A Few Things Ill Considered

Hansen Has Been Wrong Before

Posted by coby on April 27, 2006
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This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

Objection:

In 1988 Hansen predicted dire warming over the next decade and he was off by 300%. Why in the world should we listen to the same doom and gloom from him today?

Answer:

While it may well be simply ignorant repetition of misinformation in some instances, at its source, this story is a plain and simple lie.

In 1988, James Hansen testified before the US Senate on the danger of Anthropogenic Global Warming. As part of that testimony he presented a graph that was a part of a paper published soon after. This graph had three lines on it, representing three scenarios based on three projections of future emissions and volcanism. Line A was a temperature trend prediction based on rapid emissions growth and no large volcanic event and was a steep climb through year 2000 and beyond. Line B was based on modest emissions growth and one large volcanic eruption in the mid 1990′s. Line C began the same as in B but with reductions in the growth of CO2 emission by the turn of the century, the result of hypothetical government controls, and also had the same volcanic eruption as scenario B.

As it happens, Mt Pinatubo did erupt in the 1990′s, though early in the decade, not in the middle, and emissions have grown at a modest rate in the years since Hansen made this testimony. In other words, the forcings scenario of Line B in this graph was remarkably similar to what actually came to pass. It also just so happens that the observed temperature trend has matched very closely with the prediction represented by Line B. James Hansen was right on the money and the models he used proved successful.


(Image borrowed from Rabbet Run with much gratitude! Click here for a larger version)

Unfortunately, when Patrick Michaels made his testimony before the congress in 1998, ten years later, he saw fit to erase the two lower lines, B and C, and show the Senators only Line A. He did so so that his testimony that Hansen’s predictions had been off by 300% would be believable. He lied by omission. This lie was picked up by Michael Crichton in his novel "State of Fear" (as one of many omissions, confusions and falsehood presented in that book, see this Real Climate article).

To my knowledge Patrick Michaels has never owned up to this, either with an apology and retraction or with an explanation, and consequently this urban myth continues to this day.

RabettRun has some more detail and illustrations here.

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

“Hansen Has Been Wrong Before” was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.

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Comments

  1. #1 Tim Wells
    August 21, 2008

    This data is from Hansen at GISS[and is therefore suspect],and it does not show the dive in temperatures for 2007 and 2008.In any case temperatures are not even adherring to scenario C,let alone A and B.Just remember, Scenario C was if there was sustantial action taken worldwide to limit emissions.No such action has been taken,and the temperatures observed are still well below the line.So much for Hansen’s predictions.

  2. #2 coby
    August 21, 2008

    Tim, Please open your eyes. 2007 is there, 2008 is not over so it would be a bit premature to have it! There has been no “dive” in globally and seasonally averaged temperatures, not in GISS or in CRU. The observational line is not below scenario C.

  3. #3 Tim Wells
    August 25, 2008

    Coby,please open YOUR eyes and see that the black line[Hansen's suspect GISS data]is BELOW the purple line of scenario C.If you take the more reliable Hadley centre data,the gap is even greater.And I repeat,Scenario C was the concerted,worldwide emissions abatement scenario,which has not happened.What has happened,in terms of emissions is between scenarios A and B.So why hasn’t the temperature even kept track with scenario C?? When is Hansen going to admit that got it terribly wrong in 1988?

  4. #4 coby
    August 25, 2008

    Hi Tim,

    I was referring to the red line, labelled “Station Data” which I believe is the GISS analysis. The black CRU, which you think is more accurate (because it is lower?), does not include the arctic where warming is predicted and observed to be much greater. Regardless, all the lines B, C, red obs and black obs are well within the range of natural variability from each other, so I don’t see the utility in analysing the differences this much.

    Scenario C did have hypothetical gov’t controls, but not until the year 2000, so no difference is to be expected between that and B until ofter such time.

    Glad we have abandoned the alleged “dive” in 2007-08.

    Hansen said temperatures would rise, they have risen well within the ball park of his predictions, let’s get past this erroneous talking point.

    BTW, while you are taking people to task, what is your opinion on Patrick Michaels’ misrepresentation to congress? Does this not warrant some outrage?

