no consensus."
  20. Landy Jim, Please read Spencer Weart's excellent book "The Discovery of Global Warming". There is an extended online version available here. I highly recommend it.
  21. Landy Jim @41, "They are automatically labelled "deniers" and there have been instances of jobs threatened, papers refused to be published, careers damaged and even threats against the person." Absolute, unsubstantiated nonsense-- I strongly suspect that you have been reading contrarian blogs and/or highly inaccurate articles from certain media outlets. The people who have repeatedly received very real death threats, who are subjected to witch hunts, who have had their computers hacked (or fended off attempted hacks) are the climate scientists. I am more than happy to provide you with the abundant evidence of that. It strikes me as peculiar that you are trying to paint some "skeptics" as martyrs. Who are these martyrs? As for you claims about the FOI-- most of those "requests" were coming from overseas, Canada in particular. CRU did not and do not own the data in question and the people making the "requests" knew that-- why are we still having to explain these basic facts over a year later?! Failure to comply with some orchestrated vexatious FOI campaign (courtesy of Stephen McIntyre and friends)has nothing to do with wasting British tax payers' money. I would argue that what was a waste of money were the three investigations demanded by "skeptics" into the stolen email affair, which ultimately largely exonerated the people in question. I urge you to please read the report by Sir Muir Russel, the most comprehensive of all the investigations (here. The small group at CRU, overwhelmed, antagonized and under attack, made some bad calls and some people said some stupid things. Part of the problem was that the UEA failed the CRU by not providing sufficient guidance and administrative support to deal with the FOI requests. To my knowledge, well over a year has past yet McIntyre has yet to use those data that he demanded for anything, never mind a research paper. Does that not tell you anything Landy? "Let's hope it is the start of scientists getting out there and showing the facts, to persuade the mass of the public who are presently confused by what they read from those who have little idea of the science in the first place." And it is there that you Landy need to exercise some responsible and diligence. From what I have seen thus far you seem only too happy to believe the spin, disinformation and distortion being used by "skeptics", contrarians and those in denial about the theory of AGW. Well, you have no excuses for not fact checking their claims, and applying your skepticism equally. I apologize if my tone is terse, but I and others are getting rather sick and tired of having to repeat these basics (that are freely available for people to educate themselves), not to mention having to play whack-a-mole refuting the seemingly endless stream of misinformation that people have been fed by people with agendas.
    Response: Further discussion specifically of ClimateGate should be on "A retrospective of the Climategate retrospectives" or one of the other ClimateGate threads.
  22. I second Albatross. LandyJim's Theory: "Lets be honest here, some of the worst attacks on scientists have been those who have raised genuine and scientifically researched objections to AGW precepts." Show me the evidence. Show me A) "genuine and scientifically researched objections to AGW precepts," and B) that attacks have been made on "those" who have raised these objections. The precepts you're talking about are the well-established radiative physics of CO2, CH4, and H20. I've yet to see any alternative theory that describes the observed radiative properties of those molecules. What other precepts are you talking about?
  23. LandyJim, Calling on flat Earth ideas is underhanded, as these kind of theories were not based in real scientific investigation. even the early Egyptians had it right and were able to estimate the Earth curvature with decent accuracy, because they were using a real method. So the true scientific consensus on the shape of the Earth has been for round, and for more than 2000 years. "Only a theory" is the kind of language that creationists use to try to discredit evolution. It works only the general public, because science minded people know that the status of theory is the highest that an idea can reach in science. Saying that a set of ideas is "only" a theory is kind of an oxymoron. What could it be that's better? Theories are much farther reaching than mere laws. Real theories are seldom ditched altogether when new discoveries are made. Einstein did not even truly invalidate Newton, it expanded it and solved the problems that Newton couldn't get a handle on, such as Mercury's orbit. Newton's theory still works fine in its domain of application. It yields very precise results if you want to determine where a projectile is going to land. But it wouldn't allow for accurate GPS position reports. AGW is not a matter of opinion. The consensus model of Earth' climate is indeed a scientific theory and AGW is a normal consequence of it. That's not the opinion of the researchers, that's what the theory, based on countless research results, dictates. And, just like you said of evolution, there is really no alternative competent at integrating all these results, observations, data, analyses, in a coherent whole. There may be flaws or grey areas in the theory, as there is in any of them. It does not invalidate it. Only a more competent theory will do that. Even at that, a better theory will likely expand on it rather than replace it altogether.
  24. Landy Jim: Can you cite specific "instances of jobs threatened, papers refused to be published, careers damaged and even threats against the person" by scientific skeptics. We are all aware of climate scientists, like Phil Jones and many others, who have received death threats. James Hansen has documented in his book Storms of My Grandchildren that he has had grants cancelled because of his data on AGW. I have never heard of an instance fo a denier who has had grant issues or papers not published due to their content. Please provide specific instances or stop spreading false rumors.
  25. #41: " a few minutes of a 57 minute long program. Hardly scientific." I'm not aware of the term 'scientific' as applied to the watching of a television program. "Nurse presents a very balanced and unbiased view, bearing in mind he is a staunch advocate of AGW." There's a substantial fallacy in this need for a 'balanced view': If a body of evidence supports a conclusion, what 'balance' is created by discussing the opposite side? Do we say "Our observations show to a high degree of certainty that the earth is round, but some believe it may be flat"? That's background noise, which unfortunately gets picked up and amplified by the repeat-o-sphere. So your 'balanced presentation' does little more than provide deniers with ammunition (in this example, becoming the headline 'Scientists express doubt that the earth is round!') No, the message must be clear and unequivocal. If you are struggling to accept some aspect of AGW, despite the ample evidence presented here, by all means ask questions. But do not pretend that there is a 'balanced argument' to be made based on science -- if one existed, certainly we'd have heard it by now.

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