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Just what is this Consensus anyway?

Filed under: — group @ 22 December 2004 - (Français)

We’ve used the term “consensus” here a bit recently (see our earlier post on the subject), without ever really defining what we mean by it. In normal practice, there is no great need to define it – no science depends on it. But it’s useful to record the core that most scientists agree on, for public presentation. The consensus that exists is that of the IPCC reports, in particular the working group I report (there are three WG’s. By “IPCC”, people tend to mean WG I). Fortunately that report is available online for all to read at It’s a good idea to realise that though the IPCC report contains the consensus, it didn’t form it. The IPCC process was supposed to be – and is – a summary of the science (as available at the time). Because they did their job well, it really is a good review/summary/synthesis.

The main points that most would agree on as “the consensus” are:

  1. The earth is getting warmer (0.6 +/- 0.2 oC in the past century; 0.1 0.17 oC/decade over the last 30 years (see update)) [ch 2]
  2. People are causing this [ch 12] (see update)
  3. If GHG emissions continue, the warming will continue and indeed accelerate [ch 9]
  4. (This will be a problem and we ought to do something about it)

I’ve put those four points in rough order of certainty. The last one is in brackets because whilst many would agree, many others (who agree with 1-3) would not, at least without qualification. It’s probably not a part of the core consensus in the way 1-3 are. Most (all?) of us here on RealClimate are physical scientists – we can talk sensibly about past, present and future changes in climate, but potential impacts on ecosystems or human society are out of our field. If you want to see the IPCCs own summary, it’s here.

Other things we have mentioned in other posts come in as supporting evidence. That the increase in atmospheric CO2 is anthropogenic is so obvious that few people question it and in consequence few people rebut skepticism of it (though Eric has done so recently here; and the IPCC mention it). That the recent increase in temperature is unprecedented in the last 1000 years (see e.g. posts 64 or 7 by Mike) is one (but by no means the only) line of evidence indicating that recent change is likely to be unnatural (see update).

The skeptic attitude to consensus usually starts with “there is no consensus”. That’s wrong, and they usually retreat from it to “but consensus science is meaningless”, and/or “consensus has nothing to do with science”. The latter is largely true but irrelevant. The existence of the consensus doesn’t do a lot to determine what science is done; it doesn’t prevent contrary lines being explored. But the consensus view does come into the tricky interface between science and policy, and science and the media.

The existence of the consensus shouldn’t be used to hide the fact that there are areas of doubt. Climate models clearly aren’t perfect. There are questions about the differences between surface and tropospheric temperature trends. Conversely the existence of some areas of doubt shouldn’t be used to try to hide the many areas of understanding and agreement.

Update 2004/12/23: this post needs one correction and also clarification in a couple of places. Firstly, for point 1 I wrote “0.1 oC/decade over the last 30 years”. This is actually a bit of an understatement. 0.15 would be better, and the years since 2001 have been warm, pushing it up further. I’ve now replaced my first figure with the figure of 0.17 oC/decade since 1976, from the IPCC report.

For point 2, I wrote “People are causing this”. That was far too brief to cover the complexities concerned. Comments 5 and 6, and my responses, address this.

Lastly, I wrote “That the recent increase in temperature is unprecedented in the last 1000 years … is one (but by no means the only) line of evidence indicating that recent change is likely to be unnatural”. This is true, but incomplete and possibly misleading, in that it may appear to overstate the importance of the proxy record. If you follow the link to the TAR chapter 12, you’ll have found that the IPCC based its conclusion of human influence on climate on:

A longer and more closely scrutinised observational record
New model estimates of internal variability
New estimates of responses to natural forcing
Improved representation of anthropogenic forcing
Sensitivity to estimates of climate change signals
Qualitative consistencies between observed and modelled climate changes
A wider range of detection techniques

…and all of this lead them to write: The increase in the number of studies, the breadth of techniques, increased rigour in the assessment of the role of anthropogenic forcing in climate, the robustness of results to the assumptions made using those techniques, and consistency of results lead to increased confidence in these results. Detection and attribution have rapidly developed into an entire discipline and deserves its own post, sometime.