  5. #5 Tim Wells
    August 27, 2008

    Well for a start this entire graph is from Hansen and it dates from May 2007.The rest of the data for 2008 are not there.For an update to 2008 go to Climate Audit and search for Hansen,and get a complete update on recent data and Hansen’s projections.One reason why Hansen’s data is not reliable is because he refuses to publish his methodologies,and that is why people like Steve McIntyre are always correcting him.[Eg Hottest year 1934].The other reason is that GISS uses only Land only[red line]data and land-ocean[black line]data.GISS does not use satellite data.

    “The black CRU…..does not include the arctic…”
    Where did you get this from?In have never heard any such thing.
    “Scenario C…..not until the year 2000.”
    Once again where did you get this from??I have never heard of this.But in any case,the fact is that temperatures have NOT followed Hansen’s forecasts,not even for the abatement scenario.
    The “dive” in 2007 and 2008 is alive and well;it is only that Hansen’s graph that does not show it.Once again go to Climate audit to look at the latest satellite graph.
    Re:Michaels.
    Yes,Michaels should have used the full 3 scenarios and not just scenario A.That was misleading.

  6. #6 pough
    September 2, 2008

    …people like Steve McIntyre are always correcting him.[Eg Hottest year 1934]

    This, to me, is one of the most fascinating parts of paying attention to climate issues. The 1934 issue is a fantastic example of McIntyre’s modus operandi, as well as a great look at the way compelling misinformation picks up additional meaning, Katamari-like. Climate is an interesting field on its own, but you get the added bonus of communication, maniupulation, politics and PR thrown in for good measure!

    1934 has always been a high-temp year in the data record, but only for the contiguous states, not globally. In fact, Hansen himself pointed out in 2001 that since 1998′s slight nudge past 1934 was within the error bars, 1934 still had the record for US temps. (The notorious alarmist Hansen!) When McIntyre pointed out an odd blip in the data, corrections were made (not by mcIntyre) that put 1934 a touch ahead of 1998, but still within enough error range for them to remain tied. They went from tied for first place with 1998 a nose ahead to tied for first place with 1934 a nose ahead.

    And keep in mind that when it came to global temperatures, 1934 is still way back there – nowhere near 1998.

    But somehow this came out as McIntyre correcting Hansen. Not only that, but he did a masterful misdirection in his communication. Here’s how he did it. Pay close attention.

    Hansen used to go on about 1998 being the hottest year, but McIntyre pointed out an error and now 1934 is the hottest year! You don’t hear Hansen talking about 1998 any more.

    See the switch? It’s true that Hansen talked about 1998 being the hottest year globally, but never the US temps. He specifically noted that 1934 had the record, even before McIntyre’s “correction”! And so 1998 (global) gets beat out by 1934 (US), somehow. Not only that, but in the meantime, 2005 edged past 1998 in the GISS record. (And the GISS site is careful to mention that 2005 and 1998 are within the error bars of each other.) Why would anyone go on about 1998 being the hottest year if 2005 has superseded it?

    McIntyre dropped the global temps down his left sleeve and pulled the US temps out of his right and all over the blogosphere you get comments like the one above. Presto!

  7. #7 coby
    September 5, 2008

    The other intersting “viral myth” is this line about “refuses to publish his methodologies”. I would bet that this is just a morphing of the “Mann et al won’t publish their data” wyth.

    Tim, care to elaborate?

    I did not answer your other points (eg “dive in 2007-08″) because you simply ignored my previous response to exactly that fallacious claim. It is impossible to have a useful dialogue if you do things like that.

  8. #8 tim wells
    September 7, 2008

    Hey Pough,I really dont get what you are going on about.GISS admitted the error by revising their data within a couple of days of McIntrye’s correction.McIntyre has never said it was global temps and niether did I.

  9. #9 timwells
    September 19, 2008

    In any case we are getting off thread.The case in point is that Hanson’s predictions are not worth the paper that they are written on.What I can not understand Coby is why you are unable to admit what is obvious.That is,all of Hanson’s predictions have failed!!You can make as many excuses as you like for them,but the fact remains that temperatures have gone DOWN while CO2 levels have gone UP.The exact opposite of what Hanson predicted.

  10. #10 coby
    September 19, 2008

    Okay, tim, this is no longer worth pursuing. In 1988 Hansen predicted .4oC rise by today via the blue line, we have observed the red and the black lines (different data sets), they are within uncertainty boundaries of each other. Yet you see the temperature going down. Who’s wasting (virtual at least) paper?

