tag:blogger.com,1999:blog-5337555368793819627.post1909362574597734526..comments2023-06-07T09:04:36.390-04:00Comments on More Grumbine Science: CO2 and temperature for 800,000 yearsRobert Grumbinehttp://www.blogger.com/profile/10783453972811796911noreply@blogger.comBlogger37125tag:blogger.com,1999:blog-5337555368793819627.post-72103767876968596442010-11-01T12:11:35.923-04:002010-11-01T12:11:35.923-04:00Hi, Robert. I hope your wrist is healing nicely.
...Hi, Robert. I hope your wrist is healing nicely.<br /><br />I previously posted this comment at Watts Up With That. You asked me to re-post it here, so here it is! (I changed a few words to try and improve clarity.)<br /><br />Hi, Robert. A few comments on your post.<br /><br />You state that your analysis of the ice-core record disproves two conjectures: 1) that the current CO2 rise is due to past temperature increases; and 2) that CO2 in the atmosphere can’t be affecting current temperatures. Your analysis is predicated on the fact that the modern rise of CO2 does not have an equivalent in the ice-core data and is much higher than anything seen in that record.<br /><br />There are other reasons to believe the current rise in CO2 is due to human influence, or that CO2 affects temperature to some (disputed) degree. However, CO2 levels from the ice-core data CANNOT be used in comparison with the CO2 levels in the modern era (i.e., the last half of the 20th century up until now). The reason for this is the “yardstick” for measuring temperature and CO2 levels from the ice-core data is VERY crude - much less precise than the annual Mauna Loa information. <br /><br />I’m assuming you used data from the Vostok ice core? As I recall, the precision for this data is 700 yrs, +/- 200. This is due to the very low rate of precipitation, and the long amount of time before the CO2 becomes “trapped” in the ice.<br /><br />So essentially, your analysis is using “smoothed” data, smoothed over 700 years. <br /><br />Trying to measure an annual effect using ice core data is kind of like trying to measure a person’s height using your car’s odometer. In other words, it is entirely possible that CO2 levels have had a much larger range in the past, and are simply smoothed out in the ice-core data. We would need a few hundred years' worth of data (at least!) from Mauna Loa, before we could say anything substantial in the comparison. (And, of course, that data would have to be normalized against future ice core data.)<br /><br />This mistake of comparing the crude precision of ice-core data with the high precision of modern measurements is made all the time, especially in the press. Al Gore’s presentation is a particularly well-known example. I'm surprised the issue doesn't come up more often.<br /><br />But if anyone else has some more information on this, I’d be glad to read it … I’m not an expert in ice-core data.<br /><br />Cheers.Tedsaidhttps://www.blogger.com/profile/12804766446627357544noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-68184817200358901642010-11-01T12:10:52.328-04:002010-11-01T12:10:52.328-04:00Hi, Robert. I hope your wrist is healing nicely.
...Hi, Robert. I hope your wrist is healing nicely.<br /><br />I previously posted this comment at Watts Up With That. You asked me to re-post it here, so here it is! (I changed a few words to try and improve clarity.)<br /><br />Hi, Robert. A few comments on your post.<br /><br />You state that your analysis of the ice-core record disproves two conjectures: 1) that the current CO2 rise is due to past temperature increases; and 2) that CO2 in the atmosphere can’t be affecting current temperatures. Your analysis is predicated on the fact that the modern rise of CO2 does not have an equivalent in the ice-core data and is much higher than anything seen in that record.<br /><br />There are other reasons to believe the current rise in CO2 is due to human influence, or that CO2 affects temperature to some (disputed) degree. However, CO2 levels from the ice-core data CANNOT be used in comparison with the CO2 levels in the modern era (i.e., the last half of the 20th century up until now). The reason for this is the “yardstick” for measuring temperature and CO2 levels from the ice-core data is VERY crude - much less precise than the annual Mauna Loa information. <br /><br />I’m assuming you used data from the Vostok ice core? As I recall, the precision for this data is 700 yrs, +/- 200. This is due to the very low rate of precipitation, and the long amount of time before the CO2 becomes “trapped” in the ice.