John Hartz says: May 4, 2018 at 6:44 pm
“Back to basics: Climate Sensitvity (CS) is an index created to compare model runs. It is model output, not a model input.”
Dave_Geologist says: April 27, 2018 at 2:43 pm
” Dessler’s point AFAICS is that if you take a suite of physics-based models, where you know the ECS in advance, and try to calculate it the way LC13 and LC18 do, you get the wrong answer.”

The old chestnut, Lucia [whom I trust] used it as well, is that ECS is an emergent property of climate models. The truth is that the ECS is hardwired into all the GCM.
At around 3C.
Put 3C ECS in and 3C ECS comes out.
Compare it to the real world, the only one, where 3C rarely comes out unless you pick exact time frames of extra warming like a decade ending in a large El Nino.

Consequence is shadow boxing, dodging the real questions and answers.
Dessler is right but so is Lewis but on two different stages.
It is so easy to answer a question on the first stage show in the second show arena.dikranmarsupial says: April 24, 2018
Even angech’s own sources refute him. His original claim was:
These can give an indirect record of past temperatures, but only locally. Such records indicate that Temperature changes equivalent to the modern 150 year warming have happened a number of times in the past 3000 years. [emphasis mine]
and he supports that with:
“The NRC committee stated that “The basic conclusion of Mann et al. (1998, 1999) was that the late 20th century warmth in the Northern Hemisphere was unprecedented during at least the last 1,000 years. This conclusion has subsequently been supported by an array of evidence that
includes both additional large-scale surface temperature reconstructions and pronounced changes in a variety of local proxy indicators”
and says: This basically agrees and supports what I have said. There are possible higher and lower spikes in the temperatures in the past that do not show because of “the wide error bars” as one goes backwards and the “uncertainties inherent in temperature reconstructions for individual years and decades are larger than those for longer time periods’.

DM “Err, no it doesn’t, it says that the recent warming is unprecedented.”

Having been called out in the past for not fully quoting comments I guess I can do a tu quoque?
The NRC did not say “the recent warming is unprecedented.” Mann et al said that.
The part that DM leaves out says clearly plausible only with substantial uncertainties before 1600.
I will append the bit he missed by accident.

“Based on the analyses presented in the original papers by Mann et al. and this newer supporting evidence, the committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium”, though there were substantial uncertainties before about 1600?”.

“Note also the goal-post shift from “have happened” to such spikes being “possible”, without acknowledging the weakening of his position. Rather shabby.”

Sorry DM I have not changed my position. No goal post shift. Read my comment again noting “have happened” refers to events ” past temperatures, but only locally” which are well known and real.
The ”spikes” being possible refers to the separate concept that such temperature spikes may have been general rather than local and would not be visible due to the large error range in time and temperature.
Good try.


  • BBD says:

    I would like your opinions on the statistical probability of such events existing [my statement] rather than sidetrack to the question of how as you have an excellent understanding of the statistics involved.

    If no plausible physical mechanism exists that could produce a global warming of ~1C and ~150y in duration, there is nothing further to discuss.

    Since you cannot (will not) answer this question, I’d say we are done here.

  • angech says:

    Your comment is awaiting moderation.

    izen says: @-metzomagic
    “What physical process could possibly produce a 1 deg C spike in temperatures that disappeared without a trace within a 200 year time span?”
    It is a good question.
    A short global warming of similar magnitude to the present would need a large-scale cause.
    Solar variation.
    A large methane ‘burp’
    Albedo changes from massive global ice cover loss.”
    I could add
    Albedo changes from vegetation color changes,
    Algal or jellyfish sea plumes,
    widespread black soot deposits from a massive volcanic explosion/s,
    Prolonged excessive cloud formation,
    Two very large volcanic explosions 200 years apart.
    Recurrent runs of large El Nino events.
    or a combination of these events on smaller scales.
    A combination of several events might nudge the plausibility barrier.
    Two very large volcanic explosions 200 years apart would certainly do it but is not fair.
    I doubt that warming are only possible from massive global ice cover loss. All the ice one needs for evidence has melted.
    You have shown that some of the first scenarios lack the proof that would be needed for attribution. Most of the others should also have left some traces.
    “a lack of inevitable effects.
    We know what effects the current rapid warming has had. It is inevitable that any similar energy gain in the past would have the same effect. AFAIK there is no evidence that there was a similar sea level rise in the Holocene since the end of the de-glaciation.”
    Good point.

