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    Hans, 600 ppm is a scenario with about 3 C warming, while at the same time requiring more efficient energy use (or fossil fuel replacement) as the world's population grows and develops. It would represent a failure to mitigate effectively while it does represent a weak attempt at it.

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    JimD writes "I’ve seen it all before, and it is less than convincing" Strange, because this is the first time it has been seen by other than the author. Where, exactly, did you read it all before? Geoff

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    For example, when you talk about UHI, it is not very promising. What do you have to say about that that the previous lot missed?

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    Yes, you are using a second definition of feedback, when most people use the other one that is more useful because it contains the concept of a positive feedback too. And I am not sure you know what the other one is. In the other one, the concept of a no-feedback response makes sense, while in yours it is a self-contradiction. Just say what's wrong with this article. This definition is nothing new, but apparently it is to you. https://judithcurry.com/2010/12/11/co2-no-feedback-sensitivity/

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    Welcome to the 6th hottest year on record, JD. The hot blob off Alaska is kaput. Not much to look forward to, eh? You think the El Nino will be a bad one?

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    Do you think this decade will be warmer than the last one and all the previous ones? For climate it is the decades that count. This is the 30-year temperature record. Straight up, not even a pause since 1980. CO2 doing something similar, not the sun (also displayed). http://woodfortrees.org/plot/best/mean:120/mean:240/plot/esrl-co2/scale:0.01/offset:-3.25/plot/sidc-ssn/scale:0.005/mean:80/offset:-0.6/mean:40/from:1850/plot/best/from:1988/trend

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    Which people would these be? Not the IPCC, not Isaac Held, not the graduate course notes #jiminy keeps misapplying. The IPCC and Held feedbacks have been shown several times - and the closest $jiminy comes to acknowledging this is calling it sloppy thinking. Positive and negative feedbaxks are shown. Positive feedbcks make the net less negative and the ECS higher. "The Planck feedback is the most basic and universal climate feedback, and is present in every climate model. It is simply an expression of the fact that a warm planet radiates more to space than a cold planet." Does Judith Curry understand this? "Determination of the no feedback sensitivity has two parts: - calculation of the direct radiative forcing associated with doubling CO2 - determination of the equilibrium change of global mean surface temperature in response to the CO2 forcing" Easy enough to calculate: ECS = -F/λ = -3.7 W m^-2 / -3.2 W m^-2 K^-1 = 1.2 K where -3.2 W m^-2 K^-1 is the temperature (Planck) feedback. Positive feedbacks make net λ less negative and ECS is higher. So nothing wrong with the definition - but the terminology has confused #jiminy. It is more precise to call it the Planck response than the no-feedback response - as he does interchangeably. It is the same thing. There are not two definitions except in #jiminy's confused refusal to accept that increased emissions in a warmer world is a negative feedback that proceeds until forcing is negated. There is only one way to make sense of this - despite what #jiminys unnamed 'people' might think. This is such a simple and obvious thing that it illuminates a vexing dynamic. I have wondered at the reason for their aberrantly tenacious reiteration of error - almost inevitably spiced with disparagement or outright invective. Is it personality? Are they just those sort of people? Is it groupthink? Can they not admit error or uncertainty because it undermines the progressive - always with these AGW tragics - culture creating cognitive dissonance? Is it just that the group construct relies on being more moral and smarter than outsiders? Any concession to fallibility is the thin edge of the wedge? Is it all of the above?

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    Eh - 1000 GtC cumulative emissions is some 0.8 K warming - and with intrinsic centennial cooling kicking in through solar modulated wavy polar annular modes in the north and south - the real world response seems likely to be less. e.g. http://iopscience.iop.org/article/10.1088/1748-9326/6/3/034004/meta

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    This is the kind of confusion you get into with two definitions in your head that you can't distinguish from each other. Do you even know what the definition using the feedback loop and amplification factor is? I'm asking. Clue: It is in your Albany reference towards the end where they introduce positive feedbacks with an equation. Who are these people who talk about net positive feedbacks, you ask? Pretty much everyone. Who says a net positive feedback is actually a negative feedback? Just you.

