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Climate skeptics, deniers, hawks, and True Believers

Lots of accusations are flying around in the climate change debate. People who believe in anthropogenic (human-caused) climate change are accused of practicing religion, not science. People who don’t are called “deniers”, which some of them think is an attempt to draw a moral link with holocaust deniers. Al Gore referred to Sarah Palin as a “climate change denier,” and Palin immediately responded that she believes the climate changes, she just doesn’t think the level of greenhouse gases in the atmosphere has anything to do with it. What’s the right word to use for people like her? And yes, we do need some terminology if we want to be able to discuss the climate change debate!

In a recent blog entry about Climategate I used the term “climate change skeptics” to refer to people who are convinced that the climate effect of trebling or quadrupling the concentration of carbon dioxide in the atmosphere will be small or nonexistent. I used that term instead of “denier” because I’m not trying to pick a fight by using a term that some people feel is morally loaded. But the term “skeptic” isn’t right either, at least for some of these people. A skeptic is someone who isn’t convinced that something is true; that’s not the same as being completely convinced that the thing is not true.

Maybe we should start characterizing people by a single number, as follows. What probability do you assign to the following statement: increasing the atmospheric carbon dioxide concentration above 800 ppm will change the global average surface temperature by more than 2.5 degrees C (4.5 F)? This would imply a climate sensitivity somewhat below the extreme low end of what the Intergovernmental Panel on Climate Change says is credible. (The standard way of looking at climate sensitivity is to quantify the effect of doubling the pre-industrial carbon dioxide concentration, but that number is only relevant when you scale it somehow to much higher concentrations, since we are going to blow way past a mere doubling. I’ve chosen 800ppm, which is a bit less than triple the pre-industrial level. It’s likely that we’re going to zoom right past 800ppm, too).

This single “subjective probability” wouldn’t capture all of the variation in what people believe — two people with the same probability might differ enormously on what they think the response should be (if any); what they think the most likely temperature increase would be at that concentration; whether they think the biggest problems, if that temperature increase occurs, will be related to sea level rise or droughts or storms or floods; and so on. But at least using a number would avoid the pitfalls of having to choose terms — “denier”, “true believer”, and so on — that raise people’s hackles.

I’m not really serious about getting everyone to quote a number, I know it’s not possible: people aren’t going to talk about “0.1 percenters” instead of “denialists.” But I’m not at all convinced that it’s a bad idea, if we could make it happen. Just thinking about the issue, “what’s my number”, really does help me focus on my assessment of the evidence. This phenomenon will be familiar to anyone who has ever said “I’m sure” about such-and-such, and has had his bluff called by someone who says “OK, let’s bet on it, and if you’re really sure you should be wiling to give me 20:1 odds.”

If you believe the IPCC, your number would be…well, I don’t know exactly, perhaps a quantitative probability can be determined from their uncertainty range (I doubt it)… but considering the implied climate variability would be below their lowest credible estimate, someone who accepts the IPCC report completely would have a number somewhere over 95%, I think. Me, I’m a bit more skeptical, and I’d put the probability at 90%. I think there’s a 90% chance that 800ppm will be disastrous.

Everything above is, I hope, non-controversial. I don’t mean climate change is non-controversial, I mean that I think I have fairly characterized the IPCC position, Sarah Palin’s response to Al Gore, my personal assessment of the strength of evidence for anthropogenic climate change, and so on. I probably just ought to leave it at that, but I’m not going to, I’m going to go one step farther and tell you what I think is reasonable.

If someone says their number is 99.99% or higher, that is unreasonable. There is definitely more than 1 chance in 10,000 that the scientists have it wrong and the effect of CO2 will be much less than they think. If you want to say that people with this level of certainty are practicing religion rather than science, you’ll get no argument from me.

If someone says their number is 99.9%…well, would they _really_ offer 1000:1 odds? I don’t think this level of certainty is justified by the science, and in fact I would take this bet: I’d put $1000 on the long side, with a chance to win $1,000,000. This isn’t anything like the crazy level of certainty of a 99.99 percenter — hey, they’re allowing 10 times as big a chance of being wrong! — but it’s pretty far out there. I’d call it unreasonable, but not crazy.