  11. #11 timwells
    September 21, 2008

    Coby,the graph you are referencing from is from 2007!It is out of date!No up to date data agrees with Hansen.

  12. #12 dp
    September 25, 2008

    Why does the middle line have temperatures levelling off after 2010? also that bit about the bottom line assuming worldwide action to cut emissions. Hanson should know that even if all emissions ceased tomorrow warming would continue for decades.

  13. #13 coby
    September 25, 2008

    dp,

    You’d have to check the detailed emissions scenarios Hansen et al used in that paper to know what the trajectories were.

    As for continued warming after cessation of emissions, maybe that was not know at the time, or at least it was not buitl into the models. But you are correct that a complete stop to all emissions would still see the temperature rise for several decades, though leveling off, not increasingly.

  14. #14 timwells
    September 29, 2008

    So coby what has caused the fall in temperatures since 2001?Hanson did not predict it,so what has been the specific cause?The sun? Aerosols?

  15. #15 Robert Grumbine
    September 29, 2008

    dp, coby:
    Warming continuing for decades after cessation of emissions was known (at least I knew about it, though I don’t remember which papers it was from) by the time of Hansen’s 1988 paper. Actually, if you’d asked scientists in the area even by the later 70s, I expect they’d have said that they expected temperatures to rise for some time after emissions stopped.

    The thing more involved is that ‘emissions stop’ scenarios were not interesting. There has been no reason to believe that emissions would ever stop, so why bother wasting an expensive GCM run on such an implausible scenario? The answer is public, not scientific. The science already realized it’d be some time to come to equilibrium. The public has thought that as soon as we stopped making new emissions, everything would immediately return to normal (whatever that is).

  16. #16 paul
    September 29, 2008

    No Tim, you’ve got it all wrong. There hasn’t been a drop since 2001. Check out the “Warming stopped in 1998″ page for details. Well, I ok, there has, but only if you look at the actual data – if you smooth it by averaging over a (convenient) number of years, it levels off.

    Anyone using a 7-8 year trend to suggest changes in the climate is clearly a moron. Anyone using the 20 years (at most) though from late 70s to 1998 as proof of global warming is clearly a far-sighted, hero of our times.

    So they didn’t predict it no, but this isn’t important, as it is just a small blip in a general trend upwards. Now I know we should be proving that this general trend upwards (if it indeed exists) is due to humans, but basically we can’t. We just going to assert that when the temperature goes up, it is due to human generated CO2, but when it doesn’t, it’s because of something else overriding the, erm, primary driver.

  17. #17 timwells
    October 3, 2008

    Thanks for your comments Paul.Another question for Coby.
    Coby,how would you falsify the theory of AGW?

  18. #18 Harald Korneliussen
    November 26, 2008

    The “Hansen has been wrong before” line was recently repeated in the Sunday Telegraph, which you commented in your “warmest October on record” article. However, there the argumentation that Hansen had been wrong before was different.

    Since Hansen appears to be a frequent target for personal attacks, I hope you keep up the good work.

  19. #19 Ivan
    December 10, 2008

    I think that you are all mixing several things together in your argument. We have several questions:

    1. Is there a warming trend?

    Observing just a few years is not enough to make generalizations about trends. If that could be done, you could have claimed a global cold period was beginning in the first half of the 1960′s, the mid 1970′s, twice in the 1980′s and twice in the 1990′s. You could also claim that global warming was beginning in the same periods, just after the cooling down finishes.

    But that is not proper use of data. I am not a climatologist, but I know that there are many factors influencing temperatures during the year, especially since I presume that the given empirical observations are an average (or something similar) of regional data. So, you have to take averages of several years to smooth out the annual fluctuations. That would show a clear trend of warming through several decades, although the trend is clearly visible even with annual data.

    2. Will this trend continue?

    Again, from this data, we can, without doubt, conclude that it will. Throughout the 50 year period presented, there is no sign of the trend changing. If indeed there is a cooling period from 1998 or 2001 (and as hard as I try, I can’t see the cooling on the chart), then, judging from previous data, this will just be another cooling-warming cycle, at the end of which, a new temperature peak will be reached.

    Oh, and someone mentioned that the B line levels off after 2010. It does not. The trend is still rising. It also “levels off” in the 1990′s, even falls a bit, but again, you cannot use annual data.

