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    scienceofdoom You said "Models don’t assume that" Yet in Water vapor feedback and global warming 2000 Isaac M. Held and Brian J. Soden Held says "There is no ambiguity as to how to compute the relative importance of different regions for water vapor feedback in a model that predicts changes in water vapor concentrations; the confusion only arises from differing presumptions as to a plausible model-independent starting point. Our justification for Equation 21 is only that it better resembles GCM predictions." -It seems GCM models assume [presume] water vapor feedbacks that are not realistic and knowingly use them because they inflate the amount of heat and hence temperature produced. Contrary to what you said. You know this yet chose to ignore or dismiss it. Why? Sorry about the sophistry barb but then...

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    Nick Stokes | December 12, 2018 at 12:34 am | Reply "And the 76% has wide error bars." After Resplany this is small fry Nick.

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    angech, a prediction is different from a presumption.

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    Nic, to compare with AR5 Figure SPM.10 you need to divide by that 0.64 you assumed because their temperature change is the whole temperature change including all other proportionate forcing factors, not just the CO2 part. 1.05/0.64=1.64, which is more in line with other observationally based estimates.

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    Jim, my profession involves lab science. I do extensive research of other's reported findings and then validate them if I can. Then I form new hypotheses and devise new experiments to test them. Even with great analytical equipment it's still very hard to make a new important and unique discovery. I say this because I know however hard my challenges have been climate science is even more complex and has less tools. Climate science has made zero progress to constrain climate sensitivity in their ~40-year effort. Knowing this you express matter-of-factly that you know the answer. You say its simple physics, just provide a given CO2 concentration and you can supply a global temperature. I am trying to point out facts that you <i>know</i> that should contradict such claims. And it's very difficult to know whether your misconstruing the science and my points about the science is intentional, so I will assume not and try to fix them. Here goes: "I define when warming started as when temperatures started to exceed anything in the previous 100 years and that did not happen until the 1900’s." Jim, proxies are not thermometers, and thus even if they worked perfectly they would never provide the resolution necessary for you to conclude current warming or cooling rates are unprecedented. They may well be but we don't know and can't know with current data. This is half of the "Mike's Nature trick" by the way, pasting high res thermometer records over the smoothed proxy reconstruction to make the rise look sharp and unprecedented. The other half of the trick was deleting the proxies to "hide the [their] decline" in the late 20th century and thus invalidating the proxy's entirely. "As for PAGES2k, if you have a preferred source that you think is better and shows warming startting well before 1850, you need to show where your statement came from." I had linked my statement to its source. I don't know how good it is. I grant that there are contradictory views about when the LIA minimum was, but I think most use the Maunder Minimum like my source did. By definition the recovery starts after the minimum. If you are placing the minimum at 1850 then, as I said, you should be showing a great amount of gratitude to Standard Oil for saving us from the natural end of our pleasant but limited interglacial. "Climateaudit have not disputed when the warming started as far as I know." A high portion of your statements simply assume unprecedented warming at a set time, before which there was a static paradise. This is also common for those whose only knowledge of climate science comes from Mashable, Vox or Pop Sugar. "PAGES2k is not about solar, but it is about temperatures." Yes, my point was that your rely on them for your plot of past global temps, that you rely on to determine the "start of warming" while attributing the LIA to solar. I simply pointed out that PAGES2K do not say the LIA was solar caused.

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    This is Nic's claim that observed is less than CMIP5. If CMIP5 is 1.6 and obs is 1.33 with a big error range, it doesn't cast much doubt on CMIP5.

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    I start from the physics. It predicts that changing the forcing leads to a change in warming. This could be a strong signal when the forcing change is faster than anything natural, and it turns out it is. Now we can measure the response, and it is sharply 2.3-2.5 C per effective doubling. They didn't believe Galileo at first. As for when warming started, you can look at the 1800's and easily see no trend. You look at the 1900's and there is no doubt about a trend. That's why I say warming really started in the 1900's. Maybe you want to thank fossil fuels for preventing more icy winters. I say fine. If you believe that, you should also believe the significance of doubling CO2. I'll take it. There's a group called 350.org who say 350 ppm is ideal. Going by paleoclimate, it prevents Ice Ages but also doesn't melt ice caps like 450 would. Maybe you can subscribe to that view now. Re:climateaudit, you are putting more weight on those tree rings than they say you should. They just throw dirt, but don't do the extra work of removing proxies they don't believe. Why not, you need to ask. An incomplete study at best.