31 Responses to “Just what is this Consensus anyway?”

  1. 1
    tom says:

    A related issue is the position of the Bush administration that science cannot determine what level of warming is dangerous. I guess that sort of falls into category four. I take it that this statement
    by the administration is intended to suggest that nothing can be done until science can
    tell us what level of danger we should avoid. This is a no lose position for them because,
    inherently, I don’t think science can tell us what level of warming to avoid because it involves value judgments. It can tell us or attempt to tell us, however, about likely impacts. Just because science can’t tell me whether I should care about the disappearance of a species or the disappearance of glaciers doesn’t mean it is invalid for me to care.

    Another problem here is lack of honesty in the way the issues are framed, another problem that science can’t solve. I know I’m treading on being political, but I think it is important to point out what are scientific problems
    and what are not. The administration has hit on a neat position for them that can delay action indefinitely. Even they have conceded one through three, but feel they have a winner in a variation of four.

  2. 2
    dave says:

    >This will be a problem and we ought to do something about it

    Yes, this is a policy issue that is “outside” the scientific consensus. But, some scientists have made efforts toward defining what constitutes a “problem” or as Tom says, “what level of warming is dangerous”. (Always enjoy your comments, Tom).

    See the policy forum paper by O’Neill and Oppenheimer Dangerous Climate Impacts and The Kyoto Protocol published in Science vol. 296, pp. 1971-1972, June 14, 2002 here.

    Also, the next IPCC report is due in 2007. Meanwhile, various meetings/workshops are being held that provide new important results. By and large, these results are not seen by the public or policy makers, e.g. “Three Degrees of Consensus” by Richard Kerr, Science 2004 305: 932-934. This summary of the Paris “Workshop on Climate Sensitivity” (June 2004) reports that the polled climate models agree on a range of 2.5 to 4 degrees centigrade for doubled CO2. The low end as reported in the IPCC TAR is considered very unlikely while the high end remains poorly constrained. I point this out because there continues to be a disconnect between the “consensus” and the policy.

  3. 3
    eric says:

    I think this is an excellent update to my original post.
    I response to many of the comments written about that post, I would emphasize the general point that it is important to separate the question of the existence of a consensus from the question of the correctness of that consensus. Furthermore, the content of the consensus is really not as ambiguous as many would have you believe.

    Those who wish to argue the consensus is wrong would do better to find convincing ways to disprove the consensus view (which will be very hard to do, but we will all praise you as a great scientist if you succeed), rather than fruitless attempts to disprove the existence of the consensus itself (which will be impossible).

  4. 4
    Randolph Fritz says:

    “consensus has nothing to do with science”

    Quite the opposite. As Thomas Kuhn observed, scientific truth is what scientific consensus says it is. Many people want certainties to persuade them, and those science does not to have to offer; science is a human project, not the word of god. But when it comes to the physical world, the uncertainties of scientific consensus have proven consistently more accurate than any source perceived as certain.

    And this is a central problem of persuading people to act on scientific evidence. Science can never quite say “we know for sure”. But if, for instance, one is calculating the path of a cannonball, physics is what one to relies on if one wants to know when to duck. And perhaps some new & unexpected thing will happen and the cannonball will miss. But one does not stake one’s life on that!

  5. 5

    What does “people are causing this” mean? Does it mean people are responsible for all of the warming, most of the warming, some of the warming?

    “At least the majority of it” captures the consensus opinion, I believe. The possibility of the anthropogenic forcing being superimposed on a natural background cooling is not, as far as I know, excluded. Though it complicates the clarity of public communication, “more than all of it” is actually a possibility. Some people claim a solar warming forcing, but IPCC TAR does not see strong evidence of it as of 2001. See .

