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The IPCC AR5 attribution statement

Filed under: — gavin @ 10 October 2013

Last year I discussed the basis of the AR4 attribution statement:

Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.

In the new AR5 SPM (pdf), there is an analogous statement:

It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together. The best estimate of the human-induced contribution to warming is similar to the observed warming over this period.

This includes differences in the likelihood statement, drivers and a new statement on the most likely amount of anthropogenic warming.

It is useful to remind ourselves that these statements are addressing our confidence in the characterisation of the anthropogenic contribution to the global surface temperature trend since the middle of the 20th Century. This contribution is unavoidably represented by a distribution of values because of the uncertainties associated with forcings, responses and internal variability. The AR4 statement confined itself to quantifying the probability that the greenhouse-gas driven trend was less than half the total trend as being less than 10% (or alternately, that at least 90% of the distribution was above 50% based on the IPCC definition of “very likely”):

Figure 1: Two schematic distributions of possible ‘anthropogenic contributions’ to the warming over the last 50 years. Note that in each case, despite a difference in the mean and variance, the probability of being below 50, is exactly 0.1 (i.e. a 10% likelihood).

In AR5, there are two notable changes to this. First, the likelihood level is now at least 95%, and so the assessment is for less than 5% probability of the trend being less than half of the observed trend. Secondly, they have switched from the ‘anthropogenic greenhouse gas” driven trend, to the total anthropogenic trend. As I discussed last time, the GHG trend is almost certainly larger than the net anthropogenic trend because of the high likelihood that anthropogenic aerosols have been a net cooling over that time. Both changes lead to a stronger statement than in AR4. One change in language is neutral; moving from “most” to “more than half”, but this was presumably to simply clarify the definition.

The second part of the AR5 statement is interesting as well. In the AR4 SPM, IPCC did not give a ‘best estimate’ for the anthropogenic contribution (though again many people were confused on this point). This time they have characterised the best estimate as being close to the observed estimate – i.e. that the anthropogenic trend is around 100% of the observed trend, implying that the best estimates of net natural forcings and internal variability are close to zero. This is equivalent to placing the peak in the distribution in the above figure near 100%.

The basis for these changes is explored in Chapter 10 on detection and attribution and is summarised in the following figure (10.5):

Figure 2. Assessed likely ranges (whiskers) and their mid-points (bars) for attributable warming trends over the 1951–2010 period due to well-mixed greenhouse gases (GHG), other anthropogenic forings (OA), natural forcings (NAT), combined anthropogenic forcings (ANT), and internal variability. The HadCRUT4 observations are shown in black with the 5–95% uncertainty range due to observational uncertainty.

These estimates are the “assessed” trends that come out of fingerprint studies of the temperature changes and account for potential mis-estimates (over or under) of internal variability, sensitivity etc. in the models (and potentially the forcings). The raw material are the model hindcasts of the historical period – using all forcings, just the natural ones, just the anthropogenic ones and various variations on that theme.

The error bars cover the ‘likely’ range (33-66%), so are close to being ±1 standard deviation (except for the observations (5-95%), which is closer to ±2 standard deviations). It is easy enough to see that the ‘ANT’ row (the combination from all anthropogenic forcings) is around 0.7 ± 0.1ºC, and the OBS are 0.65 ± 0.06ºC. If you work that through (assuming normal distributions for the uncertainties), it implies that the probability of the ANT trend being less than half the OBS trend is less than 0.02% – much less than the stated 5% level. The difference is that the less confident statement also takes into account structural uncertainties about the methodology, models and data. Similarly, the best estimate of the ratio of ANT to OBS has a 2 sd range between 0.8 and 1.4 (peak at 1.08). Consistent with this are the rows for natural forcing and internal variability – neither are significantly different to zero in the mean, and the uncertainties are too small for them to explain the observed trend with any confidence. Note that the ANT vs. NAT comparison is independent of the GHG or OA comparisons; the error bars for ANT do not derive from combining the GHG and OA results.

