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Filed under: — eric @ 1 November 2006

There has been an interesting exchange of letters in the Forum section of the American Geophysical Union’s weekly newspaper, EOS. Last year, the American Association of Petroleum Geologists (AAPG) took the remarkable step of giving a fiction writer, Michael Crichton, its journalism award. Representatives of the American Quaternary Association (AMQUA )1 took offense and wrote a letter to EOS about it. Then Fred Singer and Kevin Corbett wrote to AGU to complain about AMQUA’s letter.

Singer claims to be defending the AAPG, though it is by no means clear that the official position of AAPG is representative of its members (see the discussion on AAPG’s website, here (Note: subsequent to this article, these pages were put back into the members-only area)). For his part, Corbett accused the American Geophysical Union of “trenchant advocacy for a preferred political agenda.” We think that AGU’s official response was right on the mark: “AGU does not have any agenda in this arena beyond ensuring that the best available science is used in making public policy.” You can read the complete letters, and AGU’s response, here.

In further response to Singer’s letter, we (and the AMQUA folks) are certainly aware of the evidence for the so-called “1500-year cycle” in climate. But we are unaware of any evidence that this has anything to do with the current warming, as Singer claims. And we find it is curious that Singer’s recent view that the earth is cooling has been replaced with the view that the current warming is “unstoppable.”2

It also worth pointing out something in Corbett’s letter that AGU neglected to mention (no doubt because they were being polite). In trying to make the point that the “anthropogenic hypothesis” (that humans are influencing climate) is controversial, Corbett cites a recent EOS article. In that article,3 Wally Broecker and Thomas Stocker contest the idea that humans began significantly influencing atmospheric carbon dioxide concentrations thousands of years ago. But nowhere do Broecker and Stocker ever question that humans are the chief cause of rising CO2 since the industrial era began (i.e. around 1850).

Wally Broecker is one of the world’s most respected climate scientists. Citing one of his papers (or anyone’s paper) as if it made a point that it most certainly did not — and with which Broecker would disagree completely — is poor scientific practice, and is very misleading, at best. We suggest that Mr. Corbett be a little more careful with such things if he wishes to be taken seriously.

1The Quaternary refers to the last ~2 millions years of earth history, during which the great ice ages have occurred.
2Singer, S. F. and D. T. Avery (2006), Unstoppable Global Warming: Every 1500 Years, 260 pp., Rowman and Littlefield, Lanham, Md.
3Broecker, W. S., and T. F. Stocker (2006), The Holocene CO2 rise: Anthropogenic or natural?, Eos Trans. AGU 87(3), 27.

67 Responses to “AGU, AAPG and AMQUA”

  1. 1
    Eli Rabett says:

    There was an additional item on the front page of the EOS issue setting forth the AGU policy on taking public positions: (behind the wall)

    “AGU has not and will not articulate or support any public position on issues that extend beyond the range of available geophysical data or recognized norms of legitimate scientific debate. Positions of AGU must be based on sound science. Members are notified when the Union is preparing a position and have an opportunity to provide input. Accepted positions are publicly available. Each has a sunset limit; all must be reviewed on a regular basis. You can read the full Union policy on advocacy at http://

    However, I think you missed the major point of Singer’s letter. He is opening a new front in the climate wars, the 1500 year climate cycle. As I noted yesterday the book is already out and if you Google it, you will find that every right wing web site is hailing this as the answer. Of course, what the question is remains open.

    I suppose one must read the book to start answering the inevitable. It might be good to get ahead of the curve.

    [Response: Thanks for adding these points. See my response re 1500-year cycle, below comment 6. -eric]

  2. 2
    Manboy says:

    “And we find it is curious that Singer’s recent view that the earth is cooling has been replaced with the view that the current warming is “unstoppable.””

    I’ve been looking at the comments of some of these skeptics. I’ve come under the impression that there aren’t very many skeptics whose skepticism stood the light of day. What I’m wondering at the most is why do these people continue to be listened to ? The way I see it they’re contributing nothing to the discussion on global warming, only hindering it by their unsound claims.

    Didn’t Singer used to be of the opinion that CFCs and ozone depletion are unrelated ? Why do people continue to listen to him ?

  3. 3

    Global tempertures have slipped sideways since 1998 as part of a coherent global climate signal. They will continue to shift sideways and trend downwards over the next few decades – as in the trend seen between 1946 and 1975.
    Some of the conections between the IPO and climate are emerging from Australian hydrological analysis.
    Some interesting aspects of this can be seen at:
    – there is a recording of a presentation

    [Response:A nice thing about confident predictions like this (which aren’t made in the cited abstract by the way!) is that we can wait and see what happens. I’m not holding my breath. -eric]

  4. 4

    I do think the impact that Michael Crichton has is quite extraordinary. “State of Fear” provides a totally misleading scientific commentary on global warming; yet, some of my friends and colleagues believe it! I don’t think I have ever been so motivated to write a rebuttal to anything – and so wrote a 6,500 essay against “State of Fear” (& some of his other work) over my summer holiday.

    “libenter homines id quod volunt credunt”
    (men willingly believe that which they wish for) Caesar

  5. 5
    pete best says:

    Fred Pearce gives a whole chapter on the 1500 year cycle in a book on climate change released recently. No mention of Singer in it but two other people who seemed to have found some sort of 1500 year cycle linked to strong solar activity, Gerard Bond being the person who up until recently has don the most work in this area.

    [Response:See my comment after #6, below. -eric]

  6. 6
    Grant says:

    … we (and the AMQUA folks) are certainly aware of the evidence for the so-called “1500-year cycle” in climate.

    Unfortunately, I’m not aware of the evidence. Do you have a link to papers on the topic? What, in your opinion, is the strength of the evidence?

    [Response: As Eli pointed out (comment #2 above), we probably need to do an entire post on this. But I’ll give a bit of background here.

