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In 1997 he put the 2xCO2 sensitivity at 0.3-0.5C (see Lindzen 1997). There is some equivocation in the paper above, but it sounds like he is now entertaining a value on the lower end of the IPCC range at about 1.5C. The rate at which his estimates have increased is about +0.45C/decade...faster than the actual warming rate. I will say that at least Lindzen proposes a legitimate hypothesis for supporting lower climate sensitivities...the iris effect. The question is...does Earth really have a mechanism like this that makes it resistant to climate change? The paleoclimate record seems to suggest that the Earth is quite amendable to large changes given the proper nudge and with each passing decade in the contemporary warming era we are constraining the lower the bound of sensitivities to higher and higher values. Each passing decade of warming is making Lindzen's iris effect and change resistant hypothesis appear less and less likely. BTW...A recent comprehensive style study puts the range at 2.6-3.9C and 2.3-4.7C for 1-sigma and 2-sigma confidence respectively (see Sherwood 2020 and free). Also, I just want to say that I do not condone the tone and rhetoric used against you. I do not think you are a liar, troll, or Russian (not that nationality matters). And while I do not think the body evidence supports the position you advocate for I still think you've handled yourself respectfully nonetheless. I think if you and I sat down for a beer (or coffee) we'd probably get along just fine. I still think you're wrong about climate science though

Here is Dr. Alley's data: ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/isotopes/gisp2_temp_accum_alley2000.txt Notice that the rate of warming today is unprecedented during the Holocene per Dr. Alley. The warming rate is so high today that it smashes the record from that noticeable blip from 8210-7820 that admittedly looks pretty robust at first glance. The problem is that the x-axis on this specific graph has non-linear scaling (who does that?) and it is missing the contemporary warming era. This graph ends in 1855...a full 165 years in the past. If you stich on the last 165 years of warming we are at least close to the peaks of the Minoan warm period and Holocene climate optimum in the best case and may have already popped the bounds of the y-axis in the worst case. BTW...here's a good lecture by Dr. Alley if you want to hear his take on the science.

I was going through my Parametrization Schemes book by David Stensrud to try and better understand how GCMs handle water vapor. It's pretty complicated. Quite frankly...over my head. But I do see that many of the physics modules use the Clausius-Clapeyron and other relationships. I think if there was anything wrong with our understanding of the thermodynamic nature of water vapor and associated feedbacks then it would have had an impairing effect on weather forecasts and would have been noticed long ago.

It is an amplifying feedback only. It is included in the chart implicitly. For example, the total anthroprogenic RF of 1.0 W/m^2 includes the amplifying effect of water vapor. When the water vapor feedback is included it is called effective radiative forcing (ERF). AR5's convection is to use solid bars for ERF. The best analogy here are audio amplifiers. There are many agents that can catalyze a sound: drummer, guitarist, vocalist, etc. Each agent has their effect amplified by the same fixed amount, but the amplifier does not catalyze a sound on its own. The final noise level is a product of all individually amplified agents. Like with climate forcing agents it is convenient to quantify each noise forcing agent's contribution to the final sound output with the amplification factor already included.

How do you know General Relativity is correct? It is but a model of gravity. I believe that model is correct because it makes predictions of the precession of Mercury, time dilation of the GPS satellites, etc. that match observations within a reasonable margin of error. It is the same with the consensus theory of climate change. We believe the models are correct because they makes predictions that match observations within a reasonable margin of error. The natural-only or natural-mostly hypothesis makes predictions that deviate from observations by an unacceptable amount. The predictions are bad enough that they are off by an order of magnitude in predicting the EEI at least after 1950. In fact, they are so bad that they often cannot even predict the sign of the temperature change. Ya know...I'm skeptical of quantum mechanics and general relativity. Between the two they make what is often called the worst prediction in all of science regarding the cosmological constant. One or both of them is wrong by an amount so astonishing that we cannot even fathom it. But I still think QM and GR are useful and they are certainly better than nothing. The same can be said for the consensus theory of climate change. The models deployed are not perfect. They never will be. But they are undeniably useful and represent the best of what we have. It is okay to advocate for natural-only or natural-mostly models for the post WWII era. But to convince cranky skeptics like me to use them in favor of what is already available you have to demonstrate that 1) they are testable, 2) they make useful predictions, and 3) that they match reality better and/or are simpler in answering certain questions than what we already have.

I'm sure there has been a positive energy imbalance since 1800. The question is...what contributing factors caused the imbalance and how and when did their contributions ebb and flow? Some of the warming is natural especially prior to 1950. But after 1950 the net of all naturally modulated factors is far too low to explain the warming. It is so low, in fact, that naturally modulated factors may even be working to lower the EEI and thus put a cooling pressure on the climate. But when scientists consider anthroprogenically modulated factors along with the naturally modulated factors we get a reasonable match between expectation and observation. Anthroprogenic factors dwarf natural factors by about an order of magnitude...at least after 1950 when the warming became most acute. We've already had about 1.2C of warming since about 1850 and that's with about 1.5xCO2 and a +0.87 W/m^2 EEI that still hasn't equilibrated yet. Even if CO2 concentrations stabilized at the current 410 ppm level we still have several tenths of degree C to warm to work off that EEI and measure the ECS. So the question for you is this...if CO2 is only 1/3'ish effective as the consensus then where are you going to get the other 2/3 energy required to produce the amount of warming we observe?