It is worth asking what the higher confidence/lower error bars are associated with. First, the longer time period (an extra 5 years) makes the trends clearer relative to the noise, multiple methodologies have been used which get the same result, and fingerprints have been better constrained by the greater use of spatial information. Small effects may also arise from better characterisations of the uncertainties in the observations (i.e. in moving from HadCRUT3 to HadCRUT4). Because of the similarity of patterns related to aerosols and greenhouse gases, there is more uncertainty in doing the separate attributions rather than looking at anthropogenic forcings collectively. Interestingly, the attribution of most of the trend to GHGs alone would still remain very likely (as in AR4); I estimate a roughly 7% probability that it would account for less than half the OBS trend. A factor that might be relevant (though I would need to confirm this) is that more CMIP5 simulations from a wider range of models were available for the NAT/ANT comparison than previously in CMIP3/4.

It could be argued that since recent trends have fallen slightly below the multi-model ensemble mean, this should imply that our uncertainty has massively increased and hence the confidence statement should be weaker than stated. However this doesn’t really follow. Over-estimates of model sensitivity would be accounted for in the methodology (via a scaling factor of less than one), and indeed, a small over-estimate (by about 10%) is already factored in. Mis-specification of post-2000 forcings (underestimated volcanoes, Chinese aerosols or overestimated solar), or indeed, uncertainties in all forcings in the earlier period, leads to reduced confidence in attribution in the fingerprint studies, and an lower estimate of the anthropogenic contribution. Finally, if the issue is related simply to an random realisation of El Niño/La Niña phases or other sources of internal variability, this simply feeds into the ‘Internal variability’ assessment. Thus the effects of recent years are already embedded within the calculation, and will have led to a reduced confidence compared to a situation where things lined up more. Using this as an additional factor to change the confidence rating again would be double counting.

There is more information on this process in the IPCC chapter itself, and in the referenced literature (particularly Ribes and Terray (2013), Jones et al (2013) and Gillet et al (2013)). There is also a summary of relevant recent papers at SkepticalScience.

Bottom line? These statements are both comprehensible and traceable back to the literature and the data. While they are conclusive, they are not a dramatic departure from basic conclusions of AR4 and subsequent literature – but then, that is exactly what one should expect.


  1. A. Ribes, and L. Terray, "Application of regularised optimal fingerprinting to attribution. Part II: application to global near-surface temperature", Clim Dyn, vol. 41, pp. 2837-2853, 2013.
  2. G.S. Jones, P.A. Stott, and N. Christidis, "Attribution of observed historical near-surface temperature variations to anthropogenic and natural causes using CMIP5 simulations", J. Geophys. Res. Atmos., vol. 118, pp. 4001-4024, 2013.
  3. N.P. Gillett, V.K. Arora, D. Matthews, and M.R. Allen, " Constraining the ratio of global warming to cumulative CO 2 emissions using CMIP5 simulations ", Journal of Climate, pp. 130314153438000, 2013.

73 Responses to “The IPCC AR5 attribution statement”

  1. 51
    Mal Adapted says:

    Ray Ladbury:

    I can equally cite prominent leftists who are in denial–the most prominent may have been the late Alexander Cockburn.

    Ray, seriously? I realize a left-right (or Democratic vs. Republican) axis is imperfectly mapped onto the spectrum of motives for AGW denial, but if the Democratic party is “left” and the Republican party is “left”, the weight of denial looks pretty right-heavy to me.

  2. 52
    Anonymous Coward says:

    Greg Simpson (#50),
    My understanding is that A stands for the sensitivity of average temperatures to an abstract generic forcing.
    So A can not be zero because that would imply an infinitely strong negative feedback which somehow makes forcings irrelevant.

  3. 53
    Patrick 027 says:

    phytoplankton take up CO2 and make organic C in the upper ocean as nutrients allow; then some sink – if they make it all the way without oxidizing, organic C is stored on the seafloor, taken out of the ocean+atmosphere. Otherwise, oxidation occurs along the way (as allowed by dissolved O2, presumably, so a given mass of subsurface water can only oxidize so much of the organic C falling into it). If the rate of this sinking and oxidation increases, or if it sinks into water which has farther to go before upwelling, more CO2 will be stored in the deep ocean.