    3. Everything else

    That is about all that can be concluded from this data chart alone. The data chart can be used as evidence in other debates, juxtaposed with CO2 concentrations, economic growth charts, put into proper context of a myriad of other factors affecting the climate etc, but on it’s own, it is not evidence of anything, expect that there indeed has been a warming trend in the past 50 years.

  20. #20 Ivan
    December 10, 2008

    4. Hansen’s prediction

    Sorry, I forgot the most important thing. It seems that both lines for the empirical data broadly fit to Hansen’s predictions (and hindcasting) for the entire period, with the red line being a better fit for the past few years. I am no expert, so I will not go into which line has more scientific weight, but even if we use the black line, it’s only a question of whether we will reach the estimated temperatures a few years later.

    Also, the fact that for the past few years, the black line was below even scenario C doesn’t mean anything, since you also had forecasting periods for which it was above both scenario C and B. Again, just using these charts does not allow us to make generalizations, without knowing what is causing this warming, which is a different topic.

  21. #21 Ivan
    December 10, 2008

    5. Question?

    What I am interested in is why are the two lines for empirical data getting further apart? Where could I find the original research, which presumably has more explanations and metadata?

  22. #22 paul
    December 11, 2008

    Well Ivan, I also think this particular issue is being obfuscated a little. If we can return to the title of this post, the question is about Hansen’s predictions. I am interested in whether Hansen actually predicted anything which was falsifiable. You and Coby have said between you:

    “Regardless, all the lines B, C, red obs and black obs are well within the range of natural variability from each other, so I don’t see the utility in analysing the differences this much.”

    “It seems that both lines for the empirical data broadly fit to Hansen’s predictions (and hindcasting) for the entire period,”

    “In 1988 Hansen predicted .4oC rise by today via the blue line, we have observed the red and the black lines (different data sets), they are within uncertainty boundaries of each other.”

    If you want to say that the red and black lines are within the error bounds for scenarios B and C, then I will take your word for this – so we have an idea of what you accept the error bar sizes are here. But this of course suggests that his scenarios B and C are within the error bounds for each other up to now. And, given that blue and green are a similar distance apart from 2008-ish onwards and the incredibly innaccurate predictions made by scenario A, we can say that they are not in fact clearly separable into two separate scenarios either. This makes the whole business of differentiating between these scenarios somewhat suspect from the start.

    Further, with error bars this size, there has barely been a rise from 1990 to 2008 in the black and red lines. So, what gives? Can the error bars on the one hand be large enough to say that these predictions are all valid as they are all basically the same, yet on the other hand be so small as to guarantee that there has been a rise in the last 10 years or 20 years. Maybe they are? As you must have already done the calculations to be so certain (I’ve not done the calculations, but I’m not certain about anything, I’m just saying we should continue the debate as the AGW case remains unproven), can you tell me some of your numbers?

    Then, based on this, can you give me a scenario (ie. temperature now) after which you would have said Hansens’s predictions are wrong? I say this because I think they predictions as they are being interpreted now are so vague as to be worthless and so maybe you could prove me wrong by outlining how they could have been falsified.

  23. #23 Ivan
    December 13, 2008

    Paul,

    I hope I didn’t give the impression of being so certain about anything concerning climate, since I am no expert in that field. I was merely trying to point out a few thing about this debate. You are right about going back to the original question about Hansen’s prediction.

    You are asking for a concrete temperature which would falsify Hansen’s predictions. I cannot give you that. Again, giving an average temperature for this year or that, or even an average for a few years, could not falsify a hypothesis about the prospect of a global warming trend. (I emphasize trend.) What could falsify it would be an observation that the trend is reversing or stopping.

    I don’t have the concrete numbers, but roughly from the graph, and taking averages for decades, I guess that the annual temperature change in the 1960′s was perhaps even a bit below 0oC, for the 1970′s a bit above 0oC, for the 1980′s around 0.25oC, for the 1990′s around 0.5oC, and for the 2000′s up until 2007 around 0.7oC, but we have to wait until the end of the decade to be sure.

    You have to give a reason why you think this trend will not continue, or that it will perhaps reverse.