<br /><br />So essentially, your analysis is using “smoothed” data, smoothed over 700 years. <br /><br />Trying to measure an annual effect using ice core data is kind of like trying to measure a person’s height using your car’s odometer. In other words, it is entirely possible that CO2 levels have had a much larger range in the past, and are simply smoothed out in the ice-core data. We would need a few hundred years' worth of data (at least!) from Mauna Loa, before we could say anything substantial in the comparison. (And, of course, that data would have to be normalized against future ice core data.)<br /><br />This mistake of comparing the crude precision of ice-core data with the high precision of modern measurements is made all the time, especially in the press. Al Gore’s presentation is a particularly well-known example. I'm surprised the issue doesn't come up more often.<br /><br />But if anyone else has some more information on this, I’d be glad to read it … I’m not an expert in ice-core data.<br /><br />Cheers.Tedsaidhttps://www.blogger.com/profile/12804766446627357544noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-42978246414302189812010-07-23T12:33:33.781-04:002010-07-23T12:33:33.781-04:00Absolutely. I encourage that. That's the rea...Absolutely. I encourage that. That's the reason for the 'project folder' tag -- all of those posts have ideas and/or data for you to try working with.Robert Grumbinehttps://www.blogger.com/profile/10783453972811796911noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-66896706805368925862010-07-23T04:13:10.067-04:002010-07-23T04:13:10.067-04:00i just wanted to play with the data myself .. many...i just wanted to play with the data myself .. many many thanks .. your reference was very helpful .. !!A bit losthttps://www.blogger.com/profile/15867892639378151577noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-58828164177790419012010-07-22T19:54:56.981-04:002010-07-22T19:54:56.981-04:00The numbers I used were from the spreadsheet at th...The numbers I used were from the spreadsheet at the BBC article I linked to -- http://news.bbc.co.uk/2/hi/in_depth/sci_tech/2009/copenhagen/8393855.stm<br /><br />These are not the most raw data you could get, however. They've already been analyzed to give you information at a regular spacing -- every 1000 years. To get closer to the raw data on ice cores, you want to visit the <a href="http://www.ngdc.noaa.gov/paleo/icecore/current.html" rel="nofollow">National Geophysical Data Center -- Ice Core</a>, for instance.Robert Grumbinehttps://www.blogger.com/profile/10783453972811796911noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-13368268790602104952010-07-22T18:36:43.465-04:002010-07-22T18:36:43.465-04:00more than a comment, i had a question. I was wonde...more than a comment, i had a question. I was wondering where one can obtain the raw data on climatic data, like for example what you used for your Figure. I understand that these data are published, but many of the sources I see do not provide any table of data, but just a figure. Given that someone painstakingly collected so much valuable data for over 800k years, I was wondering if the measured numbers are cataloged in some database .A bit losthttps://www.blogger.com/profile/15867892639378151577noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-54389233936127473092010-02-03T10:35:19.338-05:002010-02-03T10:35:19.338-05:00Anon:
Simply asserting things is not interesting. ...Anon:<br />Simply asserting things is not interesting. Asserting things that are false, or are irrelevant, is worse.<br /><br />Nobody here has said that CO2 will cause a runaway greenhouse. Your attack on that is, therefore, dishonest. I've actually never seen anybody, certainly nobody in a relevant science, say that the earth could have a runaway greenhouse. If you have seen a climate scientist say so, please post the link. <br /><br />You talk of 'magnetosphere strength' or the like as a concern for climate. But, again, without any scientific support.<br /><br />This is a science blog, and you seem unfamiliar with what that means. One thing it means is that we're concerned with what is in the science. It also means that if you make a claim about science, it should be supported. To that end, read the link policy.Robert Grumbinehttps://www.blogger.com/profile/10783453972811796911noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-26708787745884420902010-02-03T04:58:56.666-05:002010-02-03T04:58:56.666-05:00Why focusing on CO2 and AGW is silly.