    [Response:: I think your comment must have crossed with my reply to JBS above, because I answer the same points there. From what I read of IPCC, the best estimate is of mild negative forcing from natural factors recently – William]

  6. 6
    James B. Shearer says:

    What does “people are causing this” mean? Does it mean people are responsible for all of the warming, most of the warming, some of the warming?

    [Response:: Fair question. My original phrasing was vague, mostly deliberately. If forced to be more precise, I would say the last 35 years definitely – this is the IPCC position (Ch 12 summary). Or the SPM says There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities. It depends a bit on whether you count from the re-start of the warming. I think there is less consensus over the early part of the century – a mix of anthro and natural seems to be agreed on, with some emphasising natural and some anthro. Natural seems to be preferred somewhat at the moment.

    That’s the answer time-wise. If you meant, what fraction of the recent warming is anthro, the current answer would seem to be “more than 100%” (see SPM fig 4), because the sum of natural forcings has been mildly negative over the last 50 ish years – William]

  7. 7
    GeniusNZ says:

    There is a 5) which is global warming may be bad – but it is NOT as bad as what it would take to prevent it.
    Eg you might say “to make a significant dent into global warming one would need to reduce fossil fuel consumption to zero by 2055 reducing by 2% per year. the effect of this is probably world wide depression rather like the 1930’s together with a requirement for an enforcement body and a few wars (since some countries will want to break the rules).
    I guess this solution would result in somwhere around a very long term 1 degree rise in temperature using a very rough extrapolating from the graph. 3.5 deg by 2100 for doing nothing and er about 3 for using Kyoto? maybe a bit less?
    Anyway the question is is the difference worth the cost.

    This is of course just an example – presumably the IF that was the case then one might argue that the

    I think (4) is worth expanding on.. do we have a reasonable consensus the effects of global warming?

    1) a significant amount of people in cold climates should benefit those in warm climates should be disadvantaged – possibly a little bit of migration as a result.
    2) Related to (1) the absolute amount of life on earth should increase (warmer tempratures and more CO2 -> more life generally speaking)
    3) BUT the amount of change should increace making it harder to manage – more people will thus fail to do this and there will be more crisis (eg ethipopian crisis) than there would have been otherwise.
    4) and because many animals cannot adapt as fast as humans – the diversity of species should decreace

    [Response: your point 5 is a perfectly valid one. In many senses the adaption-or-prevention debate is the debate we really should be having, since points 1-3 are now fairly well settled. The people at RealClimate are primarily qualified to talk about points 1-3. For the issues you raise re 4, my POV (and it isn’t much more than that – I’m no specialist in the consequences, other than sea level rise (shameless self promotional link there…)) – is that we (and the ecosystems that surround us) are likely to have problems coping with “rapid” changes from the current state that we have got used to. You say “a little bit of migration” – but in these days of national borders, that could be a major problem. Of course, its a political not a scientific one – William]

  8. 8
    Stephen Berg says:

    An interesting article on the obstructionist ways of the Bush Administration, their attempts to hinder scientific understanding of the issue:

  9. 9
    GeniusNZ says:

    RE 5
    I assume this must be the consensus
    2100 climate
    No change – 1.4 – 5.8 degrees change
    Kyoto Protocol 1.34-5.55 (I assume the .15 deg change is really a percentage of the average)
    Other solution ?-?

    I think this debate is important because if Kyoto will not prevent a disaster then we need to be very clear about it in the public debate that we need a better solution (so we can determine what that will entail) just as we need to oppose those who deny it is happening at all.

  10. 10
    Steve Bloom says:

    This seems as good a place as any to note what appear to me to be a couple of major problems with the IPCC approach:
    1) At the pace the science seems to be moving, six years seems to be too infrequent of an update schedule. For example, the IPCC assumption about the melt rate of Greenland has been thrown for a loop. Why wait two more years to incorporate such data? I may be misunderstanding things, but looking at the recent arctic study it appears that there’s a kind of research feedback loop where potentially out of date IPCC assumptions or conclusions are used with more current data to make additional conclusions which may then be too conservative.
    2) The 100-year timeframe used to predict warming impacts is too long. Humans do a whole lot better with a 50-year span (“lives of your children and grandchildren”), especially now that 50-year time frame predictions are starting to sound worse.

