tag:blogger.com,1999:blog-9959776.post2333053176215684326..comments2024-02-15T04:42:41.606+00:00Comments on James' Empty Blog: Roe and BakerJames Annanhttp://www.blogger.com/profile/04318741813895533700noreply@blogger.comBlogger24125tag:blogger.com,1999:blog-9959776.post-26710737312632985212007-11-07T12:53:00.000+00:002007-11-07T12:53:00.000+00:00Oh, I would start from pre-industrial, on the basi...Oh, I would start from pre-industrial, on the basis that we know the p-i temperature well enough to calculate S. Stabilising now and comparing to p-i would work just about as well (smaller signal, uncertainties are relatively larger) but that ignores the possibility of nonlinearity in the response out to 2xCO2 (not that I expect that to be large). Settling on 2xCO2 is largely historical of course...<BR/><BR/>I also agree we would be able to make a good estimate of S well in advance of the actual equilibration - I think we already have a pretty good estimate!James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-63570789944241871222007-11-06T16:52:00.000+00:002007-11-06T16:52:00.000+00:00>"let's consider the following definition of S, wh...>"let's consider the following definition of S, which is based on Morgan and Keith's 1995 survey: S is defined to be the observed global temperature rise, measured as a 30-year average, 200 years after the CO2 level is doubled from the pre-industrial level and then held fixed (with other anthropogenic forcings unchanged)."<BR/><BR/>For sensitivity from *now*, presumably this creates a problem and it is necessary to hold the GHG level fixed for 200 years then double the CO2 level then keep them fixed for 200 years. If you didn't do this hold steady first you would count the committed warming twice. <BR/><BR/>If we knew what the committed warming was we would have a much better idea of the sensitivity and the doubling part would be less needed to narrow down the sensitivity. <BR/><BR/>So if you want to operationally define it then why not just say stabilise CO2 levels as soon as possible. After 50 years at stable CO2 level, estimate the equilibrium temperature with best models at that time and compare to preindustrial temperature. Finally adjust for the change in CO2 not being a doubling. There is more uncertainty with doing this than the full 500+year method but after 500 years I doubt we would be that interested in the sensitivity to want to go to that much trouble to find out.<BR/><BR/><BR/>Any comments on my previous point about the need to try to shift the focus to say we also have to look at what has to happen in the future before we know what sensitivity is as well as your focus on what has happened to get some idea of the progress made?crandleshttps://www.blogger.com/profile/15181530527401007161noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-5353667963884723572007-11-03T01:53:00.000+00:002007-11-03T01:53:00.000+00:00Thanks, I hadn't seen that paper. It looks like my...Thanks, I hadn't seen that paper. It looks like my assertion was basically right - initial conditions have very little effect, so even if this is treated as an "intrinsic uncertainty" in climate sensitivity, it is not a significant one.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-32035763614722742302007-11-02T13:31:00.000+00:002007-11-02T13:31:00.000+00:00It might be table 6 of the supplementary informati...It might be table 6 of the supplementary information that you want.<BR/><BR/><A HREF="http://tinyurl.com/33t869" REL="nofollow">Supp info</A>crandleshttps://www.blogger.com/profile/15181530527401007161noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-70202309818506307072007-11-02T12:41:00.000+00:002007-11-02T12:41:00.000+00:00For presentation of those results you want Knight ...For presentation of those results you want <A HREF="http://www.climateprediction.net/science/pubs/PNAS_knightetal_2007.pdf" REL="nofollow">Knight et al<BR/>PNAS July 07</A><BR/><BR/>I wrote to Sylvia mid July with a few questions. I saw her recently and she said it was still in her in-tray.<BR/><BR/>William has said he thinks a text file of the parameters and sensitivities should be available. At the time I knew Knight et al was in preparation and thought it might be reasonable for them to withhold it to allow them a stab at this before making the data available. Now it is published I agree it should be available and asked for it. So if anyone else wants to add their voices to a call for this then feel free to ask.<BR/><BR/>(Sorry about going off on a ranting tangent like that.)<BR/><BR/>William recently mentioned the known ic related cold equator models (ocean ice west of ecuador) that occur with some slabs. We have seen large divergences just from initial conditions in this way but this is known to be unphysical.