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    We have had 1 degree C with about half that 1000 GtC, and a remaining positive imbalance meaning more to come from same.

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    Sum the IPCC feedbacks. Oh wait - they do it for you.

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    "We will call amplifying feedbacks positive and damping feedbacks negative." Agree? Do you see the difference from the definition that just uses λ? Definition 1: Based on the sign of λ. Net positive feedback impossible. Definition 2: Based on the amplification λ/λo. Net positive feedback possible. Feedback loop definition. Do you see that there are two separate definitions yet? Do you see that I have been telling you this all along?

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    Here's the IPCC figure they introduce. https://www.ipcc.ch/site/assets/uploads/2018/02/Fig9-43-1-1024x572.jpg "Legend: P: Planck feedback WV: Water vapor feedback LR: Lapse rate feedback WV+LR: combined water vapor plus lapse rate feedback C: cloud feedback A: surface albedo feedback ALL: sum of all feedback except Plank, i.e. ALL = WV+LR+C+A" Feedbacks are net negative - except when there are runaway ice sheet feedbacks. Is what they actually say.

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    ECS = ERF/ total feedback - see AR5 figure 9.43 for a net downward ERF and net negative feedbacks ECS is positive. "Things to note: The models all agree strongly on the Planck feedback. The Planck feedback is about λ0=−3.3 W m−2 K−1 just like our above estimate. The water vapor feedback is strongly positive in every model. The lapse rate feedback is something we will study later. It is slightly negative. For reasons we will discuss later, the best way to measure the water vapor feedback is to combine it with lapse rate feedback. Models agree strongly on the combined water vapor plus lapse rate feedback. The albedo feedback is slightly positive but rather small globally. By far the largest spread across the models occurs in the cloud feedback. Global cloud feedback ranges from slighly negative to strongly positive across the models. Most of the spread in the total feedback is due to the spread in the cloud feedback. Therefore, most of the spread in the ECS across the models is due to the spread in the cloud feedback. Our estimate of +2.0 W m−2 K−1 for all the missing processes is consistent with the GCM ensemble." The 'missing processes' are everything but the Planck feedback. All are simply additive and your definitions either spring from abject confusion or are intended to deceive and confuse.

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    Definition 1. Net positive feedback impossible. You keep saying this as though you have never heard of Definition 2 or the feedback loop concept.

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    The quote I gave about amplification comes from that same reference. He uses both definitions, but you weren't able to tell them apart. That article can confuse the unwitting which is why I called it sloppy.

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    Across 2 complete climate regimes in the last half of the 20th century - warming is negligible. https://watertechbyrie.files.wordpress.com/2018/12/cowtan-berkeley-e1545890023992.png

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    That seems to end around 2000. Using later data it looks like it gets more obvious. Undeniable even. http://woodfortrees.org/plot/best/mean:120/mean:240/plot/esrl-co2/scale:0.01/offset:-3.25/plot/sidc-ssn/scale:0.005/mean:80/offset:-0.6/mean:40/from:1850/plot/best/from:1988/trend

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    It has one simple meaning - consistent with the IPCC and Isaac Held you also called sloppy. Feedback is given in terms of W m^2 K^-1 - all of them. It may be either positive or negative - but is net negative except during glacial/interglacial transitions. The former is obvious the latter is something I have learned from the University of Albany - ATM 623: Climate Modeling lecture notes. Amplifying and damping can be seen in the simple formula for ECS. ECS = ERF/total feedback Gives an ECS of 2.5 K using the median values of Held/IPCC feedbacks. Positive feedbacks increase ECS and negative reduce it. Amplifying and damping. But these estimates are so uncertain and so incomplete that it remains a trivial exercise. One that $jiminy refuses to comprehend - or pretends not to.

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    Definition 2 you imagine and then give a fake math for - and the temperature feedback is the basis of black body physics.

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