99% is a reasonable number. So is my number of 90%. I think even 10% might be a reasonable number. Once you get below that, you’re in “pretty far out there” territory, the skeptical counterpart of the 99.9 percenter.

And, just as I think that lopping off a factor of 10 in the probability of error by going from 99.9% to 99.99% takes you from “pretty far out there” to “completely unreasonable” on the high side, I think lopping off a factor of 10 by going from 10% to 1% on the low side takes you from “pretty far out there” to “unreasonable.” If you really think there is less than a 1% chance that 800ppm of CO2 will have a major climate effect, I think you’re practicing religion, not science.

If I wouldn’t find a very low climate sensitivity shocking — I’m allowing a 10% chance — then should I be shocked to find that other people are completely convinced the climate sensitivity is very low? The answer is Yes. As with Andrew’s musings about the probability that the world’s greatest boxer will beat the world’s greatest wrestler, there are some subtleties in thinking about this kind of thing. The strength of the evidence is heavily on the side of climate sensitivity not being extremely low. It’s one thing to not allow yourself to be fully convinced by the evidence; it’s another to discount the evidence altogether.

I invite comments about this, of course. But I have one request: along with your comment, state your number. I think it’ll be fun. I also think that you will find that, if you take this exercise seriously, it makes you think hard about what you really think about the strength of the evidence, pro and con, for anthropogenic climate change.

47 Comments

  1. "Palin immediately responded that she believes the climate changes, she just doesn't think the level of greenhouse gases in the atmosphere has anything to do with it. What's the right word to use for people like her?"

    I think non-expert is probably the best term.

    Other than subject matter experts, general epistemology experts, I'm not sure the value of other people's thoughts, except to mitigate their potential for heckling and other forms of subverting expert consensus.

  2. Oh, and my number is 90% too, since you seemed to do the hard and careful work and I don't have the time (and probably not the competency).

  3. A non says:

    65%. No further comments.

  4. Pat says:

    I had to read one article describing those pimping the East Anglia "controversy" as "skeptics" three times before I realized who they were talking about. To me, a skeptic is someone who demands repeatable evidence of things like homeopathy, astrology, and gravity.

    So for god's sake don't ruin "skeptic." (Ha ha.) The word has a long and storied partnership with rational thought and the scientific method.

  5. harlan.myopenid.com says:

    Now that you've got a probability, you can start looking at utility. How much money would you spend to prevent the worst case scenario? Say, by 2075, New Orleans, most of Florida, and Manhattan uninhabitable, the price of food doubling, and 50% higher taxes to pay for more frequent wars, more frequent hurricanes, etc. You might well be willing to pay $10,000/year to prevent that scenario, especially if you have property in Manhattan! Now, what's the likely hit to your income if a carbon tax is used to shift energy to solar/wind/nukes? A few percent less, perhaps. Depending on your income, the expected value of the radical climate policy might well be better than the expected value of business as usual, even at only a 10% likelihood!

    It's insurance. Investment to prevent climate change is an insurance policy to mitigate a possible catastrophe down the road.

  6. BrendanH says:

    The complaint about "denial" implying holocaust denial is merely evidence of a persecution complex. The implication is more in the vein of "I'm not an alcoholic, I could give up any time I choose".

    John Quiggin wanted to go one further: skeptic -> denialist-> delusionist.

    As for my number, 80 to 90%, and I would endorse what Harlan says: the potential downside is bad enough to justify insurance even in the face of uncertainty.

  7. Phil says:

    Hey, everyone, I'm glad to see the comments, but don't forget to state your number! (Mine is 90%)

  8. Manoel Galdino says:

    I think that, conditional on actual technology we have and all information gathered, the probability is around 95%. And if you asked me for a bet, well, I would accept it as long as there were perfect markets, I mean, I could do some hedge in future markets if they existed.

    Actually, it would be nice to se politicians betting their future income (say, 20 years in the future) based on some policy recommendation of them.

  9. Jonathan says:

    20%

  10. Oriel boy says:

    Phil, where'd you get this from:

    "It's likely that we're going to zoom right past 800ppm, too"

    ?

  11. Oriel bo says:

    Oh, and my number is 95%. Just to piss off Andrew.