    But to make it clearer why I think that the burden of proof falls on you, let’s look at the graph. The large drop in 1992 (after a volcano in 1991), is as warm as 1973. The average for the 1990′s is higher than peak years in the previous decades. The average in the 2000′s (up until now at least) is topped only by the peak in 1998, which is the highest peak before 2000′s. 2005 and 2007 top 1998.

    Even if 2008 turns out to be relatively cold, again, judging from this data, that is not going to change the trend. The average for 2000’s would still be higher than the average for the 1990’s. There were cold years before (meaning a relatively high temperature drop from the previous year) – say 1969, 1976, 1992, 1999 – and perhaps 2008 is going to be such a year again. But if 2008 turns out to be a very large drop, as large as the largest in the past (say 1991-1992, or 1973-1976), it’s still going to be warm approximately as the average for the 1990’s.

    I believe that the most important thing about predictions such as Hansen’s is not the scenarios, but the general idea – in this case, the idea is that global warming will continue. It is not that important whether the average temperature change is going to be 0.7oC or 0.6oC or 0.8oC. Or if you are going to have a peak or a drop because of a volcano or El Nino, or whatever. Or even if the average temperature change between decades is a bit lower between decade 2 and decade 3, than between decade 1 and decade 2.

  24. #24 paul
    December 15, 2008

    Ivan – I’m sorry, I fundamentally disagree with your line of thinking.

    Firstly, if you can define what a “trend” is then we can begin to decide what criteria we can apply to see if it exists or has stopped. I have asked a number of times on this site for people to define what they mean by a trend – i think I know the reason why I don’t have an answer yet, but anyone feel free to prove me wrong by providing a definition that I can use. My own understanding, until told otherwise, is that it is used to define a “reasonably” constant change in temperature over a period of time long enough to be considered more than weather, and that 30 years or so is the accepted figure for this. Though I am yet to be convinced that this 30 years is anything other than arbitrary, this is at least a reasonable point to start.

    Note though that using this definition, there is no obvious trend. Temperatures were flat or falling from WW2 to 1975, rose from 1975 to around 1998, and have not risen (or maybe fallen) since.

    http://scienceblogs.com/illconsidered/2006/04/warming-stopped-in-1998.php

    If you think this is definitely a “trend”, maybe you could explain what I am missing.

    Secondly, you’re spending your time explaining to me that the temperature is higher now than it was decades ago. This is not the point. I know this already and I can’t think of anyone worth listening to who denies that the temperature now is around 0.6 degrees warmer than the start of the 20th century, and around half that warmer than it was in 1975. And the greenhouse effect is clear and no doubt that human CO2 has had SOME effect on temperature – the question is whether this effect is insignificant or not. I suggest it is.

    You must demonstrate how much of this rise is due to human generated CO2 and what effect, if any, human CO2 will have on future temperature? You have not addressed this, you simply assume that the “trend” to which you refer is due to humans. This is what I and others in fact seek demonstration of, so if you can do this, please do.
    For example, of this “trend”, earlier you said, “Again, from this data, we can, without doubt, conclude that it will. Throughout the 50 year period presented, there is no sign of the trend changing.” This is of no use – you can’t just look at the data and “decide” that it will carry on, regardless of whether there is any “sign” of it changing. The temperature has always gone up and down by tenths of a degree. What proof is there that ties any of this rise to human CO2? I in fact don’t think that the trend will continue – but if it does, then so what? I don’t have to prove it won’t like you ask – temperature has always gone up and down. I am asking whether this “trend”, or another in future, has anything to do with human CO2. Can you give me your take on the evidence for this please.

    Finally, I couldn’t possibly disagree more with the statement “I believe that the most important thing about predictions such as Hansen’s is not the scenarios, but the general idea”. This is a dangerous road to go down. Anyone who has worked on complex systems knows that the “general idea” can sometimes be very useful, and sometimes be flat-out wrong. What you have to do is put your general idea to test before assuming it is correct. If you tell me that there is no record of temperature since hansen made his predictions that could have falsified them, then charitably I would say that what we should be doing is awaiting to day when they can be verified, not just assuming he is correct. Uncharitably, I would say that this is an absolutely ridiculous statement/scenario – what weight could we attach to a theory that CANNOT be falsified by real world observations?

  25. #25 Ivan
    December 18, 2008

    Paul,

    We are mixing several debates here again.