- The grea...Why focusing on CO2 and AGW is silly. <br /><br />- The greatest contributors of warming/cooling are ocean surface flux, heat flux, humidity and clouds. Also consider light input and planet wide albedo as well as magnetosphere strength. CO2 has a very low overall impact. Insulators (CO2) have a non-linear diminishing return. The more CO2 that is put up, the less insulating effect it will have per unit.<br /><br />- Modern CO2 level is as a generous 400ppm. <br /><br />- Precambrian CO2 was 4500 ppm, Oxygen @ 12.5%, temp +7C modern.<br />- Ordovician CO2 was 4200 ppm, Oxygen @ 12.5%, temp +2C modern level. <br />- Carboniferous CO2 was 800ppm (over double today), yet it has a nice Oxygen level at 32.5%. Also, temperatures were the same or slightly lower than today's temp. <br />- Jurassic CO2 1950ppm, 26% O2 and ~ 3C above modern. (Thats about 5x todays CO2, more oxygen, similar temps).<br />- Cretaceous CO2, 1700ppm, O2 @ 30%, temps about 4C higher. This is the realm of the greatest biodiversity the world has ever seen. Lots of oxygen, lots of CO2 but no man-made AGW. Imagine living in an atmosphere with this much O2! Lots of CO2 around to feed plants.<br />- Neogene to modern. Where we are today. Most of the atmospheric oxygen loss (about 8% of the total) occurs before industrialization. <br />- At no point, even with many times the current CO2, did the greenhouse effect run away. <br /><br />Seems to me that people should consider planting trees that produce a lot of O2 for every CO2 processed. That would help albedo and do more for the world than any attempt to prevent CO2 changes. Build nuclear power plants (lots of them) and try to get to fusion. Then pollution (everything BUT CO2, which is plant food) can finally slow down. Things like MTBE, metals, etc. CO2 is the last thing to worry about - really.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-61569498554343748022010-01-12T18:18:39.361-05:002010-01-12T18:18:39.361-05:00Thomas:
You raise a good point -- the temperature ...Thomas:<br />You raise a good point -- the temperature that is given, at all points, is the ice core's isotopic temperature. The recent isotopic temperature was taken as the zero point. (The most recent plotted point is for -0.57 C because that's a lagged temperature -- for 1000 years ago, not for 'today'.)<br /><br />Going between 'global mean temperature' and 'ice core isotopic temperature' is not a trivial task, and one I've argued with ice core people about.<br /><br />It doesn't, however, affect the conclusions here. There was a relationship between temperature (ice core isotopic temperature) and CO2 (ice core air bubble CO2) that held for 799,000 years. And the most recent observations are drastically far away from that relationship.Robert Grumbinehttps://www.blogger.com/profile/10783453972811796911noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-74788684881803629522010-01-12T16:38:57.254-05:002010-01-12T16:38:57.254-05:00The temperature data you use are from EPICA, but a...The temperature data you use are from EPICA, but are those really representative of global temperature so that you can put the current temperature anomaly in the same diagram the way you do?Thomas Palmnoreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-82204958694724252962010-01-11T00:03:13.108-05:002010-01-11T00:03:13.108-05:00carrot eater said you didn't even give the mos...carrot eater said <i>you didn't even give the most simple line of evidence, based on the conservation of mass.</i><br /><br />Quite right, carrot eater.<br /><br />The fact that the ocean surface waters and green land plants are net sinks of CO2 effectively <i>sinks</i> the idea that the atmospheric increase over the past century is "natural" (eg, due to ocean out-gassing due to increased temp)<br /><br />I commented on that in a post (<a href="http://halgeranon.blogspot.com/2009/04/of-upward-slopes-and-isotopes-2.html" rel="nofollow">Of Upward Slopes and Isotopes (2)</a>) a while back (under "Key point")<br /><br />But I think the <i>illogical</i> nature of the claim that " temperature increase over the past century was responsible for the CO2 increase" is a bit more intuitive/obvious from the above graph than it is from the carbon flux argument not least of all because one can see it with one's own eyes. <br /><br />The fact that "You can't get here from there" -- ie, to current CO2 level of about 385ppm from level of 280ppm about a century ago with the small temperature change that has actually occurred -- is literally staring one in the face when one looks at that graph.Horatio Algeranonhttps://www.blogger.com/profile/12988805467080448954noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-23250758743910335772010-01-10T19:02:11.760-05:002010-01-10T19:02:11.760-05:00Stephen:
We differ because in one place, I make an...Stephen:<br />We differ because in one place, I make an arithmetic error, and in the other, you and I are computing different things. My simple arithmetic error was that I subtracted 1 from the wrong number. We have to subtract 1 from our count of data points when we work with the lagged data. We start with 1 data point per 1000 years, for 800,000 years. My error was thinking this was 800 points. We actually start with 801 -- a data point for time 0 ('today').<br /><br />The standard deviation issue is not quite as obvious, but still simple. When you computed the standard deviation, you did it for standard deviation of all CO2 observations. This is a correct computation for assuming that we know <i>nothing</i> about the CO2 concentrations. In mine, after verifying that the correlation between temperature and CO2 was exceedingly high, I decided that we did know <i>something</i> about CO2 variation -- that it correlates to temperature variation. The standard deviation I compute is for the difference between the best fit line (that knows high temperatures correlate to high CO2) and the observed CO2. Since CO2 correlates strongly with temperature, the standard deviation I get for this 'residual' (difference between expected and observed CO2) is very much lower than you get.<br /><br />It's something like what happens in murder mysteries. Detective finds mud at the crime scene. It's muddy outside, so no surprise (your original large standard deviation). But the detective then looks at the mud outside, which is black, and the mud by the body, which is reddish, and there's a lot of surprise (my much smaller standard deviation -- much greater suprise to see the 365 ppm CO2). We have <b>a clue</b>. I'll take this up in its own post later this week. This sort of issue is very important to doing science.Robert Grumbinehttps://www.blogger.com/profile/10783453972811796911noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-43356513447968736182010-01-10T15:31:48.540-05:002010-01-10T15:31:48.540-05:00I'm a little late coming to this party, so ple...I'm a little late coming to this party, so please pardon me. <br /><br />As the article suggested, I downloaded the dataset from the link given in the BBC article (800000.xls).<br /><br />Using Excel CORREL() function,<br />I was able to calculate the correlation coefficient (R) value of .88 for correlating the CO2 concentration with the "same-year" temperature figure, and an R = .89 for correlating CO2 concentration with the "1000-yr-ago" temperature. So far those match the article.<br /><br />However, the article says the standard deviation is ~11ppm. Using the Excel STDEVP() function, I'm getting 26.03 over the range D14:D813 (the CO2 concentration data column). I get the same using STDEV(), but differing in some smaller-order places. (I also make it to be 800 data points/pairs where the article says 799 points/pairs; but I don't see how that would make a difference in the standard dev. value I'm getting.)<br /><br />My question is why is my standard deviation calculation different from that presented in the article?<br /><br />Thanks,<br />Stephenstephennoreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-51504959772656110282010-01-10T15:27:36.408-05:002010-01-10T15:27:36.408-05:00Horatio, regarding people who think the current at...Horatio, regarding people who think the current atmospheric accumulation of CO2 is mainly caused by an increase in temperature (itself caused by.. who knows what): And you didn't even give the most simple line of evidence, based on the conservation of mass.<br /><br />We know how much carbon is being added to the system through combustion and cement. We also have some idea of deforestation. The accumulation in the atmospheric amount is well measured and is about half the input amount, with a good portion of the rest accumulating in the ocean (and lowering the pH). Given all that, how would these people redraw the carbon cycle by adding a input source that's larger than combustion/cement, and still both obey the conservation of mass and be anywhere near consistent with observations? <br /><br />When there are so many consistent lines of evidence against an idea, you'd think people would drop it.carrot eaternoreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-56617126209612580272010-01-10T11:47:42.014-05:002010-01-10T11:47:42.014-05:00As Penguin points out, given the strong correlatio...As Penguin points out, given the strong correlation and the fact that the current CO2 level is so far above the least squares line on the graph (5-10 std deviations is my "eyeball" guess), it is pretty clear that we are in a completely different regime.<br /><br />In fact, assuming the relationship on the graph and assuming that temp change causes CO2 change would lead one to <i>expect</i> only about a 6ppm increase in CO2 level for the 0.75 C rise in mean global temp that we have seen over the past century.<br /><br />Of course, in actuality, we have seen about 16 times that CO2 rise (100ppm).<br /><br />But despite this disagreement between expectation (based on the graph) and observation (and despite the isotope evidence which shows that most of the rise was most likely due to fossil fuel burning!!), there are still some (including at least one prominent climate scientist) who propose that the increased mean global temperature in recent history might (somehow) account for most of the increase in atmospheric CO2.<br /><br />That's just illogical.Horatio Algeranonhttps://www.blogger.com/profile/12988805467080448954noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-47391491698473437102010-01-10T08:32:38.370-05:002010-01-10T08:32:38.370-05:00Actually I'm a little spoiled by what I normal...Actually I'm a little spoiled by what I normally do, where the R^2 values are rather higher. But there the data are different, the analysis is different, the objectives are different. That's just a reminder to not let instincts carry over from topic to topic, if there are such differences.carrot eaternoreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-12984615592515285362010-01-09T20:48:00.215-05:002010-01-09T20:48:00.215-05:00carrot:
glad to see you take up some of the proje...carrot: <br />glad to see you take up some of the projects I mentioned. Compare the R^2 you had for interglacials to what I found for the pre-1959 temperature-CO2 observations. It'll look familiar.<br /><br />Also have a look at the correlations for temperatures less than -1. You might be surprised here, too. Especially for what happens in the coldest, say, 100 observations (the most thoroughly glacial temperatures).<br /><br />By the way -- for 800 data points, explaining 28% of the variation is usually doing quite well. You're a little spoiled with seeing the 79% that we have for the full range of data.Robert Grumbinehttps://www.blogger.com/profile/10783453972811796911noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-1714972937897765302010-01-08T13:47:53.402-05:002010-01-08T13:47:53.402-05:00Ah, apologies to all. I now see how I misread the...Ah, apologies to all. I now see how I misread the description of the temperature data.<br /><br />Before moving on to orbital forcing, a couple loose ends from our suggested homework:<br /><br />Using the natural log of CO2: the R^2 actually gets a bit worse from 0.79 to 0.77. Not surprising, given that other forcings are doing the driving here.<br /><br />I also wanted to see if this plot could be used to detect two different regimes, one for the interglacial and one for the rest of the time. We may not know exactly where the carbon comes from at the end of the ice age, but my gut tells me that it's a mechanism that is somehow less accessible under current conditions. Why? Because if it were active in the same way, we should be able to physically observe it in real time today.<br /><br />So, I arbitrarily set "interglacial" to be anything above -1 C. During the interglacial, the R^2 is horrible, 0.28. The trendline slope is also weaker. I think that is consistent with my guess?carrot eaternoreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-68579207237574446952010-01-08T13:37:10.976-05:002010-01-08T13:37:10.976-05:00Lou:
It can be more than a little unsettling to f...Lou:<br />It can be more than a little unsettling to find out more. I have to lean on 'Forewarned is forearmed' (even when some folks seem to want no warning). Or I remind my wife of the fuller quote from Pope about 'a little learning is a dangerous thing' --<br><br /><i>A little Learning is a dang'rous Thing;<br />Drink deep, or taste not the Pierian Spring:<br />There shallow Draughts intoxicate the Brain,<br />And drinking largely sobers us again.</i>Robert Grumbinehttps://www.blogger.com/profile/10783453972811796911noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-46645237298349274192010-01-08T13:11:18.434-05:002010-01-08T13:11:18.434-05:00jg, carrot eater:
You have, of course, named the s...jg, carrot eater:<br />You have, of course, named the source I was asking people to think about. The orbit affects both temperature and CO2 (independently). Thanks, jg, for the link to another source for orbital parameters. I have a different one, not as usable by everybody.<br /><br />It is indeed still 65 N that is taken as the latitude to work with for ice ages. <br /><br />Regarding the present CO2 or temperature:<br />The data set (link provided in the article) is not giving averaged values. The 'reference' was the one time an average is used. Deviations from the reference, though are for short term temperature (low decades) on the ice sheet, not 1000 year averages. Regarding Gary's possible question, it is indeed correct that the temperature which is being plotted against the CO2 is the temperature for 1000 years ago (from the ice core) -- because that's the best approximation to the lag.<br /><br />One thing looking at the data says, now that we've looked at all of it, is that you <i>cannot</i> consider the current CO2 to be part of the usual relationship that used to exist. Human sources have swamped the previous connection, placing us in an entirely new regime.<br /><br />But you have to look at the data before you decide this, so I kept it on the plot. <br /><br />Next up will be to look at the connections between orbital variations (Milankovitch variations) and the temperature and CO2. Even with only 3 'things', there are 125 possible models that could be considered.Robert Grumbinehttps://www.blogger.com/profile/10783453972811796911noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-43607037923068585462010-01-08T12:59:56.384-05:002010-01-08T12:59:56.384-05:00CarrotEater, I got this link from OpenMind a few m...CarrotEater, I got this link from OpenMind a few months ago:<br /><br />http://www.imcce.fr/Equipes/ASD/insola/earth/earth.html <br /><br />The program on this page will calculate orbital parameters and insolation values going back millions of years.