  12. efrique says:

    The way I look at it is that even if my probability is low end, probability isn't
    everything I need to look at – it's the costs
    associated with the two error types.

    The costs associated with radical attempts
    to reign in carbon and other emissions are
    very high. But the potential** costs ) of not
    acting at all seem astronomically bigger.

    **(those I'd give some non-vanishingly-small chance of happening, which in my ignorance, is
    probably a fair bit of what is mooted as possible)

    That's part of what worries me with the skeptics (and I hate the term – many of the people covered by the label are completely unskeptical about any claims made by the side they're on) – they seem to be playing pretty fast and loose with my grandchildren's lives, and if they're wrong, well, it won't cost the skeptics at all.

    Will it be like the skeptics associated with the fishing industry in Canada, where the scientists calling for much stricter catch limits were treated much like climate scientists are getting now (their science was denigrated, their evidence not conclusive enough, their conclusions not certain enough, their motives were questioned, they were accused of all sorts of stuff) – and once the fish stocks collapsed completely, the same scientists were blamed for having been insufficiently "certain", for couching their claims in scientifically cautious terms… attacked, in essence, for not being more successful in avoiding being attacked by people with a vested interest in questioning their recommendations.

  13. Anne says:

    Given past performance, I think I'd take twenty-to-one, and maybe hundred-to-one, odds that the IPCC's most conservative estimate is too conservative. So somewhere between 95% and 99%.

    There's a certain amount of betting that goes on in my group in astronomy, but oddly, most of it is in the form of "insurance" bets. For example, I found an object that looked like it might be the same as a known object. If so, that would be a big deal, a "missing link" between two classes of object. So one of our collaborators bet that it wasn't, figuring that that way either the object would be interesting and we'd get a paper in a journal with a one-word name, or at least he'd win the bet and get some free beer. (In the event, he lost the bet.)

    In this context, then, I'd prefer to make some kind of bet for the effects being severe – not that winning a beer or a little money would be much compensation for a large sea-level rise.

  14. Bill Mill says:

    Given that, according to Wikipedia, the IPCC concludes that "The probability that [AGW] is caused by natural climatic processes alone is less than 5%.", wouldn't a 99% estimate on your, much stronger, hypothesis be outrageously high? (Assuming 99% that AGW is occurring, ~90% that it's due to man, and probably 33% on your hypothesis presented at the top.

    (Do note: I understand my information is from wiki, and I'd love to see someone correct it if it's wrong.)

  15. Ian says:

    From what you wrote above, I assume you're talking about the equilibrium response to 800ppm, rather than the response in progress at a certain arbitrary future time (e.g., 2100). Although the fact that you're confident of a value below the (conservative) bottom of the IPCC range makes me wonder if you mean something else…

    Assuming you're talking about equilibrium response, I'll easily go with 99.5% .

  16. Kevembuangga says:

    we do need some terminology if we want to be able to discuss the climate change debate!

    Monkeys seem to fit the bill for all sides!
    Seriously, who cares for evidence or intellectual honesty as long as "we" win!
    Not too sure if there can be any "Science" about anything as soon as entrenched interests are at stake.

  17. David says:

    AS I don't believe there is any great scientific conspiracy going on, I interpret the question in terms of how much faith I put in the methods used to create the IPCC report. At 800ppm, the 90% temperature change interval they provide looks to be about +3C – +7C. Your 90% doesn't make you much of a skeptic at all. I'd be 80% because I don't trust models much… I think anyone putting less than 25% on that probability without having an intimate knowledge of the subject would be unreasonable.

  18. Andrew says:

    2008's Average Global Temperature was pegged by the met office at 14.3 °C

    If you're asking what are the odds that within a year of hitting 800 ppm CO2 that the number will climb to 16.8 °C, then I would put my number at 20.

    If you put the number up to the high end of the IPCC's Range, bringing the temp to more than 21°C, then I would put my number at 5 or less.

    The Jurassic: 1950 ppm, 16.5 °C
    The Silurian: 4500 ppm, 17 °C
    The Cambrian: 4500 ppm, 21 °C
    but then we see periods like:
    The Paleogene: 500 ppm, 18 °C

    CO2 doesn't appear to have ever been the driving factor in the climate of the past. It's always lagged by ~1000 years and has never been able to sustain a warmer system (temperature drops always occurred before CO2 level drops).