    Many records of past climate that stretch back 100,000 years or so — notably ice cores, but also some marine sediments, lake sediments, etc. — show very distinct evidence of what is typically called “millennial-scale variabilty”. That is, variations in climate proxies that seem relatively large in magnitude, on timescales of 1000 years or so; arguably larger than might be expected from observed climate (we have only been watching it a bit more than 100 years). In some records, particularly those from the North Atlantic Region, but also in some other regions, the magnitude of this millennial-scale variabilty is much greater during the last glacial period — around 11,000 to 90,000 years ago — than it is during the most recent warm period, the Holocene (the last 11,000 years). The clearest example of this is the record of oxygen isotope ratios in the GISP2 ice core. GISP2 was one of the two deep ice cores (the other was GRIP) drilled in central Greenland, completed in 1992. It is characterized by very good dating (we know the age of the ice extremely well at each level). GISP2 is also characterized by very distinctive, abrupt increases in oxygen isotope ratios — and we know from other, independent evidence that these are abrupt warming events. They are followed by periods of warmth, and then cooling, also abrupt sometimes. See the figure here for example, and note how much greater the variability is in the earlier part of the record that in it in the Holocene. The Vostok ice core from Antarctica is also shown in the figure. It also seems to show more variabilty in the glacial that in the Holocene, but the difference is not nearly so great, and neither the warmings nor the coolings are abrupt as they are in Greenland. In any case, the spacing of the warmings and coolings in both these records occurs on a millennial timescale. This is most easily seen in the GISP2 record, where the spacing between the obvious abrupt warming events is typically 1500 years. In fact, a spectral analysis of the record shows a very distinct period of 1500 years, that it statistically significant by most standard measures of probability. In other words, there is a “cycle” in this record. The “cycle” is not statistically significant in any other record, including in other Greenland ice cores. Nor does it appear in the Holocene in GISP2. So the case that it is a “cycle” is somewhat weak. Clearly, Singer is aware of this, which is why in his letter he writes “roughly 1500 years”. But the important point is simply that these records show variabilty on timescales of millennia, and that variability seems rather large, at least prior to 11,000 years ago.

    Now, it is clear from these records that climate can vary quite a bit without any input from humans. And it is tempting to attribute the ice core observations to some “cause”, such a solar variabilty, as Gerard Bond did in an oft-cited paper in Science. Another standard explanation (which probably has a lot more merit) is variations in the strength of the meridional overturning circulation. It is also tempting to attribute recent variations — e.g. the “Little Ice Age” to the same cause(s). And Singer would like, then, to attribute the current warming to the same thing(s). The problems with leaping from the GISP2 ice core to the current climate are many, and I’ll just name a few. First and foremost, one would need some evidence that the purported causes are going in the right direction. If the natural cause is solar variabilty, then you have the immediate problem that the sun isn’t changing measureably now. If the cause is changes in North Atlantic meridional overturning circulation, then you need evidence it is changing in the right direction. Second, one would have to explain away the forcing due to CO2. That is, if you are going to attribute the current warming to “all natural causes”, you are going to have to explain why the CO2 increase is not contributing. That’s going to be rather difficult, since it is
    very very well established physics. Third, you are going to have to explain why the entire planet (not just the North Atlantic region) is warming, which was not the case during the observed “1500-year” variations of the past.

    I hope this helps a bit. It is clear we’ll need a more complete post on this at some point. –eric

  7. 7
    Timothy says:

    #3 – I think you are wrong. 1998 was an exceptionally warm year because of the strong El-Nino. If you look back at the Hadley/CRU temperature record you can see that a similar thing happened to global temperatures after the 1983 El-Nino, which wasn’t exceeded until 1990.

    What’s striking is that there hasn’t been a year cooler than 1983 since 1996. In 5-10 years time we will probably rarely see any years cooler than 1998 [unless there’s a decent-sized volcano].

  8. 8
    Joel Shore says:

    Re #3: Temperatures have not “slipped sideways” since 1998. They have continued to rise. This claim that the temperatures have not risen seems to be based on the fact that, according to some measurements, 1998 is still the warmest year on record (with 2005 a close 2nd)…while other compilations show 2005 slightly surpassing 1998. However, using this data to claim that there has been no warming since 1998 is silly, as any sort of running average over a few years continues to show warming. In fact, the 1998 peak was a huge outlier at the time it occurred and even the data sets that show it still as the warmest year have 2002 through 2005 in the spots of the 2nd through 5th spots. So, what the data in fact show is that in just the 7 years between 1998 to 2005, a temperature that had been a huge outlier at the time it occurred is now barely higher than what has been the mean temperature for the last few years. This is in fact evidence that warming continues quite rapidly.

    Here, in Rochester, we will often get a few anomalous days of warm temperatures (say, highs of 70 or more) in early April and then a cool down with such temperatures not seen again until well into May. By the sort of logic that people are using to claim that there has been no warming since 1998, we Rochesterians would conclude during that period in mid and late April that we were not heading toward summer but in fact cooling back toward winter. Needless to say, such a conclusion would not be correct.

    [Response: Obviously, claiming that global warming has stopped since 1998 (a year with temperatures above the long-term trend line) is as ridiculous as claiming that global warming has hugely accelerated since 1999 (a year below the long-term trend line). I wonder why I only hear public claims of the former (including repeatedly by Richard Lindzen)? -stefan

  9. 9
    Joel Shore says:

    Re: #2 “Didn’t Singer used to be of the opinion that CFCs and ozone depletion are unrelated ? ”

    Actually, as far as I know, your past tense isn’t even justified here. I.e., I believe that Singer continues to this day to deny that connection (or at least to argue that it is insignificant). Of course, if anyone has evidence that Singer has in fact accepted the well-established scientific consensus on CFCs and ozone depletion, I will be happy to stand corrected.

  10. 10
    Steve Sadlov says:

    Much of the “voice” of North American climate change perception is colored by the fact that most of the media and population still remain concentrated in the Eastern third of the country, where there has been a REGIONAL anomaly of some fairly wimpy winters and hot and muggy summers. Meanwhile, here out West, it’s been cool, overall, since the mid 1990s.

  11. 11
  12. 12
    Dennis Avery says:

    As the co-author of Unstoppable Global Warming Every 1500 Years, I want to correct your account of the Eos-Forum exchange. Fred Singer supported climate cooling 10 years ago when the satellite data showed climate cooling. Since then, the data changed and so did his opinion.

    Similarly, until 1988, published measurements showed no increasing trend in stratospheric chlorine, indicating that natural sources of chlorine were more important than those from CFCs [1]. Singer changed his opinion when published data changed in 1991, which happened four years after the Montreal Protocol was signed [2].
    1. See S.F. Singer. Ozone Depletion Theory. Science 261, 1101-1102. 1993.
    2. C.P. Rinsland et al. J. Geophys. Res. 96, 15523 (1991).

    [Response: Thanks. But the record indicates otherwise. In 2000, Singer is quoted as saying ‘Certainly it has not been warming’, and even in 2005: ‘warming, such as it is, is extremely slight’. Now, a year later it’s unstoppable? There’s been new evidence, but none that would support such a radical 180 degree shift in position. -gavin]

    [Response: Furthermore, on the CFC-ozone link, Singer stated as late as 1995: ‘The facts are that the scientific underpinnings are quite shaky: the data are suspect; the statistical analyses are faulty; and the theory has not been validated’ – Hardly a ringing endorsement of the science. – gavin]

  13. 13
    cbone says:

    Re: 3 Richard Linzen made a similar assertion in the Telegraph:

    For the past five years, the global mean temperature has been flat to within a few hundredths of a degree (well within the measurement uncertainty); indeed, there has been no statistically significant change in 10 years.