    [Response:: the 5/6 year upgrade cycle for IPCC does mean that the last report is somewhat out of date by the time the next appears. But this is just about inevitable. The work involved is large: if the reports were more frequent, it would be much harder to persuade people to contribute their time. As to 50/100 year projections: there is a habit of looking to 2100; but although IPCC says, e.g., “The globally averaged surface temperature is projected to increase by 1.4 to 5.8°C (Figure 5d) over the period 1990 to 2100” [1], if you look at fig 5d you can read off the temperature rise to 2050 or any desired date. Whether you should adjust the time horizon closer because predictions are looking worse is a difficult question – William]

  11. 11
    GeniusNZ says:

    what is the consensus (scientific as opposed to the chatroom consensus) on when oil reserves will run out?
    Since forecasting increased burning of oil to 2100 may be fundimentally flawed if oil/fossil fuels will run out in (lets say) 2060.

  12. 12
    dave says:

    Re: Steve Bloves’s remark:

    This seems as good a place as any to note what appear to me to be a couple of major problems with the IPCC approach:
    1) At the pace the science seems to be moving, six years seems to be too infrequent of an update schedule. For example, the IPCC assumption about the melt rate of Greenland has been thrown for a loop. Why wait two more years to incorporate such data? I may be misunderstanding things, but looking at the recent arctic study it appears that there’s a kind of research feedback loop where potentially out of date IPCC assumptions or conclusions are used with more current data to make additional conclusions which may then be too conservative

    Yes, things are looking bad in Greenland. See my incomplete story on this at Greenland Ice Sheet. There is no doubt that thinning (melting) of the Greenland Ice Sheet (and also the WAIS) is proceeding at rates beyond those predicted by the IPCC TAR (2001).

    When we speak of “The (De) Nile (denial)”, we are not just speaking of a river in Egypt.
    Sorry, that’s an old and bad joke.

    The bottom line is, these major ice sheets appear to be vulnerable to abrupt (non-linear) changes. And that’s what we may be seeing now.

    Well, we’re having some fun now, aren’t we?

  13. 13
    Tony Weddle says:

    I have a few comments and concerns about this article and some of the links.

    Others have commented on point 2 and, for me, this highlights that most of the concensus is based on statistical significance, based on what we know (obviously). Whilst we might be most certain that the rise in CO2 levels is anthropogenic, the rest of the concensus seems to be much less certain and based on the admittedly little we do know about factors affecting climate and what those interacting effects are. I read in Science (or Scientific American) magazine recently that no climate models are likely to be verified for another 50 years. So we are basing a concensus on models of unknown accuracy, and on historical data that is patchy and indirect. The most detailed data we have are only for the last 40 or 50 years.

    [Response:: I disagree with you over the degree of uncertainty you are asserting. That the rise of CO2 is anthropogenic is completely certain (or as certain as anything ever gets in science). For the rest, you say “admittedly little we do know”… you may admit to knowing little; we don’t. If you look in the IPCC report you’ll find definitions of the degrees of uncertainty relating to various items. As for verifying climate models: I think your meta-quote is garbled. Obviously, a 50-year prediction won’t be definitively verified until 50 years in the future: but this is simply obvious. To say that the models are of unknown accuracy is to ignore the evidence: try reading IPCC chapter 8; and the historical record is far better than you imply – William]

    Others have also commented on point 4, which is a value judgement. Given that we have poor models currently, surely we have no real idea of how much of a problem we have? The comment on requiring zero emissions is apt. This is impossible, given that we have to breathe and digest. Consequently, shouldn’t the priority be in trying to get accurate predictions of the effects of climate change, so that we can prepare for those effects?