    1. You said, referring to the trend: “you can’t just look at the data and “decide” that it will carry on, regardless of whether there is any “sign” of it changing.”

    As I said in my first post, I was trying to point out a few things about this debate. Namely, that this evidence – I mean the temperature chart – cannot be used to determine that the warming is tied to CO2 emissions, or anything else for that matter. The chart is just evidence that there is a warming trend. I was merely saying what can be concluded by just observing this 50 years chart. I think I stressed somewhere, and if I didn’t, I’ll do it now, that I do firmly believe that simple extrapolations are not enough to make predictions. We have to know what mechanisms are behind the changes.

    2. Now, the evidence that this is due to human activity, although this was not the topic of this post.

    I do believe the evidence presented to me to support the hypothesis that this warming trend is primarily due to human activity, and that it is not only C02 that is contributing to it. The article that you posted a link to is, I think, good evidence of this, and I do think that you have missed the most important detail on the temperature chart for the last 12.000 years.

    Namely, at the end of the chart, the mark for 2004 is way beyond what we have had in the last 12.000 years. Now, this in itself would not be a problem, since the temperature for around 11.000 years ago is also way colder than later in the period. I do not know – perhaps there were even warmer or colder periods in the vast amount of time that the chart does not cover. However, the problem is the fact that we have had our dramatic temperature rise in just a few decades, which should be (and I believe experts on this) an insignificant period for climate change.

    These decades also coincide with economic growth rates by far higher than anything we have ever had before, especially during the first three decades after World War 2. The temperature growth starts approximately after these three decades. As I said, I am not an expert (I’m an economist), but I haven’t heard about much evidence that some other factor underwent a significant change in this period, except all indicators of our economic output.

    3. Hansen’s predictions, which was the original topic of this post

    I agree with your criticism of my statement about the general idea. Reading it again, the way I put it, there is no way to falsify Hansen’s predictions. I agree that it is extremely dangerous to use general ideas without providing a way to test them. As an economist, I am painfully aware where than can lead a science to. So, I thank you for pointing it out to me that I have, indeed, went down that road. At least I can say in my defense that it wasn’t intentional.

    But, I will try now to more clearly explain in this post why I still think that Hansen’s scenarios are not the most important thing. I haven’t read any of Hansen’s original research on which he built his testimony to the Senate. I do not know what other data he used to come to his conclusions and predictions. If he used only temperature data for the past 40 years (from his standpoint of 1988), then his prediction about global warming was very daring, if not outright unscientific. If he, on the other hand, used a wider array of data (temperature for past centuries, C02 concentrations, etc), which I would guess that he did, then it was a scientific prediction.

    If it is the case that he used a wider array of data, then the concrete scenarios are not the most important aspect of his conclusions. If in 100 years, you’ve had a temperature change which would have normally taken anywhere between 3-4 to 15 times as much time (approximate estimate from the temperature chart for the past 12.000 years), with a significant portion of this growth concentrated in the last part of the period, then it is a schoolbook example of exponential growth, and then it is really not important whether the temperature changes for the next two decades are +0.5oC, +0.6oC or +0.4oC.

    To use a metaphor, that would be like discussing the impact of a hand-grenade explosion by talking about whether you had 1000, 800 or 1200 pieces of shrapnel.

    Back to the temperature change, I believe that if you had a downwards trend for 10.000 years, and then, in just 30 years, gained back all the temperature that you lost, then there clearly is an external factor causing this trend, and the only significant external factor that has changed is the human economy.

    * Looking at the temperature chart for the past 12.000 years, I do have to say that I did my above analysis mixing the black (trend?) line, and the data for 2004, which is, I presume, not trend data. I do not know what the other lines are, but if they also represent temperature measures, then I can see your point about having as large temperature swings as we have today in the same amount of time that we are dealing with in this post.

    I cannot find where the 12.000 year temperature chart is from. If you, or anybody knows, please post a link or something, so that I may look at what the other lines are.

    Still, just looking at temperature trends is not enough. Again, I stress out that we have to look at the mechanisms of climate change, not just the simple numerical data that we non-experts can understand.

  26. #26 paul
    December 19, 2008

    Ok, the evidence that this is due to human activity was not the topic of this post, but is the fundamental question on any debate about AGW. Valid though they are, I’m not personally interested in debates which assume this is true and then consider the consequences. The question is whether the rise (or “trend”) of which you and others speak is due (or at least primarily due) to humans.