<BR/><BR/>I think there are others with quite a bit more than .1C difference for a year. With 30 year average, the differences each year could easily average more than .1C and average to less than .1C.<BR/><BR/>This is only a model rather than reality and the model may well not have enough natural variability - I don't recall seeing 1998 el nino size variation. (Well I have seen much larger but dismissed it as computing error.) But see the paper rather than relying on me.crandleshttps://www.blogger.com/profile/15181530527401007161noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-25019525576348545842007-11-02T09:41:00.000+00:002007-11-02T09:41:00.000+00:00Or are you saying it is only the 30 year global av...<I>Or are you saying it is only the 30 year global average temperature that is predictable so such cycles will average out down to your 0.1C uncertainty?</I><BR/><BR/>Yup, that's exactly my point.<BR/><BR/>CPDN did a whole lot of replicates (same parameters but different initial conditions) in their original experiment, didn't they? I don't recall any presentation of those results - do you know if they found these to give significant differences (other than perhaps the nonphysical crashes)?James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-51205257231181787952007-11-02T09:28:00.000+00:002007-11-02T09:28:00.000+00:00>"If it's just the current state of the atmosphere...>"If it's just the current state of the atmosphere then I don't believe it."<BR/><BR/>So are you saying that the state of the atmosphere cannot affect El Nino cycles even with 50 years to try? <BR/><BR/>Or are you saying it is only the 30 year global average temperature that is predictable so such cycles will average out down to your 0.1C uncertainty?<BR/><BR/>or something else?<BR/><BR/><BR/>>"I don't think you got my point."<BR/>I realise that I was talking about a completely different point to what you were saying.crandleshttps://www.blogger.com/profile/15181530527401007161noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-46511161891880721582007-11-02T07:47:00.000+00:002007-11-02T07:47:00.000+00:00Eli is a smart bunny, and generally close to the t...Eli is a smart bunny, and generally close to the truth. But after 200 years, the climate would be close to equilibrium (for global temp if not details such as ice sheets), unless S is very high. And when talking of "20 earths", what are the proposed differences between these earths? Ie, what is the distribution from which they are taken? If one allows different land fractions, atmospheric composition, orbital parameters etc...of course S will change. If it's just the current state of the atmosphere then I don't believe it.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-13360414942380980742007-11-02T02:54:00.000+00:002007-11-02T02:54:00.000+00:00Eric,Obviously the model (and initialisation) woul...Eric,<BR/><BR/>Obviously the model (and initialisation) would have to be essentially perfect :-)<BR/><BR/>My Lorenz models have always been deterministic, so any uncertainty in their outputs can only ever be epistemic. "Stochastic" inputs, when they are used, are (almost?) always really representing unknown processes, not "random" ones.<BR/><BR/>But this is perhaps an unnecessary distraction, because the issue is not whether there can ever be any truly "random" effect, but whether such random effects could be large enough to substantially affect the climate sensitivity. I don't believe it, and a vague comment about "chaos" does not support the hypothesis. Models are chaotic too, and show no such effect. In fact, as with Allen and Frame's "intelligent warming", there does not even seem to be a testable hypothesis associated with it.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-2259747347003813332007-11-02T02:43:00.000+00:002007-11-02T02:43:00.000+00:00Chris,I don't think you got my point. One complain...Chris,<BR/><BR/>I don't think you got my point. One complaint of the Bayesians is that "climate sensitivity" is a rather hidden parameter (either in the classical derivative form dT/dF, or the alternative of a true equilibrium), so it is hard to make a direct observation of the climate system that can be used to challenge predictions of such a theoretical construct. I'm just trying to side-step that objection by presenting everything in terms of a directly observable (operationally defined) version which is pretty much the same thing (it's not quite identical, but would be just as useful to policymakers). It is also more-or-less what modellers do to calculate the sensitivity of their models.