    [Response: I won’t give you that we have poor models – William]

    Some of the reports also talk about “unnatural” factors, as though humans are not natural. This encourages an unhealthy attitude that humans and the rest of the universe are not compatible. Humans are as natural as bees and volcanos.

    [Response: if you want, you can call everything natural. Which makes the term useless. So we use the term in a way that makes it useful and that everyone understands: unnatural (or anthropogenic) is human-caused stuff – William]

  14. 14
    tom says:

    “attitude that humans and the rest of the universe are not compatible”

    Can’t speak for the rest of the universe, but it may very well be that human beings
    and the rest of the planet are,in reality, not compatible. It may take a catastrophe of
    planetary proportions to halt the expansion of human kind into the domain of the other
    species that feebly try to cohabit this planet. Mankind has a way of delaying what may be inevitable
    biological and ecological contraints on its fecundity. Other species run up against limits much earlier
    and dare I say naturally.

  15. 15
    Pat Neuman says:

    I feel that climate change is much more than an evironmental issue. I think climate change is an issue that will mean life or death for this planet. As such, it encompasses all other issues, … universal health care, worker rights, and so on…

    I think that many people are loosing sight of what’s important to them and to their families.

    I think that what’s missing for many people is that they have no clue about what’s really happening to the global climate. But I think people have a responsibility to find out what’s going on. They should know who to go to for advice, right?

    But the people don’t understand the serious consequences, mainly because the administrators, directors, and managers of government agencies that have responsibility to inform the public on safety are deliberately failing to show the public the consensus of science on the causes and consequences of rapid global climate change. I know this to be true. There is no doubt that the global climate is changing much too rapidly to sustain life. There is no doubt that the accumulation of greenhouse gases in the atmosphere due to machine power systems and excessive travel is driving rapid global climate change.

    I think a post that I made on Dec 14 shows that to be true, by the graphs of CO2 accumulation now happening in Earth’s atmosphere, the global temperature trends, the loss of ice in the Arctic, the shrinking glaciers throughout the world and many other fingerprints… all confirming the worst is likely or already in progress.

    There is no justification for excessive travel. It makes no sense to me that that some people think that they have to have been in places like Europe, Asia, Australia, even Africa, to have a meaninful lives. At what cost?

    My Dec 14 post to ClimateArchive, and other groups.

    Upward trend in atmospheric CO2 concentrations
    Climate Monitoring and Diagnostics Laboratory
    To obtain detailed understanding of the short term as well as long term variations of the greenhouse gases,…

    Upward trend in global temperatures

    2004: monthly and seasonal:
    January through August, 2004 were above normal. Sep 1, 2004 through Oct 31, 2004 global temperatures were the warmest on record (NCDC records since 1880). November was also the warmest on record, …
    Comparisons to previous years and averages are at:

    2003 annual:
    Annual global temperatures for 2003 are at:

    Time scale for global warming:
    The time scale for global warming is now, and for the future. Global warming is already influencing the intensity of rainfall according to observations in the Midwest and elsewhere.

    For more information…

  16. 16
    eric says:

    Update 26/12/2004: Naomi Oreskes has an op-ed in today’s Washington Post further discussing the topic of consensus.

  17. 17
    Ferdinand Engelbeen says:

    Re: #12 about the Greenland ice thinning:

    From NASA the flow of the largest glacier in Greenland doubled its speed in recent years. But that is hardly a matter of global warming, as Greenland temperatures were as high/higher in the period 1930-1940. After that, there was a cooling period until 1990, and a warming after 1990, just reaching the 1930-1940 period now.

    The temperature trends of Greenland can be seen at:

    As the Illulisat (Jacobshavn) temperature recording ceased in 1980, the temperature record of nearby Egedesminde can be used as representative for Illulisat too.