    This is a fantastic post, btw, and you've won me as a subscriber.

  19. Ian says:

    @Andrew said: "what are the odds that within a year of hitting 800 ppm CO2 that the number will climb to 16.8 °C"

    No chance of that at all, even if you could somehow get to 800ppm within a year's time. Is that the question we're supposed to be answering – climate response to new CO2 after a year? Everyone seems to be picking different "deadlines," probably without realizing it.

    also, "CO2 doesn't appear to have ever been *the* driving factor in the climate of the past."

    Right – but I've never heard anyone claim that it was. Why do you mention this?

  20. Oriel boy says:

    @Andrew:

    Your data looks reasonable, but your conclusion from it is wrong:

    http://www.skepticalscience.com/CO2-has-been-high

    http://www.realclimate.org/index.php/archives/200

  21. This ends up being tricky for a few reasons. First, the current level looks to be around 385 ppm [http://www.esrl.noaa.gov/gmd/ccgg/trends/], so I am being asked what would happen if carbon dioxide doubled. I’m going to first put out the ‘correlation is not causation’ probability. Notice the keyword in the statement “increasing the atmospheric carbon dioxide concentration above 800 ppm will change the global average surface temperature by more than 2.5 degrees C (4.5 F)?” is increasing, so causality must first be established. I’m going to put the causation probability at 50%, since I’m not much of an expert in climate science.
    Given that probability, I must then assign a probability of linearness. After all, if the carbon dioxide causality relationship to temperature is logarithmic, a doubling may have minimal effect on temperature. Then again, it might have a huge effect if it is exponential. I’m going to put a 99% probability on it being logarithmic [http://www.ipcc.ch/ipccreports/tar/wg1/044.htm] (although knowing the coefficients of the logarithmic relationship would be nice, I don’t trust others for them)..
    Carbon dioxide is not the only greenhouse gas, it accounts for [9-26% of warming] [http://en.wikipedia.org/wiki/Greenhouse_gas]. I’ve heard lower probabilities elsewhere, so I’m putting a 10% probability that Wikipedia is correct (since I cannot find direct concentrations of gasses, only gasses by contribution to global warming, and I think a religious cult of Al Gore put in faulty numbers), and a 90% probability that the real number is at most 5%.
    And, since the warmest it ever gets here in Montana is around 100 degrees F, a 5 degree increase would be 5%. Actually, that’s not fair, the mean temperature is closer to 50 degrees F, (yes the scales make no sense), so that’s a 10% increase. Since CO2 accounts for 5% of temperature increase, that means it would have to be twice the change.
    Using the Daniel Kahneman model of combining subjective probabilities in an irrational manner, that gives a .1% chance increasing carbon dioxide concentration to 800 ppm causes a temperature increase of 5 degrees Fahrenheit. My economic model also says that will result in more than a doubling of human productivity, which means future humanity will be much richer, and able to solve any climate related problems with vastly increased resources.

  22. tgrass says:

    efrique makes a solid point. Declaring the probability of AGW alone is not sufficient. Ultimately what we are after is someone's assessment of the Expected Value. Consequently we need their determination of costs: the benefits of not doing anything, and the costs of the consequences.

    I'd like to see people's EVs then. Much more telling.

  23. Ed says:

    There is a term I came across in an old (1970s?) political science text, which I would love to see revised, called "brass n' muck".

    This goes back to an English saying called "where there's muck, there's brass". In England, when restrictions on pollution were first proposed, apparently many people who lived in heavily polluted industrialized areas opposed them because they thought the restrictions would destroy their local economy by putting the heavily polluting industries out of business. The idea was that pollution was essential to create wealth.

    I have at least one friend who fits in with this mentality. There are climate change "sceptics" who, if the theories behind climate change were 100% confirmed tomorrow by Jesus, would still opposed measures to curb it because they think they would lead to no economic growth, and economic growth is more important. There are a few internet commentators who openly argue this, but I think people who try to hide behind "scepticism" are more common.