    But more CO2 would make the water more acidic, and maybe it would dissolve more of the CaCO3 shells that may also be falling through it (?) (or dissolve it from the seafloor?) … so when it upwells again, maybe it wouldn’t release so much CO2 back into the atmosphere.

    (And what about if so much plankton with CaCO3 is sinking, depleting the upper waters of Ca and causing the surface water to release CO2 (bicarbonates turning to carbonate and CO2)?)

    Seawater chemistry is complicated. Skepticalscience has a series of posts on it.

    because of very low O2 abundance in the atmosphere in the Archean eon, CH4 could have built up to much higher levels than now. An idea was proposed that oxygenic photosynthesis combined with methanogens would result in a build up of CH4. Unlike H2O, which drops ‘precipitously’ with altitude, CH4 is not trapped in the lower atmosphere as such and would reach heights where photochemical reactions … etc, H escape to space would be enhanced, leaving C behind; that C could oxidize but there would be a build up of O2 owing to the H escape. (At first, O2 build up in the atmosphere could have been prevented due to O2 sinks – ferrous Fe in the ocean being one (reaction produces ferric Fe, which is less soluble and formed the banded iron formations, which are now used as Fe ore). Eventually O2 could accumulate in the atmosphere – however there may have/was? a period of anoxic deep oceans prior, which I think may have been sulfidic (due to atmospheric O2′s effects on the S cycle? – not sure offhand)

    on CH4′s role in oxygen build-up:
    David C. Catling, Kevin J. Zahnle, Christopher P. McKay “Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of Early Earth” “Science 3 August 2001: Vol. 293 no. 5531 pp. 839-843 DOI: 10.1126/science.1061976″

    on sulfidic deep oceans:
    Canfield, ‘A new model for Proterozoic ocean chemistry” “Nature 396, 450-453 (3 December 1998) | doi:10.1038/24839; ” ,

    Timothy W. Lyons, Christopher T. Reinhard, “An early productive ocean unfit for aerobics” “PNAS October 27, 2009 vol. 106 no. 43 18045-18046 ” “Published online before print October 21, 2009, doi: 10.1073/pnas.0910345106″
    2nd paragraph describes the biological pump (the sinking of biomass in the ocean), and subsequent paragraphs describe how atmospheric O2 would lead to sulfidic deep oceans; the rest is quite interesting (I’ve read down to fig.1, and just found out that “cyanobacteria, well-known perpetrators of oxygenic photosynthesis and the organism credited with the first oxygenation of the atmosphere, can switch to anoxygenic photosynthesis under euxinic conditions and subsist on H2S.


    With CH4 built up in the atmosphere, if, as I recall, by atoms, the C to O ratio exceeded 1 (right?), an organic haze would form, and could act as a UV shield, but would also have a cooling effect.

    Back to the greenhouse effect – with more CH4, less CO2 would be needed to counter the ‘faint young sun’ effect (along with increased land albedo owing to lack of forests, etc, … but of course, land area changes over geologic time (sometimes vast parts of continents are flooded)).

    CH4 is less ‘dependable’ than CO2 – emit some O2 and levels drop. If it is sustained in the presence of much O2 (so that atmospheric residence time is ~20 years rather than ~1000 years or … I think I read 10,000 years as being possible for near zero oxygen), then a drop in the source leads to a quick drop in CH4 abundance. There’s also the ‘clathrate (hydrate) gun hypothesis’ – for PETM (although how much of that actually came into the atmosphere as CH4, I don’t know).