    Moreover, the receding of the glacier break-up point started in… 1850 (or maybe before) and the highest speed of receding was in the period 1929-1953, which includes the 1930-1940 period. See the detailed map (8 MB!) at or more compressed + discussion at:

    As one can see, it is not appropriate to make conclusions on too short time scales…

  18. 18
    TM Lutas says:

    One of the difficulties of sorting through neutral science and political polemic masquerading as science is that, to the layman, they sound so similar to untutored ears. There are a few markers. In a moderated forum, when off topic or explicitly political shots are moderated out when they come from one side of the argument but left in when the other side does them, it’s a pretty good marker that something’s not quite right as far as professionalism and neutrality is concerned. The previous article (comments closed) on consensus an example of this phenomenon.

    Comment #12 was edited as it was off topic from a denial point of view.
    Comment #19 was not edited or even much criticized though it was just as off topic from the other side.

    Comment #25 is interesting because the conclusion that it draws (that coal is the big problem, not oil) challenges the happy note #24 and the conspiratorialist #19 about equally but only explicitly challenges #24.

    Another marker for the layman of bias is an unwillingness to incorporate new information. The previous article’s comment #33 by Dennis Bray injected new data that demonstrates the weakness of the idea that there is an established consensus. Yet here we have a continued push in this thread, the idea of a well formed consensus for one clear position, when surveys of climatological experts point to a much more mixed picture with the bulk of respondents taking neither extreme as true.

    [Response: c12 was shortened, not removed entirely, becuse it was too long. Quite how much too long you don’t know (and nor do I). c19 is not much longer than the text left of c12. We are trying to be fairly inclusive about comments, but endless wurble has to be cut for the sake of our readers. c25 does indeed attack the happy note of c24 – which is the sort of marker you say you were looking for. c33 is interesting, but note that by “consensus” it is not asking the same question as I addressed in this post. The survey does not appear to have asked “do you agree that the IPCC report represents a consenus of sci opinion?”. The question c33 addresses may well deserve a longer answer elsewhere. As well as the specific points I raised in response there, is the what-is-the-question problem. “To what extent do you agree or disagree that climate change is mostly the result of anthropogenic causes?” is quite a vague question, depending on when you mean. If you meant, over the last 30 years, I think most would agree. Over the last century-150 years, you’d get about the response DB got. So, overall, I dispute your attempted marker, and indeed the assertion of trumpeting – William]

    These sorts of markers are not definitive. You may yet be right. The way that you present yourselves in your biases says that any truths trumpeted here should be treated as provisional at best.

  19. 19
    SkinnyPuppy says:

    I tend to agree with post #18 from TM Lutas. Having read many of these threads on realclimate, my impression is that the moderators are measurably selective as to which comments they insert a “[Response: …]” to correct, criticize, clarify, etc…

    On the Michael Crichton related threads, I observed that the moderators are very quick to make pedantic quibbles with posts supporting Crichton’s book or thesis, but largely ignore much less substantial posts that attack his position.

  20. 20
    Tony Weddle says:

    Following William’s reponse to my comments, I’d like to add the following.

    Yes, we do know a lot about climate, but all the scientific articles I read lead me to think that there is more that we don’t know.

    [Response: That seems odd to me. Have you tried reading the IPCC report? Which scientific articles have you read that contradict it? – William]

    We understand some of the factors affecting climate but are not certain just what those effects are, or how those factors combine. There are also undoubtedly other factors that we haven’t yet included in models.

    [Response: Here you are doing the good old “emphasising the uncertainties” approach. If you take this approach seriously, then you should be *more* worried about climate change, not less, because the upper range of effects becomes larger. As to “undoubted” other factors – if you mean important ones – then no: it is not true that there are factors that are undoubtedly important that are missing. Tough there might be factors that might be important… – William]

    I think I was accurate, and not “garbled”, in quoting a minimum of 50 years before we can hope to validate the models we’re using, if we ever can. Most of the data that estimates are based on is only detailed over the last 50 years or so. The famous hockey stick gets increasingly uncertain as we go back in time, since we rely on indirect and less extensive measurements than we are making now. Indeed, the acknowledged uncertainties in the hockey stick diagram, could lead to completely opposite views to what appears to prevail these days.