    There is a mirror image among environmentalists for people who want curbs on industrial activity for reasons that have nothing to do with climate change, but have seized on the controversy to push their agenda. My point is that I think the number of people who actually care about the science being correct is much lower than you think.

    There is actually an environmentalist position, I've seen it on the blog "counterpunch" but not elsewhere, that holds that environmentalism has a strong enough case without climate change and the theories behind climate change are so unsubstantiated that they could wind up discrediting the whole movement. This might be called "environmentalist climate change sceptic", I would think of a better name but we are dealing with a really small group. Its sort of like people geniuinely agreeing with free trade but opposing the actual free trade treaties.

    There are also the more numerous environentalists who are alarmed by climate change but view the Copenhagen summit as a public relations exercise.

    But I think its useful to make the distinction between genuine sceptics, people who really could be convinced that action to prevent or mitigate climate change is needed if they had stronger data, and the more ideological types. I think genuine sceptics tend to be a very small minority.

  24. marcel says:

    Will it be like the skeptics associated with the fishing industry in Canada, where the scientists calling for much stricter catch limits were treated much like climate scientists are getting now (their science was denigrated, their evidence not conclusive enough, their conclusions not certain enough, their motives were questioned, they were accused of all sorts of stuff) – and once the fish stocks collapsed completely, the same scientists were blamed for having been insufficiently "certain", for couching their claims in scientifically cautious terms… attacked, in essence, for not being more successful in avoiding being attacked by people with a vested interest in questioning their recommendations.

    There was a scene in "The Last King of Scotland" that this reminds me of. The protagonist, Nick Garrigan, a young Scottish doctor, finds himself an advisor to Idi Amin in the early days of his rule and recommends an inconvenient course of action as a way of avoiding pissing off Western governments. Amin ignores him, the result is as expected, and Amin blames the Garrigan. When he protests, Amin responds in all earnestness that it was Garrigan's fault for failing to persuade him.

  25. I don't have a number. I wonder how many people who do provide a number (or their analogues in the larger discussion) have examined the data for themselves?

    I have listened to any number of people offer rather strong opinions on this subject, despite receiving all of their information from secondary or tertiary sources. Though I think a reasonable stab at a probability such as you describe could be made subjectively by weighing the "experts", I worry that this is becoming a game of "argumentum ad verecundiam" (argument by "celebrity endorsement").

  26. jonathan says:

    Specifically with regard to Palin, remember that she is from and was governor of a major oil & gas producing state and thus she personally has a huge stake in avoiding any policy that may hurt oil & gas production. So I would call her a politician in this instance because she lies and distorts actual facts to protect her industry.

  27. anon says:

    Thanks for these posts, Phil.

    @Will 12/11 3:56:
    I have, and for the purposes of this post looked at the discussion of CO2 equilibrium in the IPCC summary report since Phil cited it.

    I agree with your point that the majority of people debating AGW probably get their opinions from sound bites and talking points gleaned from trusted entertainment/media/political personalities and bloggers (this is what you mean, yes?). But isn't this true of any politicized issue (esp. if highly complex)? I think an exercise like this is far more productive than the typical "argumentum ad hominem" we're used to.

    Anyway, my gut says 99.99, but I'll go with 95%.

  28. Andrew says:

    @Ian "No chance of that at all, even if you could somehow get to 800ppm within a year's time. Is that the question we're supposed to be answering – climate response to new CO2 after a year?"

    I'm saying by the time CO2 hits 800ppm, not we make the ppm 800 tomorrow and wait a year.

    Right – but I've never heard anyone claim that it was. Why do you mention this?"

    Because people are claiming that CO2 is the dominant force in climate change today. I think it's relevant to say that since it's never been the dominant force in the past, that it makes sense that it shouldn't be the dominant force today.

    @Oriel: RC needs to be taken with a grain of salt.

    That RC article chooses not to quote the more recent studies that have much higher resolution regarding the CO2 lag. In the past, factor X causes 800-2500 years of warming.

    Then CO2 and temperature rise together.

    Finally, factor Y causes temp to fall while CO2 continues to rise for 800-2500 years before it starts to fall. (CO2 was impotent to prevent this cooling). It looks more like temperature drives CO2 levels, not the other way around.