  14. 14
    Joel Shore says:

    Re #12: While Singer may have changed his tune regarding whether or not CFCs and such were increasing the amount of stratospheric chlorine, his website on ozone shows that he continues to question the significance of this fact…Or else he hasn’t bothered to keep his website up-to-date. (See … search on ozone and read, for example, his “Five Scientific Questions on the CFC-Ozone Issue” page.)

    He also seems to make the strange argument there that it was still wrong to have entered into the Montreal Protocol in 1987 because the scientific evidence that stratospheric chlorine was rising hadn’t conclusively been shown by then, even while admitting that the evidence did eventually support this. So, I think this gives us a good idea of how Singer operates: Deny the accumulating evidence until it becomes utterly ludicrous to do so. Then continue to argue against policies of mitigation on the basis of other arguments and continue to criticize those who were convinced by the mounting evidence much sooner than he was.

    [Response:In response this and a few other comments here, I think it is important not to attack Singer merely for disagreeing with the mainstream view. Healthy skeptism is a good think in science, and we really can’t fault Singer for no jumping on everyone else’s band wagon. I very much dislike the term “accumulating evidence”, though we see it all the time in Nature, Science, and other top journals. It is silly, beause it is the already-accumulated evidence that it is important, not what might accumulate in the future. The problem with Singer is not that he doesn’t agree with everyone else. The problem is that he creates his own bandwagons — a new one every few years, it would seem — based on not very good evidence, and then complains loudly when the rest of us don’t jump on them. -eric]

  15. 15
    Steve Latham says:

    Wikipedia’s Fred Singer page says it is in need of review:
    I find it interesting that he also denies/denied UVB links to skin cancer and 2nd hand smoke to lung cancer.

  16. 16
    Steve Latham says:

    Re #10
    I don’t think you can authoritatively speak for “out west”. In British Columbia we’ve got a lot of trouble with shrinking glaciers, warming rivers (a related issue), and forest pest outbreaks due to increased temperatures. Some similar issues have been noted in Washington, Oregon, and parts of Idaho and Montana (and it’s been worse since the mid-90’s). Maybe your definition of “out west” is different than mine.

  17. 17

    The CRU has 2005 as equal second and other data sources marginally differ. All I said was that the global mean average temps ‘slipped sideways’ since 1998.

    No one (or at least not me)is saying that it is ‘all natural’. What I did say was that temperatures will continue to slide over a couple of decades in the same way, and for the same reason, as temperatures between 1946 and 1975.

    There is a pattern of Pacific Ocean sea surface temperature changes found in direct measurement, biology across the Pacific, sediments, tree rings – a mountain of evidence.

    The ‘confident prediction’ is hardly long term but it is based on long term trends. That the 1998 to 2006 temperature trend line continues to diverge markedly from the 1975 to 1998 trend line of 0.2 degrees C per decade. As far as the literature is concerned, there are people all over the world saying that a ‘cool phase’ of the IPO ‘may’ be happening since 1998. Such caution is appropriate for science – but there is an inevitable logic about a bipolar multi decadal phenomenon shifting phase every couple of decades. A great deal of science has been done but the implications may not be widely apparent as yet. As a trained Environmental Scientist (in the applied cross-disciplinary sense)- my intention is to foster cross disciplinary communication on an important area of climate science – not to prove an obscure and irrelevant point.

    The connections between the IPO and global climate start to emerge from Australian hydrological analysis (which was part of the presentation linked to – which then went on to discuss some implications through modeling and a preliminary finding of independence from ENSO). The phenomenon involves decades long term modulation of the both the frequency and and intensity of El Nino and La Nina. Cool phases bring more intense and frequent La Nina. Warm phases bring more intense and frequent El Nino.

    The connection between El Nino and global temperatures seems too simple to require much discussion from me – but it is widely discussed elsewhere.

  18. 18
    Joel Shore says:

    Re #17 (Robert Ellison): Regardless of your own hypothesis on how global temperatures have and will behave, my argument is that your statement about the temperature since 1998 is not supported by the data…or if so, only in the trivial sense of comparing two one-year periods several years apart, which is not the right way to deal with data that has fluctuations!

    Let me give you a concrete example: If you look at the CRU data set here you could also conclude using your same logic, for example, that temperatures “slipped sideways” (or even fell) between 1983 and a year in the range of 1987 – 1989, and between 1990 and years in the range of 1994 and 1996. You can even define periods in there where it looked like temperatures were falling. Do you believe that these are real and that the temperature in those intervals was actually slipping sideways in any real sustained trend? How does that fit into your hypothesis?

    My point is that by taking an anomalously-high year as the starting point (and 1998 is a doozy in that regard!), you are likely not to find the temperature equal to or exceeding that value for several more years. However, all the available evidence from the temperature record indicates to me that the temperature is continuing to rise, as some sort of noise-reduction method such as a running average of temperatures over (say) a 5-year period shows. Admittedly, because global temperature is a fluctuating quantity, it is hard to say with certainty what the trend has been over a short recent time period. However, there is certainly nothing that I see in the recent trends that are incompatible with a continued steady rise in the average global temperature, with of course, fluctuations imposed upon it as there always are.

  19. 19

    The recent temperatures are merely consistent with broader trends. Many people have suggested that a cool phase of the PDO/IPO ‘may’ have commenced in 1998. Caution is admirable in science but there is an inevitable logic to a phase change in a bipolar multi decadal phenomenon occuring every few decades.

    Global temperatures of the 20th century showed a warming phase to the 1940�s, a cooling phase to the 1970�s and renewed warming to 1998.

    In the past century ‘cool’ (as in sea surface temperatures) PDO regimes prevailed from 1890-1924 and again from 1947 to 1976, while ‘warm’ PDO regimes dominated from 1925 to 1946 and from 1977 to 1998.’

    The records are consistent over the 20th century.

    I must admit, however, that I was beginning to doubt my own sanity and put the question to an unnamed source at the University of Newcastle – Australia.

    “The history of the 20th century global climate, is a warming (PDO+) epoch 1910-1945 where El Nino were more frequent, followed by a cooling (PDO-) epoch where La Nina events dominated. Since 1975 weâ��ve returned to a warming (PDO+) epoch where once again El Ninos are dominant.”