<br />I've pulled out the eccentricity, climatic precession, and tilt values over the past million years and have been working them into an animated illustration. I'm in the process of adding the insolation values and welcome any recommendation as to which latitudes insolation is most important (e.g., is it still the 60-65 degree north zone that is thought to tip the balance between ice age and interglacial?)<br /><br />jgjghttps://www.blogger.com/profile/00588440067862480858noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-49455042974389072142010-01-08T11:18:14.801-05:002010-01-08T11:18:14.801-05:00If you plot the data against time, it becomes quit...If you plot the data against time, it becomes quite striking how warm the previous interglacial was. I take it that the orbital forcing was much stronger back then. In some crude sense, you can say that we're trying to use extra CO2 to catch up to where the Earth was back then.<br /><br />There is maybe another interesting way to show the relationships here. If you plot the CO2 level against the orbital forcing, I think you should see about same level of correlation. But the modern point will again be a lonely outlier. This would underscore that CO2 used to be a feedback to the Earth's orbit, but is now a forcing of its own.<br /><br />So, er, does anybody have a data source for the orbital forcing over these time scales?carrot eaternoreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-32108574507293696002010-01-08T09:39:13.348-05:002010-01-08T09:39:13.348-05:00I might be reading something wrongly, but I suppos...I might be reading something wrongly, but I suppose there might then be a slight issue with the phrasing here.<br /><br />If the CO2 level at 2000 AD is being paired with the average temperature between 0 and 1000 AD, then the lag being used is somewhat more than 1000 years. It's tempting to call that an average lag of 1500 years, but I don't know if that's a good way to phrase it. <br /><br />None of which really matters. Just nitpicking.carrot eaternoreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-9980118573717585002010-01-08T04:11:20.144-05:002010-01-08T04:11:20.144-05:00Gary Thompson,
There are two additional reasons t...Gary Thompson,<br /><br />There are two additional reasons that the current datapoint is at a lower temperature than what you would expect from the glacial period relationship:<br />1) Other climate forcings at work<br />2) Time lags in the climate response<br /><br />ad 1) During the ice ages, there wer other forcings and feedbacks besides CO2: notably orbital forcing and albedo feedback. CO2 is responsible for about a third to half of the forcing (from memory; someone correct me if I'm wrong with this number). Currently there are also other forcings at work, notably other GHG and aerosols (who nearly cancel each other though). This means that the expected temp at current CO2 levels is about half to a third of what you would expect based on the historical relationship (this ties in to Hansen’s system sensitivity of 6 deg for the ice age cycles, whereas the Charney sensitivity is thought to be closer to 3 deg per doubling of CO2. Bob’s plot actually has a delta T of around 18 deg for a CO2 doubling, which would be consistent with CO2 being a third of the forcing and a long term earth system sensitivity of 6; merely thinking out loud here. Distinguishing between forcings and feedbacks in the definition of sensitivity gets confusing)<br /><br />ad 2) The current climate is not in equilibrium with the current forcing, which means we expect the temperature to be lower than the forcing would eventually cause. In the absence of significant ice sheets response to the warming, we’d expect an eventual warming of around 2 degrees above pre-industrial with just the current CO2 forcing ignoring the fact that there are other forcing s at work, but as I mentioned above, they close to cancel each other). This is about twice as low as you’d expect from the ice ages relationship, because the ice sheet response was a significant positive feedback at those times, and we think/hope that they won’t be in the current epoch.<br /><br />BartAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-32605383588838850642010-01-08T00:21:32.936-05:002010-01-08T00:21:32.936-05:00gary thompson:
Look carefully at what is plotted....gary thompson:<br /><br />Look carefully at what is plotted. First, our host tells us that he plotted temperature with a 1000 year lag. Then, if you go to his data source, you'll also see that each temperature point is averaged over a 1000 year span.<br /><br />So the temperature associated with 365 ppm in the plot is the average temperature (someplace in Antarctica, I presume?) between 0 AD and 1000 AD. <br /><br />So the 365 ppm represents the year 2000 AD, but the corresponding temperature does not.carrot eaternoreply@blogger.com