    Without any feedbacks, a doubling of CO2 (which amounts to a forcing of 3.7 W/m2) and the Stefan- Boltzmann equation gives us 0.6833 C degrees warming, which is easy to calculate and is undisputed.

    The remaining uncertainty is due entirely to feedbacks in the system. 80s and up think CO2 feeback will be positive, the 20s and under think CO2 feedback will not occur or will be negative (which it appears to have been in the past).

  29. anon wrote: "I have, and for the purposes of this post looked at the discussion of CO2 equilibrium in the IPCC summary report since Phil cited it."

    Is the raw data available publicly? I was unable to locate it on the IPCC summary. Where would one find such raw data?

  30. @jonathon:

    I think her big sin is lack of technocratic competence, not interest group capture, and making the message noisy is unhelpful.

  31. anon says:

    @Will:
    Gee whiz, you mean like, from scientists and data centers – like, say, Hadley? So you can do the science yourself? And I thought you were just saying that people don't try to make an informed decision so any attempt at assessment of what scientists present is pointless.

  32. Dano says:

    Is the raw data available publicly? I was unable to locate it on the IPCC summary. Where would one find such raw data?

    Yes.

    Or create your own raw data and work out the equilibrium equations. You know: the ones you got in radiative physics in Uni.

    Or you can get the data from the CRU-NOAA websites so you can work out the equations.

    Let us know what you get. Let us know if it is close to Charney sensitivity.

    Best,

    D

  33. PI says:

    Andrew,

    "I think it's relevant to say that since [CO2 has] never been the dominant force [in climate change] in the past,"

    That is a bold claim. How do you reconcile it with the Paleocene-Eocene Thermal Maximum and other hyperthermal events?

    "that it makes sense that it shouldn't be the dominant force today."

    That is failed logic. It only makes sense if you're comparing past events which are similar in every way to current (and future) events. When was the last time there was a externally (non-climatically) driven rapid input of 100s to 1000s of ppm CO2 over hundreds of years? How do you know what that will do to the climate? What is your past analogue to that which tells you what would happen? Why are you sure that kind of CO2 input would not have been a "dominant force in climate change" had it happened (especially in light of the previously mentioned hyperthermal events when it quite possibly did happen)?

    The relevant question is, what does the past tell us about the climate sensitivity to CO2, and what does this imply about future climate change under projected CO2 emissions?

    "the 20s and under think CO2 feedback will not occur or will be negative (which it appears to have been in the past)."

    Another bold claim. What is the basis for it? There exist paleoclimate estimates from the Last Glacial Maximum, Phanerozoic, PETM, etc. which all find positive feedbacks within the canonical IPCC range.

  34. PI says:

    Cody,

    There are some serious problems with your calculations.

    "Carbon dioxide is not the only greenhouse gas, it accounts for [9-26% of warming] <a href="http://[http://en.wikipedia.org/wiki/Greenhouse_gas%5D.&quot;” target=”_blank”>[http://en.wikipedia.org/wiki/Greenhouse_gas]."

    This is a largely irrelevant figure. The relevant question is what fraction of the change in greenhouse warming, in addition to the baseline greenhouse effect, is attributable to changes in carbon dioxide.

    Analogy: suppose non-CO2 GHGs contribute 30 degrees of greenhouse warming, and CO2 contributes, say, 1 degree. Then humans increase CO2 so it contributes 2 degrees, and all the other GHGs stay the same. CO2 will be responsible for all of the 1 degree warming, despite the fact that CO2 is a small contribution to the total greenhouse effect.

    (In reality, the increase in CO2 will also cause an increase in water vapor which is a GHG, so there is an amplifying feedback here which can ultimately be traced back to CO2.)

    "since I cannot find direct concentrations of gasses, only gasses by contribution to global warming, and I think a religious cult of Al Gore put in faulty numbers),"

    Oh come on.

    "And, since the warmest it ever gets here in Montana is around 100 degrees F, a 5 degree increase would be 5%."

    That's a physically meaningless comparison, since it depends on the arbitrary choice of zero in your temperature measurement system. (In Celsius, that would be a 2.8 increase relative to 37.8 degrees, or a 7% increase.) You need to make comparisons on an absolute temperature scale.