    Interannual variations are not relevant – merely the trends seen within the theoretically consistent framework of the PDO/IPO and associated long term modulation of both the frequency and intensity of La Nina and El Nino.

    Instead of being unflectively critical – look at the evidence. Understand the Australian hydrology – some of which is included in the link provided previously.

    I may be wrong and I may be crazy – but I may just be the lunatic you’re looking for.


    [Response:Robert, this comment of yours got caught in our “moderation queue”. Not sure why! In any case, I have approved it.

    Regarding your comments on the IPO/PDO, the problem is that you are implying predictability that just isn’t there. I don’t think you’re crazy — you’re just just jumping to conclusions most of the community of scientists wouldn’t jump to. As I’ve said before, we probably need to have a post on the use and abuse of the PDO. Like the AMO, it is not really an oscillation, in the way that El Nino is, and is hence inherently unpredictable. I refer you to the papers by Clara Deser of NCAR on this subject, notably this one: -eric]

  20. 20
    Pat Neuman says:

    re: Lindzen’s assertion (#13.)

    Using uploaded global land_ocean data in a spread sheet, the difference between the 1995-2004 average (0.459 deg C) of annual
    global temperature anomalies and the 1996-2005 average (0.435 deg C)
    is 0.024 deg C, indicating a rate of global surface temperature warming of 2.4 deg C on a 100 year basis.

    Also see:

  21. 21
    Bryan Sralla says:

    Who gave you the key to get into the AAPG “Members Only” comments? It seems we have a disgrunted AAPG member amongst our ranks.

    As everyone can now see, we geologists are not really the contrarians we have been made out to be. Yes, it is true that the AAPG policy position is embarassing. There, I said it. It hurts though, as our organization is one of the premeir geological organizations in the world, and its members have analyzed more sedimetary rock data than any other group on the planet, by far.

    [Response: The comments are linked from the AAPG home page. No disgruntled members required (though it appears it wouldn’t have been hard to find one). -gavin]

  22. 22
    Mark A. York says:

    Peter Winters that’s good essay on Crichton. I tried to leave comment after registering but Mark Lynas’s site is squirrelly and I get an error page every time.

    I wrote a whole novel using the correct information he skewed and made mockery of in State of Fear. So far the agents in New York haven’t been kind to the concept. If they bought lies as fiction they should in turn buy truth in fiction which Hemingway called the “hardest thing: to make something truer than true.” I think I’ve done that with “Warm front.”

  23. 23

    Thanks Eric – my last post on this topic here. I look forward to a new posting on the PDO/IPO. You have my email – I could shoot you some relevant peer reviewed papers on the Australian hydrology I mentioned.

    The abstract in the link is still talking about interannual persistence?

    There doesn’t seem much dispute in the science community about the PDO/IPO as a multi decadal phenomenon? It is, after all, discussed in the IPCC assessment and the Arctic Climate Impact Assessment Report. What I feel has changed is the recent insights into long term modulation of both the frequency and intensity of EL Nino and La Nina during warm and cool phases of the PDO/IPO.

    The PDO was named by Stephen Hare (from memory) – and he was talking about periodic flucuations, in salmon originally, in Alaskan fisheries.

    While the onset of a phase change is not predictable (while the cause remains unknown) – phase changes can and have been identified after the event. The PDO index is by no means definitive after 1998 but ‘predicting’ a ‘cool phase’ is like predicting that it will rain sometime in the future – good odds unless the planet has moved so much that a long lived property of global climate no longer applies – then all bets are off and we really are, to use an Australian expression, up Shit Creek.

    I am sure that there will be many people closing following the PDO/IPO indices, as well as global temperatures, over the coming years.

  24. 24

    Re: Eric’s response to #6

    If you are going to attribute the current warming to only GHGs, you are going to have to explain, how the increase in solar forcing in the first half of the 20th century, could have equilibrated so quickly, when the climate commitment papers, say it takes several decades for most of surface temperature to equilibrate, and sea level rises for a millenia or more. Some of that 0.8W/m^2 of heat storage (Hansen 2005) that is being annually stored in the ocean must be due to the increase to the current plateau of solar activity. Further increase in solar activity in the latter half of the 20th century is not needed.

    On the issue of the 1500 year cycle, you might be interested in the proposal that it is the superposition of the the Gleisberg and Suess cycles:

    Holger Braun, et al, “Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model” Nature 438, 208-211 (10 November 2005)

    While the Gleisberg and Suess cycles are detected in the interglacials, their superposition, as you noted, is only apparent in certain glacial records. A possible explanation, is that the threshold for some minor climate mode is reached by this superposition in the ice age climate, but that mode is not present in the interglacial climate, or the threshold for that mode is different or not reached.

    [Response: As a co-author on the paper you cite above (and other papers related to the 1470-year cycle), I should perhaps add that in my view these cycles have nothing to do whatsoever with the recent global warming – and I don’t know any scientist working on these cycles who disagrees. Note that in our model simulations the temperature changes seen in Greenland, Antarctica and elsewhere agree quite well with data, and are caused entirely by changes in ocean heat transport which has almost no impact on global mean temperature. This is something entirely different from the widespread global warming that is happening right now. -stefan]

    [Response: Stefan’s point is very important. The mechansism proposed in Braun et al. is one of amplification of solar forcing by a particular mechansism, one that distributes heat around the globe, not one that leads to significantly warmer global temperatures. This is similar to the debate about the Little Ice Age. For a long time, people thought it was a globel signal — that is, cooling everywhere at the same time. We no longer think that, because the data show otherwise. We don’t think this for the longer term warmings and coolings in the Antarctic and Greenland records either. This was suggested in theory at least back in 1992 in two independent papers by Stocker and by Crowley. The data show it very clearly in Blunier and Brook, 2000, in Science. We’re not saying that there is not significant climate variabilty on timescales of 1500 years. There is! What we are saying is that it doesn’t result in a significant global mean temperature change. Neither the data, nor the physical mechanisms underlying the data, would lead to any other conclusion.

    Finally, I would like to emphasize that everyone in the scientific community understands and accepts that even some of the 20th century warming is due to natural changes. Most of the research on the subject is aimed at figuring out such details, and the results are well known, and have been for some time. [I never said it had to do onlywith Greenhouse gases.] What we’re objecting to is the cavalier approach of simply declaring it is “due to the 1500 year cycle.” That’s what Singer did in his letter, and does in his book. –eric]

  25. 25
    Urs Neu says:

    Re 24

    The problem with your argument is, that the climate commitment (delayed warming) of a forcing that stops in 1950 would be mainly felt during the immediately following decades and then flatten strongly. I.e. there would be further warming mainly in the 50ies and 60ies and less in the 70ies, and only a very slight warming afterwards (see e.g. Wigley 2005). However, what we see in reality is the opposite: slight cooling in the 50ies and 60ies and strong warming afterwards.
    This inevitably points to the fact that there must be other and stronger forcings effective during these times.