    It would generally take a long time for the negative chemical weathering feedback to respond, so a quick drop in CH4 has been suggested as an instigator in Snowball Earth episodes (another idea is that clustering of continents near the equator could maintain greater chemical weathering as the polar regions cool). Oxidation of CH4 produces CO2 – if it is an increase in oxidation that is the cause, then some CO2 is produced to partly offset the effect – although some of that will go into the ocean (that would have a net effect on atmospheric CH4+CO2 assuming CH4 solubility in water is smaller, which I’m guessing it is although I’ve not seen numbers). There could still be a large decrease in the greenhouse effect, but only if CH4 is starting at, or decreases to a relatively small concentration compared to CO2. At present, each additional molecule of CH4 has a much stronger warming effect than each additional molecular of CO2 (at least instantaneously; taking into account the longevity of CO2 changes alters the picture – more so if the CH4 is emitted in place of what would have been CO2, rather than CH4 from a net loss of organic C or from fossil C); but this is only because there is so much more CO2. If CO2 and CH4 were equally abundant, the CO2 would be the stronger greenhouse gas.

  4. 54
    Patrick 027 says:

    re Greg Simpson @ 50

    There are forcings, from changes in CO2, aerosols, etc. The surface and tropospheric temperatures tend to respond in proportion to tropopause-level radiative forcing after stratospheric adjustment (although somewhere above I read they did something different about the stratosphere this time?)… and for the same global average forcing, nearly the same global average response may be expected (aside from the differences in the initial stratospheric adjustment), with nearly the same ‘shape’ (seasonal and latitudinal, regional, height, etc. changes in temperature and other things), if the shape of the feedback to the temperature change has a much stronger effect than the shape of the forcing. But the shape of the forcing may be different enough (esp. including stratospheric effects in some cases) to have a fingerprint in the shape of the response.

    If you think of the shape as being represented by a direction in (n-dimensional) space, then the response is a vector, and some vectors may have perpendicular and parallel components (two perpendicular vectors would be orthogonal functions).

    If I understood Gavin @ 41 correctly:

    Based on modeling (right?), the shape of the response to CO2, sCO2, is A+b, and the shape of the response to aerosols, sAero, is A+c, where A is the component which is parallel (now I realize there is a problem here, because you could just find the component of sAero parallel to sCO2, set that equal to c, and make b=0. So maybe this isn’t the best way to describe it?)

    Thus, if A is much larger than b and c, the shapes of the responses will be similar and a fingerprint analysis will have trouble distinguishing the two contributions from the total, which has been observed to be the shape A+e.

    X is the size of the response to the CO2 forcing, -Y is that for aerosols, and d is the size of the total response (of those two), so X*(A+b) – Y*(A+c) = d*(A+e).

    (if my vector analogy was confusing or in error, then for illustrative purposes only (because this is most likely not true (and it isn’t restricted to temperature changes), but an example of the kind of thing being described, I think): suppose A is a global average temperature change of 0.5 K plus 0.2 K * sin(longitude), and b = 0.01 K * sin(2*longitude), and c = 0.01 K * sin(2*latitude) (because legendre polynomials don’t come to me so fast), and e = …?

    So if X(A+b) – Y(A+c) = d(A+e), then (X-Y)*A = d*A, thus X-Y = d, which by itself doesn’t allow us to solve for X and Y. We could also look at X*b – Y*c = d*e; now for that to be true, e has to be a linear combination of b and c (a linear superposition of the functions of latitude and longitude just mentioned above), and we could divide e between those two components and solve for X and Y – but apparently these components are too small to do this with simultaneous precision and confidence. So we are left with some significant uncertainty about X and Y, greater than the uncertainty in their total.

    Is this right?

    Of course, if X can be farther constrained by the modeling of the forcing itself, that could be combined to further constrain Y, right?

  5. 55
    Jim Larsen says:

    42 SecularA said, “Denial of anthropogenic global warming has nothing whatsoever to do with being “economically right-wing”, or with any other economic or political ideology.”

    Total trash. There is a seriously strong relationship between Republicanism and Denialism. My entire family is Republican and Denialist, as is every Republican I know. Of course there are exceptions, but the relationship holds.

  6. 56
    Patrick 027 says:

    … re my last comment – while not necessary for the point being made, I should have multiplied any sinusoidal function of longitude by a function of latitude (ideally based on a Legendre polynomial) such that it would be zero at the poles; also replace sin(2*latitude) with sin(latitude) or cos(2*latitude) so it’s smoother at the poles … etc.