    And Hansen thinks this is true – he has a theory, and based on his understanding of the problem he made some very public predictions. To evaluate whether observations support his theory or not, we can evaluate how his predictions performed. I suggest not well. I further suggest that the range of temperatures over the last 20 years inside which his theory and predictions are still considered valid is so wide as to be make them essentially meaningless and unfalsifiable.

    Fair enough, I accept your first point, that I took your remarks a little out of context. And you appear to be saying that the trend you refer to is the one that started in 1975

    “especially during the first three decades after World War 2. The temperature growth starts approximately after these three decades.”

    So, again I point out that this means that the rise you are basing all this on is nothing more than a 20-odd year rise, admittedly a fairly sharp one, but no sharper than the one at the start of the century which was not accompanied by the same level of econonic activity. So your claim that this is unprecedented is not really valid.

    Also, since then, there has been an equally clear 10-year or so flattening out (or even drop) of the temperature. And I’m told that the rise is just obviously a “trend” that means we’re all going to be barbequeued and the second is obviously just noise or weather or whatever and is irrelevant. I’m sceptical about this to say the least.

    You’re sure that this rise is due to human CO2? And that it will continue? How? I and others have been through this before and won’t rehash it all again. Maybe you want to reply to my unanswered questions?

    http://scienceblogs.com/illconsidered/2008/10/what_is_the_evidence_that_co2.php#comment-1206744

    And finally, just because you can’t think of anything else that has changed, this most absolutely does not mean that the rise must be due to humans.

  27. #27 skip
    March 2, 2009

    Hi guys:

    I don’t have time to follow all of this, but I think its really neat that you folks are debating these issues so openly. I guess I’m an ACC eco freak but its cool (sorry for the pun) that skeptics can post here and have their say. Here’s to hoping you guys are right (although I worry you’re not) and to me buying the drinks in 2020 when we’re all laughing at the ACC hypothesis. Or here’s to you buying the drinks if you turn out wrong. I’ll need the consolation for being correct.

    Skip

  28. #28 Eli Rabett
    July 1, 2009

    One of the saddest things is how people dig in and refuse to recognize the obvious. Even in the 1990s (and frankly before) humans responsibility for the rise in CO2 over the last 150 or so years was nailed down hard. Jan Schloerer wrote a nice FAQ on this, last updated in 1997. If anything, the evidence since then has gotten even stronger and still you get deep denial from a few. Go there and read the FAQ.

    As to the rest of Paul’s statement,

    a) it has been ~39 years since 1970, not 20,
    b) there are other things that force the climate, including volcanoes and aerosols. When you put it all together, you get an excellent match to how temperature has varied in the past century/

  29. #29 Jack
    August 14, 2009

    This whole discussion reminds me of a young colleague I worked with at MIT who won a grant to predict ocean shipping lane traffic by 2050. They gave him a year to do the research and write up the paper, but he kept screwing around and screwing around, and I kept bugging him about this until he turned to me about a month before the report was due and said, “Look, I’ll just do some straight-lining and adjust and tweak it here and there for known upcoming events and, if I’m really off in 2050 they can come get me.” This is apparently how it’s done in some parts of forecasting in academia – you pick a time horizon far enough in the future that it would be hard to prove you wrong.

    Same with this global warming stuff or any other religious predictions – if I’m wrong, just come find me. In the meantime, I’ll keep filling out grant applications and feeding at the trough of the taxpayers. It’s funny how data presented as counterexamples can be dismissed as too short-run or too anecdotal.

    I’ll ask you what I asked my students when we discussed how to construct theories and models: What sort of counterexamples and proofs do you need before you’re willing to back off and admit that your model does not work to predict future events? To be a scientific theory it must be “falsifiable” by counterexamples and data, so what do we need to counter the theories you’re propounding here? Specifically, the theory that human behavior is the primary cause of the rising temps problem, and that human bahavior, if changed, can solve the problem. This should be simple enough. I hope enough people are checking in on this board to see this recent activity.

  30. #30 coby
    August 14, 2009

    I see. Jack has idiots for friends, so everyone must be an idiot. Impressive line of reasoning.

    Now how about reading the article and trying to say something intelligent?