tag:blogger.com,1999:blog-8666091.post4627939543253331912..comments2020-03-13T03:28:45.250+01:00Comments on The Reference Frame: Why the feedback amplification can't be both positive and highLuboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.comBlogger9125tag:blogger.com,1999:blog-8666091.post-11352668529682470192010-03-01T15:21:02.016+01:002010-03-01T15:21:02.016+01:00Dear Nick,
life has surely survived ice ages and ...Dear Nick,<br /><br />life has surely survived ice ages and interglacials but the conclusion in the paper - which is just a nice try - seem to be exactly upside down.<br /><br />The very graphs he uses show that the global mean temperature wants to be in the central region most of the time, while it always and quickly "reflects" from the extreme high and extreme low temperatures (which seem to be nearly unbreakable bounds).<br /><br />So it means that these "extreme" temperatures during the glaciation cycles are not stable at all. Quite on the contrary, they're the most unstable points in the graphs. And they're unstable exactly because of negative feedbacks that regulate the deviations from the long-term average whenever the deviations are high enough.<br /><br />So I think that the equivalences stated in the article and in your comment are just completely wrong. By the way, the intermediate temperatures don't persist at constant levels. But that doesn't mean that they're "unstable" in any sense, surely not "runaway unstable" or "more unstable than the extreme temperatures". Temperatures are changing all the time, because of internal variability (weather that accumulates) as well as external influences. But the very fact of a "change" doesn't imply an "instability". This is just a completely bogus, mathematically sloppy way of using all these terms.<br /><br />Best wishes<br />LubosLuboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-33487964120509263432010-03-01T07:30:13.480+01:002010-03-01T07:30:13.480+01:00Here's a guy (I.J. Katz) who argues that runaw...Here's a guy (I.J. Katz) who argues that runaway feedback (in both directions) is entirely normal for Earth (all that water makes for a bistable system).<br />[http://lanl.arxiv.org/abs/1002.1672]. Life seems to have managed to survive both the ice ages and the <br />tropical heats.nick herberthttps://www.blogger.com/profile/12806604589435880363noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-4079786300550490362010-02-27T15:50:20.897+01:002010-02-27T15:50:20.897+01:00Dear Leonard, thanks for your interesting point.
...Dear Leonard, thanks for your interesting point.<br /><br />It is however a double-edged sword. If it prevented the Earth from too big fluctuations in the past, it may do the same in the current era, too.<br /><br />Moreover, it takes a lot of change for the nonlinearity of T^4 to kick on. Set the current temperature, 15 °C or T = 288 K, to one, and write T as (1+t). Then (1+t)^4 = 1 + 4t + 6t^2 +...<br /><br />Keeping only the 4t term is linearization. The next term is 6t^2. It is only equal to the linear term for t=2/3 which is 192 Kelvin of temperature. This is a huge temperature change. For temperature changes much smaller than 192 K, the linear approximation of T^4 is almost perfect.<br /><br />There are other nonlinear things, too. But many of them are similarly accurately linear for the whole interval of temperatures that dominated the whole history of Earth. I don't want to claim that most processes in the climate are linear. But what I want to claim is that if the global temperature variations from the mean admit a very nice linearized theory.<br /><br />Cheers<br />LMLuboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-89868364959308179102010-02-27T14:51:12.230+01:002010-02-27T14:51:12.230+01:00Lubos,
I am a CAGW skeptic (and becoming doubtful ...Lubos,<br />I am a CAGW skeptic (and becoming doubtful of even significant AGW) and believe the clouds and long term ocean currents dominate the climate variation. However, I want to point out that the feedback analysis you made leaves out the T^4 feature of the gray or black body, which would limit runaway temperature. The linear feedback series is only a small variation approximation.Leonard Weinsteinhttps://www.blogger.com/profile/02125857972902059097noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-79320306976236135242010-02-27T02:38:42.046+01:002010-02-27T02:38:42.046+01:00Dear Lubos, the "measurement" of the con...Dear Lubos, the "measurement" of the consequences of the calculation is hypothetical, and I agree that that the "calculation" of it is theoretical, and valid "calculations" of it are by no means unique. <br /><br />I prefer to refer to "damping" rather than "feedbacks" that must be the origin of overall stability.Brian G Valentinehttps://www.blogger.com/profile/01523059818774910427noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-85338968925949098472010-02-26T19:36:50.037+01:002010-02-26T19:36:50.037+01:00Dear ScientistForTruth,
do they have to be indepe...Dear ScientistForTruth,<br /><br />do they have to be independent for the central limit theorem to hold? Yes and no. Not really.<br /><br />The sum of a large number of independent, equally distributed variables is the simplest context to prove the central limit theorem.<br /><br />But the theorem holds much more generally. What the "large number of independent quantities" really requires is that the "total amount of independence" in all these quantities has to be large. So there's absolutely no problem if you sum 100 different effects that are mutually correlated - but not perfectly correlated - with each other.<br /><br />I totally share your negative-feedback intuition although my explanation would be less divine. Well, if there are positive feedbacks, there are much larger chances that they will become runaway positive feedbacks, and these systems will jump to a runaway behavior and drift elsewhere, until the exponential runaway approximation breaks down. <br /><br />Then they settle into a different regime that is dominated by more negative feedbacks. So in some sense, my argument is Darwinian in character - systems with positive feedbacks are not the fittest who survive - but please don't view this alternative explanation as an attack on God. ;-)<br /><br />Cheers<br />LubosLuboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-15346831620984700272010-02-26T17:47:26.338+01:002010-02-26T17:47:26.338+01:00Don't the feedback factors have to be independ...Don't the feedback factors have to be independent random variables to end up with a normal distribution and central limit theorem? Can we really say they are independent?<br /><br />I know it's not a scientific argument, but from a theological perspective any grand Designer wouldn't make a world with runaway feedbacks. We wouldn't do that ourselves, would we, if we we were having a stab at designing it? Another way of looking at it (metaphysically, but something that atheists might like to buy into) is that of all the potential universes that could exist, only the ones with negative feedbacks could endure, and as this one certainly endures, it must generally have negative feedbacks.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-87260695697719993312010-02-26T08:59:41.115+01:002010-02-26T08:59:41.115+01:00Dear Brian,
it's not "hypothetical"...Dear Brian, <br /><br />it's not "hypothetical", it's "theoretical", because it's not a result of a random guess but a result of a calculation based on empirically established laws of physics. <br /><br />The calculation doesn't have to directly correspond to reality - and indeed, it quantatively doesn't agree because the feedbacks are likely to exist, with one sign or another. But it's still an important calculation. The idealization in it is "not infinite" and my personal guess is that the total feedbacks won't be too high in either direction.<br /><br />Cheers<br />LMLuboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-36804931143844001212010-02-25T23:53:04.616+01:002010-02-25T23:53:04.616+01:00That "1.2 deg C" from "CO2 in the a...That "1.2 deg C" from "CO2 in the air without feedback" is entirely in the realm of the hypothetical, because there is no way to measure it. <br /><br />That supposed figure is within natural variability of the atmosphere, and there is no way to decompose all the effects to ascribe a temperature change of that magnitude to a unique influence. <br /><br />This "greenhouse gas theory" is by far the most contemptible misuse of the word "science" in the history of human thought. It is so vile that it makes me angrier than I have ever been.Brian G Valentinehttps://www.blogger.com/profile/01523059818774910427noreply@blogger.com