    [Response: It would be better to find the exact quote, rather than relying on ever-fallible memory – William]

    [Response #2: It is not the case that “acknowledged uncertainties in the hockey stick diagram, could lead to completely opposite views to what appears to prevail these days. ” Rather, numerous independent reconstructions and model estimates support the contention that late 20th century warm is anomalous in the context of at least the past 1000 years, taking into account the estimated uncertainties. We refer you to our detailed piece on the hockey stick here. – Mike]

  21. 21
    Akshay says:

    The current IPCC consensus on the cost/benefits of adaptation/mitigation seems to be that there is very little consensus. “A little bit of climate change creates winners and losers, a lot of it is bad for almost everyone. Third world countries and the poor are likely to suffer the most.” Reading the relevant chapter of the “Impacts” volume gave me the *subjective* impression that 3.5C warming is deemed acceptable by the most optimistic “reasonable” economic models. There are good arguments for thinking this is optimistic, however, and other models advocate far more stringent action. The cost-benefit analyses are extremely sensitive to certain assumptions. But perhaps IPCC 2007 or 2013 will dare define an “upper bound” of reasonable opinion on what climate change we can adapt to.

    Another point that might be included in your consensus FAQ is past rapid climate change: “In the last 400.000 years, there have been episodes of very rapid climate change, for instance a warming of X degrees in several decades.” While this is not very informative about the future, the mere possibility of climate surprises seems important.

    [Response: I don’t feel qualified to comment on the ecological/societal impacts. It might be a valuable subject for a guest editorial though, since it is a reasonable question (in many ways its the question we really ought to be getting onto, but unfortunately we have to convince the skeptics about what is well known first).

    Past rapid change is another good point. AFAIK (and this is another one I shall disclaim expertise on) past rapid changes are associated with large ice sheets over North America, ie during glacial times only – William]

  22. 22
    Tony Weddle says:

    Thanks to William for his responses to post 20.

    I wasn’t referring to scientific reports that contradict the IPCC report (though there may be some) but to reports that often emphasise the uncertain nature of the analyses we’re doing. We seem to learn about new factors that affect climate fairly frequently and modelling how all the various known factors (never mind the unknown factors) interact is an impossible exercise.

    [Response: In #20 I asked you which scientific papers you meant, and you didn’t answer. Which ones do you mean? If you mean, “we learn new things which upset the standard picture” fairly frequently, then I disagree. What do you have in mind here? – William]

    I don’t actually worry about global warming, whether it accelerates or not, though for reasons which are not relevant to this article. I do worry about the impression that the general population is given, that climate change can be stopped.

    On another point, I read that there is evidence from the different ice core surveys that CO2 levels lag temperature changes (they rise after temperature rises and fall after temperature decreases). Is this true?

    [Response: People get rather interested in this, but its not as relevant to the current situation as many seem to supposeCertainly, it forms no part of the consenus I’ve described. In the current case, we *know* that the CO2 increase is caused by people, we observe warming, and we predict more (conditional on further CO2 increases, etc). In the case of interglacial cycles the forcing is astronomical and the lag/lead situation between CO2 and T is less clear. Its also hard to do: the T signal comes from delta-O-18, which is in the ice; but the CO2 comes from the trapped air bubbles, which don’t have the same age as the ice that surrounds them (due to close-off time) – William] [We do know a bit more about the CO2/temperature lag/lead for some parts of the record and we have a post on this: see What does the lag of CO2 behind temperature in ice cores tell us about global warming? by guest writer Severinghaus. — eric]

  23. 23
    Tony Weddle says:


    I think all the scientific papers and articles I’ve looked at include a statment of uncertainties.