  7. 57
    Sean says:

    @55 Jim, the exception always proves the rule. I’m surprised by the reaction, as I thought it would be obvious. I realise there is a ban on posting political content here, and that’s not my intent to be pro-con either side here. Hopefully the following basic information is acceptable. It is only a quote from Wiki. Anyone can check the references and do more research themselves to check the validity of the following quotes:

    Political identification
    In the United States, support for environmental protection was relatively non-partisan in the past. Republican Theodore Roosevelt established national parks whereas Democrat Franklin Delano Roosevelt established the Soil Conservation Service. This non-partisanship began to erode during the 1980s when the Reagan administration described environmental protection as an economic burden. Views over global warming began to seriously diverge between Democrats and Republicans during the negotiations that led up to the creation of the Kyoto Protocol in 1998.

    In a 2008 Gallup poll of the American public, 76% of Democrats and only 41% of Republicans said that they believed global warming was already happening. The gap between the opinions of the political elites, such as members of Congress, tends to be even more polarized.[10] and

    In the United States, ideology is an effective predictor of party identification, where conservatives are more prevalent among Republicans, and moderates and liberals among independents and Democrats. A shift in ideology is often associated with in a shift in political views.[13] For example, when the number of conservatives rose from 2008 to 2009, the number of individuals who felt that global warming was being exaggerated in the media also rose.[14]

    A personal observation of my own as a non-American: On the traditional band of Left/Right political ideology the USA overall would sit far to the right of most of world nations including Europe and the OECD. Putting that another way, the average Democrat supporter/politician would be to the Right of Center of most other English speaking, OECD, advanced Asian societies and South American nations. Republicans would sit to the extreme Right.

    Sometimes being too close to something gets in the way of seeing it clearly. thx Sean

  8. 58
    Ray Ladbury says:

    Mal Adapted and Sean,
    You miss the point–the fact that there are prominent, smart folks on both extremes of the political divide (and you can’t get much more extreme than Alexander Cockburn) who are in denial means that the left-right distinction is not particularly useful in such discussions. Likewise the fact that prominent conservatives admit the severity of climate change (e.g. Colin Powell).
    Conservation ought to be a mainstream if not a default position for conservatives. The conservatives in the US have been taken over by a radical fringe–the drill-baby-drill crowd. My parents are life-long Republicans, fiscal conservatives, etc. The party left them, and they only stay in it to piss off the teabaggers.

    The question that is interesting is why this has occurred and whether true conservatives can reclaim their party by getting it to acknowledge physical reality again.

  9. 59
    SecularAnimist says:

    Jim Larsen wrote: “There is a seriously strong relationship between Republicanism and Denialism.”

    Which has absolutely nothing to do with any actual inherent political, social, or economic tenets of “Republicanism”, and everything to do with the fact that fossil fuel interests have heavily favored Republican politicians with campaign contributions and have heavily targeted Republican voters with denialist pseudo-science and pseudo-ideology.

    The crackpot nonsense and blatant lies that denialist politicians like James Inhofe spew do not arise from any real ideology. They arise from a script that he is handed and paid to read from.

    The crackpot nonsense and blatant lies that denialist “trolls” spew on blogs everywhere also do not arise from any real ideology. They arise from a script that is spoon-fed to them by the fossil fuel-funded denialist media.

    Global warming denial is not a spontaneously arising, grassroots phenonenon — it is completely top-down, driven by the funding from the fossil fuel corporations. The fact that they are making particularly effective use of the “Fox News base” of the Republican Party is simply a matter of convenience.

  10. 60
    Radge Havers says:

    @ 58 (and others)

    Good question. And how to addess it? There seem to be some ad hoc blockages to change in the party’s structural drivers (ALEC, Heritage Foundation, etc.). Money to be sure, but there’s more going on here than just the oil companies. From where I sit, it looks like the consequences of a long history of political strategies that have aggravated issues that never got resolved in the1800′s — everything from manifest destiny to the implications of Darwin and the views of rustic, evangelical fabulists; not to mention attitudes and fears, pro and con, about industrialization. On and on it goes.