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    "You have not supported your previous statement where you appeared to discount that the Holocene Optimum was the Holocene warm point until recently." If I appeared to do that it was by accident. The Holocene Optimum <i>was</i> the Holocene's warmest point until debatably the present. My point was that it occurred 3000 years post Milankovitch's optimum, thus Milankovitch may not necessarily be responsible for everything when CO2 is unchanging. "The global mean temperature is constrained by the energy balance on long time scales." Yes. I can agree with that. However, the energy balance can be affected by scores of influences over long time scales. There are likely some positive and negative feedbacks not yet understood. The vast energy reservoir of the seas has the power, if perturbed, may have sudden severe abilities beyond ENSO, for example. Javier's great series of posts touched on some of these possible influences. "Each hemisphere may vary (e.g. ocean circulation changes), but the global sum is constrained by the energy balance." Again, you seem to miss the fact that each hemisphere has independent means to radiate energy from the surface, for example, with increased cloudiness or ice albedo, and also to bring up or sink energy into the seas. A well known example of such a NH event is the Younger Dryas Period during our interglacial transition. "The sun, other GHGs, volcanoes, aerosols are all in there, but CO2 dominates the change with +2 W/m2 and counting at 400 ppm. It reaches +5 W/m2 at 700 ppm." Jim, in your climate sensitivity math, you <i>did</i> remember that warming cancels forcing? Right?

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    The strongest Milankovitch forcing was what ended the Ice Age. Prior to the Holocene Optimum, the albedo was still high and declining, so it was cooler even with the strong Milankovitch forcing. Melting the ice caps took some thousands of years because the precession effect is relatively weak. If the forcing changes by 1 W/m2 you first get an imbalance and then warming. 1 W/m2 is a fraction of a percent, but has a measurable effect on temperatures and ocean heat content especially whan applied over decades. CO2 has already added 2 W/m2 on its way to several more. The effects of this are as expected. Doubling CO2 is the forcing equivalent to adding 1% to the solar strength. Few would question that would lead to warming. Changing the forcing, e.g. by moving the sun closer, changes the equilibrium temperature. The imbalance is still positive so we are still lagging the equilibrium temperature. Just mainstream science here.

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    "They didn’t believe Galileo at first." Jim, are you saying the mult-billion-dollar governmental-academic climate machine is not an establishment? The story of Galileo is a warning against consensus and establishment set beliefs. At least it was when I was taught. I'm sure its a different lesson now. "As for when warming started, you can look at the 1800’s and easily see no trend. You look at the 1900’s and there is no doubt about a trend. That’s why I say warming really started in the 1900’s." Jim, nobody noticed the trend until the late 1970s. In the early 1970's there were many concerned the 20th century was headed toward a crash landing back to the ice age. Paul Ehrlich's best seller, The Population Bomb, records that beautifully, where he was not sure if man-caused pollution would freeze us or fry us, but he was certain it would be catastrophic. Jim, I actually think 350-400ppm is likely ideal. But if sea level rise from melting polar glaciers becomes apparent we will have the technology to combat it. Talking about this technology is currently tabu because the elite do not want to give the masses any relaxation of vigilance for alternative energy. (See <a href="https://keith.seas.harvard.edu/publications/toward-responsible-solar-geoengineering-research-program" rel="nofollow">David Keith's Harvard paper</a>.) In this thought I can empathize except I give the masses a little more credit. I think they would buy the argument that we need nuclear, wind and solar to bridge us to fusion before fossil fuel become scarce and more expensive.

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    One thing that's been a huge problem with these climate models is their tight fit with the historical record. If you have a model that isn't taking into account some level of climate variability (several of these models have acknowledged error of that sort), then you should see the error in the past as well as in the future - that climate variability didn't start tomorrow! A common perverse result is that tightening the fit to existing data (by adjusting the loose parameters of the model) can then worsen the extrapolations to the future.

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    Feedbacks are calculated on the basis of fundamental physics. http://www.climatechange2013.org/images/figures/WGI_AR5_Fig7-9.jpg And net feedback is negative even allowing for the vagaries of cloud and opportunistic ensembles. http://www.climatechange2013.org/images/figures/WGI_AR5_Fig7-10.jpg

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    Global-scale multidecadal variability missing in state-of-the-art climate models - https://www.nature.com/articles/s41612-018-0044-6 Missing in both EBM and GCM it appears.