    Even the IPCC report talks about uncertainties and the predicted temperature increase is in a fairly wide range, given the temperature increase for the last century. For example Quantification of modelling uncertainties in a large ensemble of climate change simulations, Nature 430, 768 – 772 (12 Aug 2004) reduces this to “5-95 per cent probability range of 2.4-5.4 °C” and also mentions “owing to large but unquantified uncertainties in the modelling process”, whilst Atmospheric science: Tropospheric temperature series from satellites, Nature 432, (02 Dec 2004) Brief Communications says “We believe that their approach overfits the data, produces trends that overestimate warming and gives overly optimistic uncertainty estimates.” Others imply uncertainties. For example, Human contribution to the European heatwave of 2003, Nature 432, 610 – 614 (02 Dec 2004) Letters to Nature says “it is possible to estimate by how much human activities may have increased the risk of the occurrence of such a heatwave”

    So all I was indicating is that the uncertainties are well known to researchers but perhaps not so well known to the public.

    [Response: Yes of course. But that is a very different thing to your previous “admittedly little we do know about factors affecting climate and what those interacting effects are”, with which I would disagree, as I did – William]

    Your comment on the lag or otherwise of CO2 to temperature gives an impression that you regard it as unimportant, forming no part of the concensus. But if CO2 concentrations are largley the result of temperature increases, rather than the other way round, doesn’t this throw the concensus predictions into question?

    [Response: No, not at all. We *know* that the current CO2 rise is anthropogenic (and you’ve agree with this before) so the interesting question is, “what happens when increases in CO2 are the forcing?” And the answer is, temperatures rise, as far as we can tell. The question, “what happens when orbital effects are the forcing” isn’t very interesting at the moment. There *is* some concern that increasing temperatures would lead to a further feedback of increasing CO2, of course – William]

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    Tony Weddle says:

    Thanks to William and Eric, for the replies. That link on the CO2 lag was excellent and certainly puts things in a different light. However, it makes we wonder what stops the warming process.

    By the way, William, I didn’t agree that the current CO2 rise is anthropogenic, just that there is a, probably significant, anthropogenic factor.

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    J. Sperry says:

    Since I haven’t seen a ‘trackback’ post yet, William’s article above is discussed in last week’s article by Iain Murray. Briefly, his argument is that:

    “[Naomi] Orsekes has therefore cheerfully elided a genuine consensus on points 1 and 2 of [William] Connolly’s definition into an assertion that this mandates policy action. It can do no such thing.”

    So, I think the consensus is (or should be) that humans have some degree of influence (pun intended) in an ever-changing climate, which may or may not lead to catastrophic effects at some point in the future.

    (And I cheerfully await another ad hominen reply on how I should have gotten a better source than Iain Murray.)

    [Response: have we been biting? Sorry. Anyway, thanks, I saw the TCS link… I’m delighted they have picked up on us. That particular IM piece is fairly sane and thoughtful. But wrong in some key places. Attempting to assert that Singer, for example, would agree with the consensus is not plausible. Accepting *some* anthro influence is becoming the lastest skeptic trick to say yes-look-we’re-reasonable. Accepting a recent warming of say 0.017 oC/decade with primarily anthro cause is another matter (I disagree with Pielke’s piece over this distinction, BTW). And the IM quote you provide above is a misrepresentation of Oreskes position – William]

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    Global Warming: Framing the debate
    Oil firms fund campaign to deny climate change: Lobby groups funded by the US oil industry are targeting Britain in a bid to play down the threat of climate change and derail action to cut greenhouse gas emissions, leading scientists…

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    […] RealClimate: Just what is this conensus anyway? […]

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    […] minority of scientists who are funded by the very worst elements of the fossil fuel industry. This 2004 article explains the […]

  30. 30

    […] of the Intergovernmental Panel on Climate Change, particularly targeting the conclusion that a scientific consensus considers global warming a real—and […]

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    […] here for another discussion of what the consensus is all about. A bit more technical description is […]