    It’s a pickle, I tell you! In any case, it’s probably healthy to be skeptical of mono-causal explanations, seductive though they may be.

  11. 61
    Anonymous Coward says:

    There is a blog where regular commenters dismiss papers published in Nature Climate Change and elsewhere without reading them or even having a clue as to what they actually contain.
    They expound on their preconceived ideas and attempt to justify their short-sighted politically-motivated conclusions with anectodesal evidence and conspiracy theory.
    Am I talking about WUWT? No, Real Climate. If it’s not physics, anything goes!

  12. 62
    Ray Ladbury says:

    AC, citation fricking needed.

  13. 63
    Mal Adapted says:


    Global warming denial is not a spontaneously arising, grassroots phenonenon — it is completely top-down, driven by the funding from the fossil fuel corporations.

    As I see it, AGW deniel is largely but not completely top-down driven. The unwillingness of Americans to pay costs that historically have been kept external to their personal prosperity, or even to acknowledge that they exist, is a powerful motivation for AGW denial. The FF-industry funded campaign exploits and amplifies that tendency in psychologically unsophisticated individuals; but the tendency itself, if not inborn, is learned early in life. Once acquired it is difficult to overcome, even without relentless reinforcement.

  14. 64
    Sean says:

    Stumbled upon this from Yale Project on Climate Change Communication.
    Climate Change in the American Mind: Focus on California, Colorado, Ohio and Texas – See more at:

    It probably belongs better in the Nov. Unforced Variations slot, and if I remember I will repost it there (?)- apologies for the off-topic distraction to Gavin’s article which I seem to have started here. Mea Culpa – I meant well, as ongoing dis-information is my main interest. Best to all.

  15. 65
    Patrick 027 says:

    re 48 Ray Ladbury “but rather that political philosophy by itself is not predictive or useful.” maybe not in an absolute sense, but statistically,… “If we are to cleave to truth, we cannot cling to ideology–regardless of the ideology.” Of course, if you make it your ideology to not be blinded by ideology, that is an ideology that would make it more likely to find truth, would it not?

    e.g. the ‘all government is bad’ crowd would be more likely to deny a problem where some use of government would be a sensible solution, then the ‘government is bad, … except when it’s good’ crowd (unless they just mean, ‘when it’s good for me’). It’s not a surprise that a political wing which wants smaller government would be less likely to want to deal effectively with pollution, etc. OTOH, GMOs … for which I am still somewhat on the fence, though I am aware there are at least some anti-GMO statements which don’t hold up, but I’m not sure if being anti-GMO is really at the forefront of the left (center-right as opposed to far right – thanks Sean). (I once, out of morbid curiosity, took a book by Newt G., found the section on science, and was … let’s say, amused … that of his examples of left-wing science errors, some were actually, or have become to some extent, right-wing, or at least, his right-wing errors (ozone, AGW), and the only two that were right that I recall: GMOs (not as pervasive or clear-cut as AGW?) and vaccines (seems rather fringe to me). Basically I think the left-wing fringe has stayed fringe while the right-wing fringe has become more mainstream.

    … and what Radge Havers and others said. (PS there has been somewhat of a flip-flop: In part 4 of “(the?) Men Who Built America”, a scene where the top 3 robber barrons of the late 1800s discuss the threat of Cross-o’gold WJB, and one points out he doesn’t believe in evolution. Rockeffeler seemed to embrace it (that’s the impression I got) (though did he understand it? not sure); also he was a religious man (as was WJB, as I recall). Interesting show. Anyway…

  16. 66
    SecularAnimist says:

    Mal Adapted wrote: “The FF-industry funded campaign exploits and amplifies that tendency in psychologically unsophisticated individuals …”

    Well, yes. Of course. Effective propaganda works by targeting existing “tendencies”, weaknesses and vulnerabilities in its audience. And a lot of money, time and effort is invested in finding those “tendencies” and learning how to effectively exploit them — through focus groups, for instance.