    According to what Hansen 2005 (Science) and Wigley 2005 (Science) present, and considering the possible solar forcing compared to the assumed GHG forcing in the models, it is very unlikely that the commitment to the solar activity increase before 1950 is contributing more than a few hundredths of a degree after 1970, which is less than 10% of the observed increase.

  26. 26

    Stefan, Do you have an estimate of where we are in the Gleisberg and Suess cycles and therefore what their superposition is? Since we don’t have a good model of what explanatory power these cycles have for levels of solar activity, I too would not attribute global warming to them, although I also don’t see the evidence for arguing that “these cycles have nothing to do whatsoever with the recent warming”. It is pretty clear that we there is a lot we don’t know about solar activity. Sunspot models currently account for only about 80% of solar variation over the last two cycles, during a period when solar activity has not greatly changed from its 1940 levels reached earlier in the century. The models cannot be considered validated outside this regime yet. With solar activity currently (per Solanki) at one of its highest levels in the last 8000 years, and less than 8% likely to maintain this level for another 50 years, one is not entitled to assume that high levels of solar activity over this period of recent warming is a mere unrelated coincidence. In addition, the solar conveyor theorists, based on a slowing of the solar conveyor this last (11 year) cycle are hypothesizing that the second cycle out will see much reduced solar activity. The activity of the next cycle is expected to continue to be high. Since solar activity, by climate commitment studies of the equilibrium time of the climate, must explain some of the recent warming, it would be a lot cleaner result, if the Suess and Gleisberg cycles were somehow aligning with this recent solar activity, and thus providing some insight and hope for predictability. It is nice in science when disparate things come together and start to make sense. Unfortunately for this type of longer term phenomena, we may not live long enough to see the resolution, if it isn’t coming together now. Even though I am probably older than you, I still have hopes of seeing at least the next two cycles, and perhaps some advancement of knowledge in this area.

  27. 27
    John L. McCormick says:

    RE # 2 and the topic of this thread;

    The commenter said [I’ve been looking at the comments of some of these skeptics. I’ve come under the impression that there aren’t very many skeptics whose skepticism stood the light of day. What I’m wondering at the most is why do these people continue to be listened to? The way I see it they’re contributing nothing to the discussion on global warming, only hindering it by their unsound claims. ]

    My reply: Sceptics are listened to (worse yet, acknowledged that their opinion has value) because we feel an obligation to refute their nonsense, discredit them, prove them wrong and win back the argument before a dumbfounded average reader/audience.

    These aging shills are never going to stop their gaming the discussion and goading the legitimate science community and people of common sense to turn attention to them as if they are relevant.

    The past several years of US climate change discussion and argument have been shaped, in large part, by the Bush machine, corporate vested interests shoveling money to Sen. Inhofe, CEI, CATO and the award-winning scholar Michael Crichton. Name your favorite contrarians here………… Bottom line, these are irrelevant beings we recognize as moving forces to be confronted. We get to throw the food back at them and they return the volley. Then, we scoop our plates and heave another round. If you think that is a mischaracterization of what is going on, spend some time trolling the blogs and see for yourself; attack then counterattack then new attack and new counterattack……serious climate change discussion does Rush Limbaugh.

    No wonder the public turns off the chatter and goes back to BAU.

    I urge RealClimate sponsors and contributors to see how pointless and time-consuming are these verbal jousts fortified by code and obscure reports and journal articles.

    Does anyone believe the average reader will run to the library to research Fred Singer’s latest zinger? They take more from news articles that describe the plight of Midwest farmers suffering continuing drought or severe water restrictions in the UK. That is the news they can process even if it does not cause them to retrofit their home with energy efficient appliances (wish I had the cash to do that myself).

    Two recent articles that are far more relevant than the EOS letter (in my opinion):

    Drought-Hit Australia Battles Climate Change linked at:

    [ SYDNEY – Australia is already feeling the heat from climate change with a five-year drought devastating rural life, severe early season wildfires and record unseasonal temperatures.

    Every four days, a farmer commits suicide under the stress of failing crops, dying livestock and debt as the worst drought in 100 years bites deep into the nation’s psyche and erodes economic growth. “The current drought highlights how vulnerable we are to climate change,” said farmer Mark Wootton. “We will never solve the drought if we don’t solve climate change.” ]

    In the article the view of the Australian Bureau of Meteorology provided a much more worthy topic for RealClimate when it said Australia and the globe are experiencing rapid climate change.

    Are we witnessing the disintegration of slow motion?

    Then read:

    China Turns to Saltwater To End Drought

    [“China is expected to desalinate 800,000 to 1 million cubic metres of sea water per day and use 55 billion cubic metres annually by 2010,” the State Development and Reform Commission said, detailing China’s ninth five-year plan.

    China desalinated 120,000 cubic metres of sea water per day last year.

    It was not immediately clear how China, which is also desperately short of fuel, would power the energy-hungry desalination plantsâ??. ]

    Frankly, what is relevant in some wing nut saying warming is cyclical and comes around about every 1500 years. Great topic for dissertationsâ?¦.useless for Australian and Chinese municipal water supply agencies. They are capitalizing billions of dollars to manufacture fresh water because they cannot bet on the rain coming in time.

    I have asked the question to RealClimate before and I ask again:

    Would we recognize abrupt climate change if it hit us in the face or do we first have to see it on a computer screen?

    Time is running out. Put the food down and tell us what you scientists really believe. I sometimes wonder if scientists can.

  28. 28
    Eli Rabett says:

    I suspect that AAPG is somewhat like ACS, with lots of members, but controlled to a large extent by the underlying industry. We get bennies, but you know what drives the agenda.

  29. 29
    Grant says:

    Re: #26 and the ongoing “debate”

    I too am frustrated that the well-funded, pervasive efforts of contrarians are shaping the public debate.

    But the efforts of RealClimate are not in vain. Far from it. For example, a recent post regurgitated some of the same old same old contrarian garbage. But the RC moderators didn’t need to refute it; several “regulars” did the job quite neatly. And, they did it without ad hominem, without SHOUTING, instead applying cool-headed logic including references to the scientific literature.