    I confess I can't even understand what your calculation is supposed to demonstrate. But here is what is being claimed by climate scientists:

    A 100 ppm increase in CO2 leads to about 1.6 watts per square meter of radiative forcing (top of atmosphere), assuming a logarithmic concentration-forcing relationship. By comparison, this is about 0.5% of the power contained in the solar radiation intercepted by the Earth (top of atmosphere).

    As a result, the surface temperature of the Earth is expected to eventually increase by about 0.5 degrees C, which is a 0.2% increase in the Earth's surface temperature (~288 Kelvins). If you count the positive feedbacks which exist in the climate system, this is estimated to increase to more like 1.3 C, or a 0.5% increase in the Earth's surface temperature. (On the high end of the IPCC range, it's 2 C or 0.7% increase.)

    So, you have about a 0.5% change in radiative forcing relative to what the Sun gives us, which results in a 0.2-0.7% increase in planetary surface temperature. The only controversial part is whether it's closer to 0.2% or 0.7%.

    "Actually, that’s not fair, the mean temperature is closer to 50 degrees F, (yes the scales make no sense), so that’s a 10% increase. Since CO2 accounts for 5% of temperature increase,"

    As pointed out above, the fractional contribution of CO2 to the total greenhouse effect is not the same as the contribution of changes in CO2 to changes in temperature. The latter is the relevant figure.

    "Using the Daniel Kahneman model of combining subjective probabilities in an irrational manner,"

    … by severe double-counting. For instance, you started out with a 50% prior probability that the basic claim was wrong, and then you tacked on additional odds that the claim is wrong for specific reasons. These are not independent. (And I don't know how you arrive at 0.1% from that anyway.)

    "My economic model also says that will result in more than a doubling of human productivity, which means future humanity will be much richer, and able to solve any climate related problems with vastly increased resources."

    What

  35. PI says:

    Cody,

    The last part got cut off.

    "My economic model also says that will result in more than a doubling of human productivity, which means future humanity will be much richer, and able to solve any climate related problems with vastly increased resources."

    What economic model are you using to estimate climate damages? (Though I suppose it's irrelevant if you have a very low estimate of likely climate change …) And what does your economic say about human productivity and wealth under a proposed climate mitigation policy?

  36. Will Dwinnell says:

    anon wrote: "Gee whiz, you mean like, from scientists and data centers – like, say, Hadley? So you can do the science yourself?"

    Your comment is not constructive. I am seeking information on where to find the data since, yes, I would be interested in looking at it myself. Can anyone provide a substantive answer to my question, perhaps a link to data on-line?

    anon wrote: "And I thought you were just saying that people don't try to make an informed decision so any attempt at assessment of what scientists present is pointless."

    I still assert that most people do not examine the primary research, much less the raw data, so it is unclear to me why any value should be assigned to their opinions. But I don't understand what your comment has to do with my interest in obtaining data.

  37. For others interested in learning more about this subject, and at least one possible source of data, I have come across this (which I am still studying):

    http://iowahawk.typepad.com/iowahawk/2009/12/fabl

  38. PI says:

    Will,

    What raw data are you looking for, specifically?

  39. .4 ≥ 2.5 C, .1 ≥ 5 C. Frankly, I am skeptical that the feedback will be positive, but I also think there is a reasonable P that the rate at which the ocean absorbs CO2 will drop dramatically in the near future. So I see a pretty long right tail.

    There is also the question of what moderate warming would do to life on this planet. It is not unreasonable to assume the effects would be largely positive — as in the medieval warming period (my interpretation of the evidence suggests that it was warmer than now, at least in Europe, although that is matter of some debate). Moreover, the last two decades have been quite warm by historical standards and, globally speaking, this has been a golden era — never in the past have so many people climbed out of abject poverty nor has the percentage of the world's population living on less than 2$ a day ever been as low.

    Nevertheless, given the uncertain risks, the manifold benefits of reducing dependence on fossil fuels, the relatively moderate cost of abating carbon emissions, this seems like a perfectly sensible insurance policy.