<BR/><BR/>Hank,<BR/><BR/>In order to keep at 550pm someone might need to nuke a few nations...James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-14073995537620314772007-11-02T01:17:00.000+00:002007-11-02T01:17:00.000+00:00I think (ok dangerous ground) that there will be o...I think (ok dangerous ground) that there will be one climate sensitivity for this earth in any particular number of years and I think this is what JA is saying. However for a different number of years the cs will be different. (Of course given 20 earths we would have 20 answers) This may be my vision of a Baysean POV. From that standpoint there is a single correct climate sensitivity, however, it neglects measurement uncertainty. Of course, I could be pushing my luck hereEliRabetthttps://www.blogger.com/profile/07957002964638398767noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-15899726059412905422007-11-01T16:10:00.000+00:002007-11-01T16:10:00.000+00:00I'm guessing that this:> if we chose to do it and ...I'm guessing that this:<BR/><BR/>> if we chose to do it and weren't<BR/>> too bothered about killing a few<BR/>> people along the way<BR/><BR/>is meant as a reference to thinking about choices like this?:<BR/><BR/>http://www.sciam.com/article.cfm?articleID=76613503-E7F2-99DF-3E772052740833A2<BR/><BR/>"... In one setup, the choice was whether or not to push someone onto a railroad track to prevent a runaway train from killing five other people; in another, the choice was whether to flip a switch that would route the train from a track where it could strike five people to another track where it would kill only one...."<BR/><BR/>Either we kill some people now, in our own lifetimes, or we leave 'the train on the track headed toward the larger crowd' but it hits them after our lifetime and we don't actually see it happen? <BR/><BR/>Or, of course, a miracle ....Hank Robertshttps://www.blogger.com/profile/07521410755553979665noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-83299986009679263032007-11-01T15:51:00.000+00:002007-11-01T15:51:00.000+00:00James,When you wrote that ..."with a sufficiently ...James,<BR/><BR/>When you wrote that ..."with a sufficiently accurate model and observations, the temperature [Xmas day 50 years from now] really could in principle be predicted accurately," you can't have been serious, can you? What happened to Lorenz (not to mention just plain old stochastic noise? I realize this isn't entirely relevant to the point about the pdf of f, but it surely confuses things. Comments? <BR/><BR/>Eric Steig (RC)Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-9959776.post-76672095230353542007-11-01T13:11:00.000+00:002007-11-01T13:11:00.000+00:00You are not going to agree with this but I want to...You are not going to agree with this but I want to see why.<BR/><BR/>Your experiment involves 200 years of good climate observations versus having 30 years of good climate data. Obviously we cannot just take that 200 to 30 year ratio for at least 3 reasons.<BR/><BR/>1. There is considerable diminishing returns though the 200 year period.<BR/>2. We have thousands of years of paleo climate data but there is more uncertainty about the conditions at that time.<BR/>3. Your 200 years are specifically designed to measure sensitivity whereas the last 30 years have seen co2 levels rising at similar rates to the previous 30 years which makes it difficult to apportion temperature rises to which CO2 rises. To measure sensitivity accurately you need a sharp change and we haven't had that.<BR/><BR/>If I think 3 is by far the most important reason and completely unscientifically off the top of my head wildly estimate 10% of the reduction in range from 3K to .1K is due to the information in the last 30 years then we would expect .3K reduction in the range.<BR/><BR/>In fact, if the lower end has increased from 1.5K to 2K then we have seen a better reduction in range than my wild estimate would expect.<BR/><BR/>Why has this all occured at the low end of the range rather than some at the top end of the range? Well this is due to the reasons that Roe and Baker have detailed.<BR/><BR/>Thoughts?crandleshttps://www.blogger.com/profile/15181530527401007161noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-28754697416274852772007-11-01T13:04:00.000+00:002007-11-01T13:04:00.000+00:00Well, there is not really any advice for policymak...Well, there is not really any advice for policymakers, just some analysis of what others have published. I don't think it so clearly wrong as to be worth commenting on officially - and I also know there would be no chance of getting such a comment published, given how hard it is even in cases when there are clearly identifiable errors with significant consequences.