    Perhaps RealClimate is creating an “army” of well-informed advocates, schooled in sound climate science and well-rehearsed in civilized debate: exactly the kind of arguments that actually *persuade* the undecided. Yes, there are plenty of blogs with *claim/counterclaim/reclaim with insult/recounter with even more stinging insult*, etc. But I have also seen blogs with *ridiculous claim/factual refutation/reclaim with insults/won’t sink to that level*. This is far less satisfying for the blog poster (you don’t get to visibly “win” the debate) but *far more persuasive* to the undecided reader.

    I agree that the struggle to overcome misinformation is arduous and painful, but it’s worth it. Despite the best efforts of contrarians, *we are winning the debate*. A lot of that is due to people talking to other people, over a beer in a bar, around the water cooler, about an article in the paper, etc. This happens to me a lot, and these days, I am so much better informed, and have encountered so many contrarian arguments before, that without anger, shouting, or personal attacks I generally carry the day. The cool-headed logical approach rarely wins the “shouting match,” but almost always persuaded the undecided.

  30. 30

    Re: Urs “This inevitably points to the fact that there must be other and stronger forcings effective during these times.” What every intervening effects caused the 50s and 60s cooling, only means that the equilibrating to the increased level of forcing was delayed, so that the . Hansen’s 2005 work in Science was based on the GISS-ER model, which had a bias against solar per Roesch 2006., and Hansen, et al, applied that bias twice by using the “effective forcing” for solar he derived from:

    Hansen, J., et al. (2005), Efficacy of climate forcings, J. Geophys. Res., 110, D18104, doi:10.1029/2005JD005776.

    That value reduced the solar forcing applied by another factor of 0.92. The abuility to match 20th century heat flux into the ocean with only GHGs, with a model twice biased against solar, and at a resolution that did not reproduce ENSO behavior is not impressive. If modelers really want to test the solar hypothesis, they should at least acknowledge the consensus factor of two uncertainty in solar forcing increase, and use that. In the meantime both Hansen papers should be retracted. The credibility of climate models will be increased when they stop being unchallengable paper mills, and when corrective action is occasionally taken.

    Roesch A. (2006), Evaluation of surface albedo and snow cover in AR4 coupled climate models, J. Geophys. Res., 111,D15111, doi:10.1029/2005JD006473.

    The the URL I supplied for futher discussion, of the implications of the Roesch result.

    [Response: No, no. and wrong. Your supposed bias against solar forcing due to the minor surface albedo offsets is trivial as has been demonstrated to you myself, and even from Isaac Held. There is no ‘double’ application of solar efficiacy in the Hansen et al results – think about it! ‘Efficacy’ is a model result, not an input. Finally your idea that models get improved by retracting papers is, shall we say, a little bizarre. Model improvements are always ongoing – both as data improves and better physics is incorporated. Those improvements will show up in the next set of papers. If we haven’t done exactly the sensitivity experiment you want, then download the model and do it yourself – it’s complicated, but it’s not that hard. – gavin]

  31. 31
    Eli Rabett says:

    Let me reply <>tongue in cheek<> to John McCormick and Grant. Rapid climate change will take at least 30 years. Geologists who think like rocks don’t pay much attention to such short periods. Within 2 sigma I will be dead in 30 years. Why should I care? YMMV. <>/tongue<>

  32. 32

    Gavin, The GISS-ER globally-annually averaged surface albedo is approximately 0.131 compared to satellite observation values of 0.121 and 0.124. To gain perspective apply the globally-annually averaged solar surface flux of 198 W/m^2 (Kiel and Trenberth, 1997) to get an error of 1.4 to 2W/m^2. How can you and Isaac argue that this is small when it is larger than the heat flux of 0.8W/m^2 into the ocean that was the result of the Hansen, et al 2005 work.

    Yes, the efficacy is a GISS-ER model result (and thus biased against solar), but it was reapplied as an input in Hansen’s 2005 Science publication (bias doubly applied).

    All the AR4 models have a bias against solar, attribute the recent warming to GHGs and manage to fit the 20th century data, despite having climate sensitivities that vary by over a factor of two. The models are still too facile and poorly validated and constrained.

    The Hansen papers were particularly egregious in applying the anti-solar bias twice, using efficacy forcings based on the atmosphere that ignore how much more strongly solar is coupled to the ocean, and for getting conclusions about the climate past the peer reviewers that went beyond the model results.

    [Response:Martin. This is getting tired. We explained the difference that an offset in the mean could have on the sensitivity to solar (small). For the last time, I assure you that efficacy is not applied as an input. The only egregious thing here is your continued inability to listen when people try and explain things. Conversation over. -gavin]

  33. 33
    buck smith says:

    I recently came across this article which advocates something I have long thought about – geo-engineering solutions to global warming:

    I think Edward Teller and / or some Russian scientists have also advocated this before. Besides the idea of putting something in orbit to block some of the sun’s incoming radiation, there may be other geo-engineering solutions. For example if rising sea levels is the big problem that comes form global warming, maybe we can use nuclear explosions to open up some caverns to maintain the sea level constant.

    Part of being a scientist is to look at all solutions to a problem. It is important to remember that CO2 is not in and of itself a toxic compound. It is a vital nutrient for plant life…

    [Response: Look at: – gavin]

  34. 34
    Bryan Sralla says:

    Re: #31 Both of Eli’s comments. 1)The AAPG is not under control of big oil. In fact, I would say that most of the membership does not work for major oil companies. Much of the AAPG current policy position has come from some papers published by Lee Gerhard of the Kansas Geological Survey, and an AAPG past president, neither of whom are associated with big oil. You are just wrong about this.

    On your second statement, geologists, and specifically petroleum geologists, have looked at more of earth’s history than any other group of scientists. Who else gets the opportunity to study marine fossils coming from a well drilling at 8 km deep? A job like this gives you a little different perspective. Many of us believe that the public should be educated on this perspective in order to place recent change in context. Such a perspective however, does not mean that we do not move out of the way of a hurricane or tsunami when it approaches. It does not mean that we deny the workings of physics. We understand that if you do not adapt, you become part of the geological record.

  35. 35
    muller.charles says:

    #24 Eric Response
    “I would like to emphasize that everyone in the scientific community understands and accepts that even some of the 20th century warming is due to natural changes”

    That’s a point I don’t clearly understand. When I look at IPCC 2007 draft (Table 10.2.1) about model intercomparison for simulation of 20th century and projection in 21st century, it appears that a large majority of models do not include any solar forcing. How is it possible if 1910-40 warming was at part solar-induced ? I suppose the signal of temperature trend on this period is very weak (equivalent to chaotic variability). But if all 1900-2000 warming is attributed to GHG’s in these models, how do they avoid an overestimation of GHG’s climate sensitivity for 2000-2100?