    This is, after all, exactly what the “Mad Men” of Madison Avenue have been doing for generations: finding people’s buttons and pushing them.

    And in the Republican base / Fox News / Rush Limbaugh audience, you have a large group of people whose buttons have been thoroughly mapped out and reliably programmed to the point where the Mad Men can simply proclaim to them that global warming is a “liberal hoax” perpetrated by “Al Gore”, and brand denialism as a “conservative” value, and they will absolutely and unquestioningly embrace every word of it.

    As I wrote earlier, it’s a “cult for hire” that will slavishly adopt whatever beliefs are spoon-fed to it by the so-called “right wing media”, which was created over the last few decades to serve exactly such purposes.

    All the fossil fuel corporations had to do was to plug their particular message into the machine, and bingo: a “grassroots denial movement” springs up. The content doesn’t even matter. If they had plugged in “Pepsi is better than Coke”, the same trolls would be posting that on the world’s blogs instead of denying global warming.

  17. 67
    Retrograde Orbit says:

    Don’t daemonize your opponents. That is never conducive to finding solutions.
    The fossil fuel industry is not a faceless devil. There are people in charge there. People who have children and grandchildren. Why would they not be concerned about the future of the planet?
    Inhofe doesn’t read from a script, he actually believes what he says – unimaginable as that may be.
    FOX news doesn’t just broadcast what is being plugged in. They broadcast what their listeners want to hear (ratings you know). That’s why the listeners tuned in to begin with. “Pepsi is better than Coke’ would not do that, but there is a desire to hear ‘global warming is a hoax’.
    I might just dismiss that as ‘delusional thinking’. Maybe another sign of the decay of society that I see all around me? Be that as it may …
    The key problem is that global warming is not intuitive. Global warming denial however is. And so it is hard to find common sense arguments to support global warming, but very easy to find (bogus) common sense arguments against it.
    There was a time when everybody thought the earth was flat. Somebody with a theory that the earth was round would have been laughed out of town. Can’t you see? It’s flat!

  18. 68
    Mal Adapted says:

    Inhofe doesn’t read from a script, he actually believes what he says – unimaginable as that may be.

    While sincerity stupidity is usually the least hypothesis, in Inhofe’s case there is ample support for an inference of malice. What is your evidence that he actually believes what he says?

    The key problem is that global warming is not intuitive. Global warming denial however is. And so it is hard to find common sense arguments to support global warming, but very easy to find (bogus) common sense arguments against it.

    The question is whether and to what extent “common sense” is conditioned by the documented campaign, by named, obviously self-interested individuals and groups, to manipulate public opinion in their favor. I’m utterly convinced that the denier disinformation campaign is real and pernicious, but I’m not willing to ignore the fundamental agency of my family, friends, and neighbors. Surely they all have the same ability, and the responsibility, to accept reality that I do. For me to think I’m somehow special would be arrogance!

  19. 69
    Ray Ladbury says:

    Mal Adapted et al.,
    OK, let us say you come across someone who is politically conservative. Do you assume they are climate denialists? And even if you subsequently learn your conservative acquaintance is in denial about climate, how does that help you? How do you act on that information? Conservatives–as well as liberals–may have a variety of reasons for their denial.

    Some simply do so because that is the default position at present for their tribe, and conservatives have a tendency to be agreeable within the tribe to preserve social harmony. Some reject climate change because “Al Gore is fat!!!!!” (Argumentum Al Gore). Some reject climate change because the consequences could be severe and they simply don’t know what to do about it. (Argument from consequences.)

    This shouldn’t be a left-right issue. It is not in most of the world.

  20. 70
    Patrick 027 says:

    The key problem is that global warming is not intuitive. Global warming denial however is. And so it is hard to find common sense arguments to support global warming, but very easy to find (bogus) common sense arguments against it.