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-72232999288214759442007-11-01T11:54:00.000+00:002007-11-01T11:54:00.000+00:00James wrote:"It's not really wrong so much as irre...James wrote:<BR/>"It's not really wrong so much as irrelevant."<BR/><BR/>Isn't it fair to say that their conclusion that <I>by definition</I> a long tail is inevitable wrong, in your opinion; and from a policy maker's perspective, isn't that important?<BR/><BR/>James wrote:<BR/>"I'm also optimistic that it will be largely ignored"<BR/><BR/>Maybe by the specialists, but it's certainly generated a lot of publicity, presumably because it got into <I>Science</I>.DaveRhttps://www.blogger.com/profile/03882184827847935285noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-11938166949581109912007-11-01T11:40:00.000+00:002007-11-01T11:40:00.000+00:00Gha! Never mind I just realised the mistake... sho...Gha! Never mind I just realised the mistake... should learn to think before I write :)Magnushttps://www.blogger.com/profile/01617272924116099306noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-53694235674077847412007-11-01T11:32:00.000+00:002007-11-01T11:32:00.000+00:00Ahh, never mind me :) I’ll blame it on the early m...Ahh, never mind me :) I’ll blame it on the early morning!<BR/><BR/>What about an increase in solar input ------> more water vapour-----> less ice-----> more forest? To small change I guess... but at least now I’m in the right ballpark?Magnushttps://www.blogger.com/profile/01617272924116099306noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-44523323611674314172007-11-01T10:41:00.000+00:002007-11-01T10:41:00.000+00:00Oh no, it had never crossed my mind. It's not real...Oh no, it had never crossed my mind. It's not really wrong so much as irrelevant. I'm also optimistic that it will be largely ignored, since from what I've heard, other people working in this area (apart than Allen and Frame, of course) are equally surprised that it was considered publishable.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-7679047678960192042007-11-01T10:16:00.000+00:002007-11-01T10:16:00.000+00:00James, will you be writing to Science about this?James, will you be writing to Science about this?DaveRhttps://www.blogger.com/profile/03882184827847935285noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-30483540167577854272007-11-01T09:55:00.000+00:002007-11-01T09:55:00.000+00:00Belette,Mostly I think it just indicates muddled t...Belette,<BR/><BR/>Mostly I think it just indicates muddled thinking. But if it is also used as a justification for some substantial "irreducible uncertainty" then it risks damaging the scientific process (and certainly damaging the credibility of this niche of climate science). I think it is also fundamental to Marty Weitzman's argument.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-8930989145644137112007-11-01T09:50:00.000+00:002007-11-01T09:50:00.000+00:00Magnus,All that could happen, but it's not releva...Magnus,<BR/><BR/>All that could happen, but it's not relevant to climate sensitivity which is specifically defined as the temp change while holding the forcing fixed at 2xCO2 (or temp change per unit forcing for the "gradient" definition). In the 200 year experiment I mention, we might need to devise a method for absorbing methane if the natural environment starts to emit it in larger quantities.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-26852395911967403582007-11-01T09:34:00.000+00:002007-11-01T09:34:00.000+00:00So... I'm curious as to how much the number-vs-pdf...So... I'm curious as to how much the number-vs-pdf bit matters. I'm inclinded to think that if people can't even agree on that, then the issue is very unclear, and we're back to mediaeval philosophers arguing about infinity without having first defined it.William M. Connolleyhttps://www.blogger.com/profile/05836299130680534926noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-66616511650995630042007-11-01T08:34:00.000+00:002007-11-01T08:34:00.000+00:00Maybe a bit naive but what if:Temperature rise met...Maybe a bit naive but what if:<BR/>Temperature rise methane production release from tundra / swamps -----> higher temperature different ocean circulation less CO2 uptake -----> hotter, --------> less CO2 uptake -----> change in circulation ------> ice sheets melts --------> hotter and so on... cold that not be a non linearity for certain T:s? (I guess you could change the order)<BR/><BR/>Or is that ruled out by proxidata?<BR/><BR/>Just a thought like...Magnushttps://www.blogger.com/profile/01617272924116099306noreply@blogger.com