  36. 36
    chris says:

    Re #33

    “It is important to remember that CO2 is not in and of itself a toxic compound. It is a vital nutrient for plant life…”

    Isn’t that a ludicrously pointless statment? Of course CO2 is a “vital nutrient” for plant life! CO2 plus water = plants (add a few minerals or N2-fixators, as sources of nitrogen, phosphorus, sulphur and metal ions etc.). Without plants no animals could exist. Only bacteria and other microorganisms could exist without plants.

    But so what?! We’re not talking about the role of CO2 as a constituent of plant and animal matter. We’re talking about CO2 as a greenhouse gas that is the dominant variable in the composition of the atmosphere. CO2 functions as a “vital nutrient” at atmospheric levels of 180 ppm (glacial levels), or 280 ppm (interglacial levels), or 385 ppm (atmospheric CO2 levels now), and it will function as a “vital nutrient” at levels of 480 ppm or 580 ppm or 780 pp or 1080 ppm or 1580 ppm or 5080 ppm or whatever.

    However, CO2 levels also “set” the Earths temperature in its role as a greenhouse gas. Plants will do fine when CO2 levels reach 1080 ppm (say). It will act wonderfully as a “vital nutrient”. Some plants will, thrive! Unfortunately, animals by and large won’t. Including us…

  37. 37

    Gavin, I quote from the Hansen, et al, 2005 paper “Figure 1A summarizes the forcings that drive the simulated 1880 to 2003 climate change. Among alternative definitions of climate forcing (9), we use the effective forcing, Fe. Fe differs from conventional climate forcing definitions (11) by accounting for the fact that some forcing mechanisms have a lesser or greater ‘efficacy’ in altering global temperature than an equal forcing by CO”

    And this quote: “Solar irradiance is taken as increasing by 0.22 W/m2 between 1880 and 2003, with an estimated uncertainty of a factor of 2 (9).”

    So, looking at the efficacy paper, as near as I can tell, this 0.22 W/m^2 is leans 0.247 from table 3, multiplied by the efficacy of 0.92 giving 0.227, which for some reason is rounded down to 0.22, perhaps because the uncertainties are viewed as “subjective”.

    [Response: The model uses the actual irradiance from Lean as input. The ‘forcing’ that is associated with that, is a diagnostic which is plotted and included in the tables. Nothing in how the forcing is defined, nor how it is compared to other forcings has any input into the model at all. The 0.22 is the effective forcing from 1880-2003, based on the adjusted forcing of 0.24, based on the total irradiance change given in Lean (2000). -gavin]

  38. 38
    chris says:

    Re #34

    Great! Geologists (and “specifically petroleum geologists”) have great insight into the distant past. They can “educate the public” on this perspective! No doubt they (geologists) can point out that not only have CO2 levels been higher (much higher!) in the past. They can also point out that it’s been hotter too.

    So nothing to worry about then!

    I have no problem with geologists “educating the public” about the geological history of the Earth. It’s a fascinating subject. However it would be extremely unfortunate if this “education” was used as a means of suggesting that we have nothing to worry about since, hey, it’s been hotter in the past and CO2 levels were higher! I would hope that the geologists “educating the public” were honest enough to tell the whole story and tell us (for example) that although it was a bit warmer during the last interglacial 130,000 years or so ago, sea levels were 10-12 feet higher. We might want to incorporate the latter point into our consideration of how much or little we care about whether it gets a bit warmer.

    One could question the value of the geologists input even if it were to be fully honest. Because, after all, mankind has only been on the Earth for 200,000 years or so. Hominid evolution encompasess a period stretching back 4 million years. Surely these are the relevant timescales for considering the climatic conditions within which we might be comfortable. Our civilisations have “acclimatised” themselves to a rather narrow range of climatic conditions. We need to consider the extent to which we can accomodate ourselves to climatic variations that bracket those within which we have evolved.

    One might question the relevance of the “geologists education of the public” with respect to climatic variations involving vast difference in temperature or atmospheric CO2 levels that might have existed in the distant past that bear little resemblance to those existing either now, or during the entire period of mans recent evolution.

  39. 39

    Whoops, no Lean’s Fi is 0.288, not 0.247, so I don’t know where Hansen’s 0.22 comes from, even though the efficacy paper is given as the citation.

  40. 40
    Steve Sadlov says:

    “Aging shills” etc, etc …. AGW savvy Joan’s of Arc and Men from La Mancha, standing up to “the Man” (man!) who reputedly funds the skeptics … etc, etc. If only. In truth, the current money is on AGW, not on skeptical thought. The skeptics are the new radicals, the AGW true believers are the current orthodoxy / establishment. Witness recent bets on growth in the Carbon Credit trading futures.

  41. 41
    John L. McCormick says:

    RE # 40,

    Steve, you said [In truth, the current money is on AGW, not on skeptical thought.]

    The skeptical thought machine seems to be well oiled if the Exxon contributions to CEI are any indication. Maybe Myron is a petroleum geologist in his free time?

    Competitive Enterprise Institute has received $2,005,000 from ExxonMobil since 1998.

    $85,000 ExxonMobil Corporate Giving
    Source: ExxonMobil 1998 grants list

    $230,000 ExxonMobil Foundation
    general support
    Source: ExxonMobil Foundation 2000 IRS 990

    $280,000 ExxonMobil Foundation
    Source: ExxonMobil 2001 Annual Report

    $205,000 ExxonMobil Foundation
    50K congressional briefing program, 140K general operating support, 60K legal activities
    Source: ExxonMobil 2002 Annual Report

    $200,000 ExxonMobil Corporate Giving
    140K general operating support, 60K for legal activities.
    Source: ExxonMobil 2002 Annual Report

    $25,000 ExxonMobil Corporate Giving
    Annual Dinner
    Source: ExxonMobil 2003 Corporate Giving Report

    $440,000 ExxonMobil Foundation
    General Operating Support
    Source: ExxonMobil 2003 Corporate Giving Report

    $90,000 ExxonMobil Foundation
    General Operating Support
    Source: Exxon Giving Report 2004

    $90,000 ExxonMobil Foundation
    Global Climate Change
    Source: Exxon Giving Report 2004

    $90000 ExxonMobil Foundation
    Global Climate Change Outreach
    Source: Exxon Giving Report 2004

    $90,000 ExxonMobil Foundation
    General Operating Support
    Source: ExxonMobil 2005 DIMENSIONS Report (Corporate Giving)

    $180,000 ExxonMobil Corporate Giving
    General Operating Support
    Source: ExxonMobil 2005 DIMENSIONS Report (Corporate Giving)

  42. 42
    Joel Shore says:

    Re #33 “Part of being a scientist is to look at all solutions to a problem. It is important to remember that CO2 is not in and of itself a toxic compound. It is a vital nutrient for plant life…”:

    However, another part of being a scientist is to realize that one sometimes does not have an infinite amount of time to look at all solutions and one might have to prioritize what one investigates, at least in detail. Another part is to recognize that there are always surprises and unknowns so that there should be preference given to simpler solutions (such as don’t do what is screwing everything up) rather than complex “swallow the spider to catch the fly” solutions.