    At a time when it was (widely ? or maybe most people just never thought about it) believed that a net force was necessary to sustain motion (rather than to accelerate it), sure, …

    … but anybody familiar with conservation laws (and while we do have inflation and such, the idea of a budget should help economists and others in that), must realize what goes in must come out or gets stored. Light is energy. Heat is energy. Blankets keep your skin warm on a cold winter’s night. CO2 makes the air more opaque to ‘heat rays’; over a band with variation so it’s only saturated in parts (tropopause level). 2nd law + LTE => (emissivity toward = absorptivity from (monochromatic, polarization and direction if necessary) (okay, that one requires some more education, but wouldn’t a lot of people accept it without specifying LTE and knowing what that means?). Snow is bright (well, when fresh). Air cools when depressurized, so convection can only do so much; not much air in space… Feedbacks spatially, temporally variant; affects circulation, precip. We need water, fresh water. Crops depend on weather. We need food. We like food, esp. chocolate, maple syrup, tomato sauce, cheese,…(well, I do). Cold weather kills a number of nasty venomous creatures. Ecological disruptions can lead to plagues. Ecological succession takes time; big trees are usually old, lichens don’t grow fast(right?); except for extinction, evolution tends to be slow. To paraphrase an article I once read in Scientific American (?), ‘winter is our best/most effective public health program’ (okay, I get that one’s not so intuitive, but it makes some sense). What’s so hard? Originally, the hard part was believing humans could be such a powerful ‘force’, but shouldn’t we have gotten past that by now?

    There was a time when everybody thought the earth was flat. Somebody with a theory that the earth was round would have been laughed out of town. Can’t you see? It’s flat!

    Flat enough for travelling around the village. Eratosthenes actually calculated the size of the Earth based on shadows.

    (re my 65 “evolution. Rockeffeler seemed to embrace it (that’s the impression I got) (though did he understand it? ” … well, did vertical monopolies come into being before endosymbionts were discovered? If so, kudos to the robber barrons. But that brings us back to the evolution of land plants and the carbon cycle. :) )

    [Response: Can we stick to the topic of the post? There is an open thread for everything else. Thanks - gavin]

  21. 71
    Patrick 027 says:

    re 69 Ray Ladbury – okay; see Sean’s statement about US vs world (on that note, I forgot to mention Soviet Lysenkoism and Mao’s distaste for Malthus and his apparent belief that manpower was the only limiting factor in food production (perhaps a slight caricature – he did realize that you need to fertilize the ground with clay pots :( ) (also related to views of some libertarians? – ‘no limits to growth’)… and as for what I said earlier (the expectation of a pro-small government correlation), counterpoint: there are examples of people holding beliefs or for that matter, policy positions counter to their stated values or overall attitudes, or at least, what one might expect those values or attitudes to be (based on party branding or…). (Also, there is the category of far-right big gov.) But listing those examples would be just way too off-topic; just watch the Daily Show, Colbert Report.

  22. 72
    Patrick 027 says:

    Sorry Gavin.

  23. 73
    CM says:

    On topic: In the OP, Gavin writes:

    The error bars cover the ‘likely’ range (33-66%), so are close to being ±1 standard deviation [...]. [...T]he ‘ANT’ row [...] is around 0.7 ± 0.1ºC, and the OBS are 0.65 ± 0.06ºC. If you work that through (assuming normal distributions [...]), it implies that the probability of the ANT trend being less than half the OBS trend is less than 0.02% – much less than the stated 5% level. The difference is that the less confident statement also takes into account structural uncertainties about the methodology, models and data.

    Wow! Now, about those error bars, the AR5 attribution chapter says:

    We moderate our likelihood assessment and report likely ranges rather than the very likely ranges directly implied by these studies in order to account for residual sources of uncertainty including sensitivity to EOF truncation and analysis. (final draft, ch. 10 p. 19)

    Do I understand correctly that the quantitative likelihood derived from the attribution studies (Jones et al, Gillett et al) has been downgraded twice by expert judgment to form the AR5 “95%” assessed likelihood?

    That is, first, by taking a 90% uncertainty range on the attributable trend as a 66% range; and second, as noted by Gavin, by upping the possibility of humans accounting for less than half the warming to 5% from the 0.02% suggested by the (already downgraded) uncertainty bars?

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