    I suspect if there was it would show up in the timing and observable locations of solar and lunar eclipses.
    Too esoteric for me

    “Otzi the ice man would have defrosted in any previous rapid warming as glacier mass balance shrinks. ”
    Depending on whether he fell in a crevice at the start or the end of the glacier, surely? And how long and big it was.

    “While the proxies may theoretically be able to miss a short spike in the Holocene, there are other reasons to doubt it could happen and not be evident.”
    Perhaps this quote rebuffs your very good quote
    The absence of evidence is not evidence of absence.

     Look, I think the piling on is really healthy, happy to wear it and argue it to the hills, but only with the lighter weights.
    I want to avoid a Dikran vs angech comment thread, at all costs. I think Dikran’s point of view is explicit, and clear and totally different to mine.
    He is a lot more entitled to his views due to his senior status here and his scientific knowledge and expertise.
    That is not to say that I will not put up an alternative point of view and and discuss it with the rest of you if you address the same arguments.
    ATTP’s point
    “It’s almost 20 years since the publication of the first hockey stick paper (Mann, Bradley & Hughes 1998). The hockey stick refers to millenial temperature reconstructions that look a bit like a hockey stick; a period of centuries during which temperatures appear reasonably flat, or cool slightly (the shaft), followed by a period of rapid warming starting in the mid-1800s (the blade)”
    is something I concur with.
    I point out, mathematically why this must happen with any older proxy record.
    I point out that the standard deviations grow as we go back in time and are large enough to easily encompass 1C ranges of temperature for 150 years without it having to trouble the records.
    It cannot trouble the records because the SD is much larger than 1C.
    So why the fuss?
    Why do we have to say the past 3000 years ran along with nary a squeak off the railroad straight hockey shaft?
    Internal variation too large lets denialists claim a slight risk to the scientific consensus?
    Even though when we admit it is large enough short term we can show observational ECS is too low?
    Not my problem, nor yours either if you man up to the scientific facts and work with them.
angech says:

Your comment is awaiting moderation.

The atmosphere seems to have changed a little here since the publication in a journal of this reputable paper. Or was that the publication in a previously respectable journal of this paper?
Good to see nobody arguing that it need more peer review or the editor should be sacked for letting it through with pal review.
And even better that 1.6 C now seems to have become an acceptable lower limit [not an accepted true value] instead of the cries of it must be above 2.0C.

I missed this comment by DG though Mosher did pick it up.
Kudo’s Mosher.
Dave_Geologist says: April 27, 2018 at 2:43 pm
” Dessler’s point AFAICS is that if you take a suite of physics-based models, where you know the ECS in advance, and try to calculate it the way LC13 and LC18 do, you get the wrong answer.”

Did you really mean to say that Dave?

angech says:

Your comment is awaiting moderation.

dikranmarsupial says: May 1, 2018 at 3:19 pm
angech, don’t change the subject, provide evidence to support your claim that “observations are falling badly behind computer model predictions of what the temperature rise should be.”

At last I can be helpful. evidence from an expert.
”More about Equilibrium Climate Sensitivity” earlier ATTP post
“Andrew Dessler @AndrewDessler 14 Dec 2017
Terrific session on climate sensitivity today at #AGU17. Lots of discussion about climate sensitivity (ECS) estimates from the 20th century. The problem is that estimates of ECS from the 20th century obs. record are lower (1.5-2°C) than models (3°C).”

and Andrew Dessler says: April 27, 2018 at 2:51 pm
“According to our model ensemble, 155 years is not enough to eliminate the impact of variability on the estimate of ECS. Also, you asked how internal variability could’ve turned out differently. Well, that’s exactly what our model ensemble tells us. And the answer is that it can turn out differently enough to confound our estimates of ECS.”

…and Then There’s Physics says: April 28, 2018 at 10:42 am
“”as Andrew Dessler indicates – if you do consider GCM results, they suggest that these observationally-based, energy-balance approaches tend to be biased low. “


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