    This is not to say that some geo-engineering solutions are not worthy of some consideration (although your idea of creating caverns for sea water by nuclear explosions is probably one we could put into that not worthy category pretty damn quickly!)…But, it seems to me that some people are using the idea of looking into these just as a way to avoid making any changes that Exxon and Western Fuels Association may be uncomfortable with!

    And, along the lines of unexpected things…It is starting to become better understood that, in addition to climatic effects, the increasing levels of CO2 are changing ocean chemistry in detrimental ways. Surprises like this point out exactly why a focus on screwing the ecosystem and climate system up less are often wiser than trying to tinker with the system by doing things that we hope can offset some of the negative impacts of our original effects.

  43. 43
    Paul Biggs says:

    #15 – Not the first time passive smoking has surfaced in a climate science weblog – as a life long non-smoker I would point out that large diesel engines emit the two most carcinogenic chemicals known to science, particularly when the engine is under load. These are 3-nitrobenzanthrone (3-NBA) and 1,8-dinitropyrene (DNP) and could be at least partly responsible for an increase in lung cancer in urban areas. Another reason for reducing fossil fuel use/burning fuel more cleanly and another reason to be cautious about the evidence for passive smoking, which isn’t as good as the evidence linking smoking and cancer.

  44. 44
    Bryan Sralla says:

    Re #39: Thank yor for your perspective. I do not agree with it however.

    The geological perspective tells us that a certain amount of earth system change (not just surface temperature) is beyond human control. For that portion of change, mitigation is the only rational remedy. How do we deal with things like volcanic eruptions or possible weakening or flip of the earth’s magnetic field? How might future man deal with a Milankovich cycle or a large collisional impact from space?

    Geology also serves as a kind of baseline to try and asertain how much of the earth system change is due to us. Without this perspective, it is really hard to view these changes in a meaningful scale.

    Most geologists see that man is altering the earth system in a variety of complex ways from damming and diverting rivers, to agriculture, to GHG and aerosol emmisions. Though helping to better understand these, geologists might also suggest different behaviors which might be beneficial, and others that would have a counterproductive or no impact.

    I believe that RC favorite scientists like Micheal Mann would agree, that all disciplines of the earth sciences (including geology) have an important role to play.

    [Response: Many of the greatest scientists of today, including many who study climate, were trained as geologists, originally.
    But, this is getting way way off topic. I plan to shut down comments on this post, unless they start being more relevant. No offense intended to this particular comment. –eric ]

  45. 45

    Re: #37, Gavin, the plot in figure 1A for solar irradiance appears wrong. It only show one-sixth of watt, peak to trough for the last cycle. The center of that cycle is only 0.2+/-0.02W above zero. Peak to trough should be about 1.3W. Is that a plot of the actual forcing data?

    [Response: It’s a plot of the forcings (Fe). So 1.3*0.7/4*0.92 ~ 0.22 after taking everything into account. – gavin]

  46. 46
    Bryan Sralla says:

    Re: #42 Joe, the reason Exxon is investing money in CO2 sequestering technology is that it may help their bottomlime. Pumping CO2 into some oilfields (miscible flooding) can dramatically increase the recovery factor, leading to more oil reserves. Pumping CO2 into a coal or organic shale causes it to produce more methane gas. If domestic American oil producers had a ready source of CO2 (strip CO2 from the atmosphere?), some recent studies have shown it might increase recoverable oil reserves in the US alone by up to 20 Billion Barrels (equivalent to a mega-giant middle east oilfield). I know, many will ascribe all sorts of evil intentions to this, but who would you rather buy your oil (gasoline, aviation fuel) from: Hugo Chavez, Mahmoud Ahmadinejad, or Exxon? They all sell it.

  47. 47
    Eli Rabett says:

    Well Bryan, it seems to me that the timescale that geologist professionally think about is a mite longer than the situation we are currently confronted with, and therein lies a problem. As to control of professional organizations, well, there is a huge petroleum industry (and a pretty huge chemistry one also) and I rather suspect that the industry has a very large influence on the organizations.

  48. 48

    So the 0.92 factor for the efficacy of solar was applied to the forcings used in the Hansen 2005 Science paper and run through the GISS-ER model again.

    [Response: Sigh….. Try to think about it. The graph is there to compare the different forcings acting on this model. Since we are comparing forcings, the effective forcing is an appropriate metric. This is a diagnostic of the model, not an input field. The inputs remain the same and are available directly from the GISS website. – gavin]

  49. 49

    Gavin, Peak to trough 1.3 mapped to the surface of the earth (divide by 4) and applying the 0.92 factor from the GISS-ER based efficacy paper gives a peak to trough of 0.299. The peak to trough in the plot is about 0.16. The 0.7 is fine for integrating the sinusoidal, but should not impact the peak to trough. I assume that the solar irradiance increase from lean is larger than the 1.3 in order to get to the 0.22 figure.

    [Response: 0.7 is for the albedo… – gavin]

  50. 50
    chris says:

    Re #44

    I have no problem with “the geological perspective” in general terms! But you need to be clear about what this “perspective” is and how it relates to present day issues. Of course a “certain amount of the Earth system change” is beyond human control. But all of these things (you cite “volcanic eruptions” and “weakening or flip of the Earth’s magnetic field” or “Milankovic cycles” or “large collisional impacts from space”) are very low probability events in the foreseeable future (apart from volcanic events, and the common-or-garden variety of the latter are of no particular concern).

    One needs to be more precise about the “geological perspective” in relation to climate change. The geological perspective gives a fascinating insight into the evolution of Earth processes of the timescale of many 100’s of thousands years and longer. But global warming is an issue that impacts right now and will do so during the coming decades. The geological perspective, however fascinating, doesn’t offer great insights into our immediate problems which are rather clearly defined (too much CO2 and other greenhouse gases being pumped into the atmosphere in too short a space of time!). That’s not to say that a study of geological processes, current and historical, won’t continue to provide insight into to the workings of the Earth. But that’s not really the key issue at present!