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    It would be nice if you would answer the question. Do the math. Oh, I forgot. Math is hard.

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    It's more that I tend not to answer questions while I'm asleep. Nor ones that make no sense to me. I've no idea what the 'MM emissions' you refer to are. But ocean physical chemistry and gas exchange characteristics are well established and the principles are not worth arguing about, although things like ocean circulation and depth penetration of CO2 and heat have an appreciable influence on the outcome. "How do you know what is going to happen to that CO2? How do you know that much of it doesn’t get turned into rock chemically?" I believe it is well established that all or most of the emitted CO2 will eventually be permanently absorbed by silicate rock weathering. The problem is that this is an extremely slow process, taking tens to hundreds of throusands of years. On a shorter but still long timescale, ocean sediments will absorb some CO2 as CaCO3. May I suggest you read Box 6.1 in Ch.5 of IPCC AR5 WG1? The percentages may be somewhat too high and/or timescales over-long, but the general picture it presents seems sound to me. Even though one may not agree with all of it, there is a lot of useful scientific information in the AR5 WG1 report.

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    Hi Nick, thanks for your comment. "But I think you are low-balling the estimate." Not at all. In fact, I have not adjusted up my estimate of total forcing to reflect the AR5 estimate of the very high (2x to 4x) efficacy of Black carbon on snow forcing. "The AR5 itself gives CO2 forcing as 1.68 W/m2 out of 2.21, or 76%." AR5 only gave values to 2011, but they can be extended on a similar basis. My 1.67 W/m2 CO2 forcing is almost identical to the AR5 basis, as I extend it to 2016, which gives 1.66 W/m2, close to your 1.68 W/m2. However my 2.6 W/m2 total forcing - which reflects the forcing basis used in Lewis & Curry (2018) is 0.26 W/m2 higher than the 2.34 W/m2 I estimate on the AR5 bases for 2007-16. The difference in total forcing is explained as follows: Other GHG (Methane & N2O) +0.11 : new (Etminan et al 2016) GHG forcing-concentration bases Aerosol & Ozone +0.14 : new (Myhre et al 2017) post-1990, using updated emissions Miscellaneous +0.01 : roundings etc. I don't know how you arrived at your 2.21 W/m2 total forcing change - perhaps that is anthropogenic only, which is almost 0.1 W/m2 lower than for total forcing. "And the upward revisions of land use emissions seems speculative; without it, emissions are 530 Gtons." The IPCC AR5 based estimated 1850-82 mean to 2007-16 mean land use change (LUC) emissions part of the 530 GtC is (180 - 28 + 1) = 153 GtC. The Global Carbon Budget 2018 estimate is 181 GtC, 28 GtC higher. Their LUC estimates have been increasing significantly over the last few years; the Global Carbon Budget 2015 estimate of total 1850-2010 LUC emissions (the range of years it gave them for) was 153 GtC; in the 2018 budget it was 38 GtC higher at 191 GtC. Moreover, there is another recent paper, Sanderman et al (2017) PNAS, which estimates that anthropogenic soil carbon emissions, which were not focussed on in the Arneth paper, have been underestimated by approaching 100 GtC, although much of this relates to before 1850. So I think my addition of the Arneth et al (2017) estimated upwards adjustment of 35 GtC LUC emissions to adjust the AR5 estimate is most probably conservative. "And the 76% has wide error bars" This post focusses on the difference in central estimates, not their uncertainty ranges. But I agree that there is significant undertainty in my TCRE value, which represents a median estimate.

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    Nick, I think your question is answerd after reading the linked footnote XI?

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    "My point was that it occurred 3000 years post Milankovitch’s optimum, thus Milankovitch may not necessarily be responsible for everything when CO2 is unchanging." I reconcile that with the lag required for northern lands to fully melt the ice sheets and for ocean SST's to recover.

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    Thank you, Nic Lewis, for another excellent analysis and CE post.

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    Jim D, over the historical period to date CO2 forcing is a much higher proportion of total forcing in climate models than per observational estimates, largely because aerosol forcing is more strongly negative in models. It is more relevant to compare CO2 with total forcing over the entire period until approximately 1000 GtC emissions have been reached; TCRE is usually estimated for 1000 GtC emissions. Over that period, only 14% of the total model forcing change was accounted for by non-CO2 forcing, based on the forcing dataset for the middling RCP scenarios. My 2.0 C estimate of the TCRE implicit in AR5 Fig. SPM.10 allows for that. See my note [iv].

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