    What follows goes off on a tangent, but I have seen a lot of speculation about why it is that folks of my generation (over 65) are much more skeptical of AGW than the rest of you. Most question our rationality or our world view. Well, maybe. But I have also noted that many of my coevals observe that it doesn't seem warmer (I agree; it doesn't, but I trust meteorological records more than my memory) and that they just don't believe weathermen (even though they may spend hours each week watching the weather channel, maybe because they spend so much time watching the weather channel) — if weathermen cannot get their predictions right 2 days out why should we trust them to get it right 90 years down the road? OK, I understand the difference between a trend and stochastic variation, but the relevance of this distinction isn't universally obvious. Anyway, this generational difference is interesting and any enlightenment would be appreciated.

  40. anon says:

    @Will:

    Gosh. My bad. A Google search for "climate data" looks like it should be helpful for you. Then again, I'm no data miner or anything. And, since you have some data to study now, you'll be able to participate in Phil's exercise. Looking forward to your contribution.

    Glad we both agree that people shouldn't just recite what they hear on the radio, read on blogs, etc.

  41. tgrass says:

    He writes that those claiming 99.99% are crazy, while those making a 1000:1 wager are merely unreasonable. In the end though, there is no way to conclude the wager without allowing emissions to continue unregulated for decades. Thus the wager is unreal. With no consequences, the risk can be infinite. In fact, some pundits talk as if they'd claim 100% that there is no warming.

    Might there be a way to impute a realistic probability to some third party by their behavior?

    If you were 99.99% sure warming was not anthropogenic, how would you hedge against political action restricting carbon emissions?

  42. Hopefully Anonymous says:

    "Moreover, the last two decades have been quite warm by historical standards and, globally speaking, this has been a golden era — never in the past have so many people climbed out of abject poverty nor has the percentage of the world's population living on less than 2$ a day ever been as low."

    Good reframe. Perhaps we shoul be thinking about optimum temperature rather than simply correcting AGW.

  43. Phil says:

    Fred,
    Your distribution is pretty similar to mine, I think.

    As far as whether a warmer world is better/worse/same as now…I've deliberately avoided discussing this issue, in this post and in subsequent ones, but now that we're way down in the comments I'll say what I think. If warming happened gradually, perhaps it would be OK (although I dunno, ocean acidification scares me). But really rapid change — 4C over the next 200 or 300 years, just to pick a number — has just got to be really bad, if it happens. Cities, reservoirs, canals and water pipelines…even human populations in general….they're all located where they are in part because of the current climate. It would be going too far to say that human infrastructure is highly optimized for the current climate, but it is at least somewhat optimized for the current climate, and will be badly non-optimal if sea level is 1.5m higher, and/or if rainfall patterns change a great deal, or if the deserts expand a lot.

    But all of this is separate from the question of whether AGW is happening.

  44. Phil, This series of blogs and the comments they have elicited are a model of the medium at its best. I thank you and Andrew.

  45. ChristianK says:

    When would we reach 800ppm when we would continue to produce exactly the same amount of CO2 per year that we are producing at the moment?

    The word skeptic today usually means people like James Randi who feel pretty certain about the fact that there no God and there no paranormal stuff.

    Real skeptics who don't believe that they know the truth like Nassim Taleb are much fewer and generally a classical skeptic like Nassim who happens to be a theist isn't what most people associate with the term today.

  46. Justin says:

    Here's the problem: why do the commenters on this website think that they're more qualified to interpret the scientific data than… the scientists? Asking everyone for their "number" just encourages the idea that the general public ought to form its opinion based only partly on scientific consensus, and mostly on however they feel that particular day. If I say I'm 20%, why on earth should that matter? The point is that the people that know what they're talking about (and the world leaders of 193 countries) are all saying climate change is real, it's happening, it will happen, and it will likely be many times worse that we can even imagine.

  47. AE says:

    Justin, the idea that scientists in any discipline are the only ones qualified to evaluate their own output is ridiculous. What's more, its undemocratic — climate scientists need to be able to explain their conclusions well enough that the general public can grasp it and agree with it, or they should get out of the public policy business altogether. Sure, climate science is way more complex than other scientific issues bearing on policy. Sorry, but that's a bug, not a feature.

    And politicians in general have no better scientific understanding than unelected laypersons… why is their consensus informative at all?