Even Arrhenius understood the water vapor feedback and considered it in his primitive 1896 model. The ERA5 850mb data is intriguing indeed. I'd like to learn more about this decline. I'm not as ready and willing to chalk up things I don't understand to the inadequacies of the data. ERA5 is considered to be the best of the best. I'll see if I can do some digging on that 850 mb specific humidity decline from 1980-2000.

I'm just being pedantic here...the word "runaway" actually has special meaning in climate science. It is unlikely that Earth can achieve "runaway" greenhouse warming in the strictest sense. This is due primarily because the Simpson-Nakajima limit (and related Komabayashi-Ingersoll limit) on Earth is sufficiently high and because the primary feedback driver would be water vapor which is a condensing gas. The SN limit is the clamp on the outgoing longwave radiation (OLR) in a saturated atmosphere. The SN limit is thus the point at which absorbed solar radiation (ASR) must exceed OLR to bootstrap the runaway phase. I believe the SN limit is around 290 W/m^2, but OLR is currently 240 W/m^2 so there is ~50 W/m/2 of buffer before the SN limit is even reached. The consensus seems to be that there aren't enough non-condensing GHGs to get us anywhere close to this SN limit. However, a "moist" greenhouse has a lower limit. The moist greenhouse is characterized by a state at which the Earth's cold trap near the stratosphere can no longer stop the leaching of water vapor (which would typically condense out and drop back to the surface) into the stratosphere where it would then slowly deplete to space. Aside from the obvious fact that the atmosphere would be in a perpetual moist state this scenario would likely have other undesirable consequences like the destruction of the ozone layer and evaporation of the oceans. There is still considerable debate regarding whether Earth can support a moist greenhouse state. Assuming that it can the estimates I've seen of the CO2 required to bootstrap this process could be 10,000 ppm (give or take) given the current solar output. I will add the caveat that there are notable scientists (namely James Hansen) that aren't quite so confident that a "runaway" phase is not achievable. Here is a pretty good summary style publication that explains things better than I can. Goldblatt & Waston 2012: The runaway greenhouse: implications for future climate change, geoengineering and planetary atmospheres

That first paper says the water vapor feedback is strongly positive at about 2 W/m^2 per C. They end with "The existence of a strong and positive water‐vapor feedback means that projected business‐as‐usual greenhouse‐gas emissions over the next century are virtually guaranteed to produce warming of several degrees Celsius." Unfortunately the second paper is paywalled and I cannot find an open copy. I will say that I took the opportunity to read other publications by the lead author Dr. Sullivan. So far I've not seen anything that leads me to believe he doubts the water vapor feedback or GHGs contribution to warming.

Ok, but an out-to-sea in the North Atlantic solution "makes sense" as well. Making sense doesn't mean it's right. I will say that given the relatively tight spread (given the circumstances here) of the EPS members I'm certainly not going to blow off the possibility of a Sandy-style left hook. In fact, given that a few members of the CMC and UKMET ensembles also show the tug back westward I'd actually give this possibility some well earned weight. We'll see happens.

The difference between the ECMWF and the GFS/UKMET/CMC regarding the upper level pattern are striking. Will it pull off another coup or will it flop?

UKMET says it may do something as well.

I agree. I think the aerosol hypothesis can be at least partially falsified by the OHC data. If aerosol increases were playing a significant factor we should have observed a decrease in the EEI and thus a reduction in OHC uptake. I think ENSO or other natural cycles better explain the atmospheric warming hiatus. Cryosphere declines also seem (to me) like a reasonable hypothesis for explaining the hiatus as well, but I haven't seen any literature that I can use to support it at the moment.

Right. No disagreement with the uptake of carbon by the ocean. But oceanic heat content (OHC) is a measure of heat uptake; not carbon uptake. It is directly related to the Earth Energy Imbalance (EEI). The EEI is dispatched into the ocean, air, ice, and land. The hiatus period is characterized by a general pause in heat uptake by the air despite heat uptake proceeding in the ocean. ENSO cycles likely played a role in the waning of the transfer of heat to the atmosphere. I was wondering how much of a role the cryosphere played in that as well. The puzzle is that increased aerosol loading brings down the EEI and thus should have reduced the rate of OHC increases. This is what makes me think aerosol loading may not be as important in explaining the hiatus period as some have hypothesized. @donsutherland1 found the following study which estimates that value at 89%. It appears to be one of those comprehensive style studies that attempts to provide the best estimate of EEI with the lowest uncertainty from the vast body of evidence available at the time of publication. Schuckmann et al. 2020: Heat Stored in the Earth System: where does the energy go? There are some big names in the author list and the bibliography at the end is huge. Keeping in mind that I'm but an amateur...this looks like something that will be heavily relied upon in the upcoming IPCC AR6 report.

Aerosol loading probably explains part of the warming hiatus. One thing that puzzles me is that oceanic heat content kept marching upward. It makes me wonder if the typical transfer of heat into the atmosphere waned during the period only to be taken up by the cryosphere. The post 1998 El Nino period was about the time where cryosphere declines became most acute.