Warming patterns are unlikely to explain low historical estimates of climate sensitivity

By Nic Lewis

Plain language summary

  • A new paper led by a UK Met Office scientist claims that accounting for the difference in the spatial pattern of surface temperature change between that in the historical period and that projected under long-term CO2-forcing substantially increases historical estimates of climate sensitivity. The claims are based on simulations by global climate models (GCMs) from the UK Met Office and three other institutions, driven by historical (last ~150 years) observations of sea-surface temperature (SST) and sea-ice.
  • The simulations show that the models’ effective climate sensitivity is substantially lower when driven by an observationally-based estimate of the evolution of SST and sea-ice over the historical period than when responding to long-term CO2 forcing. This finding underlies the authors’ conclusion that climate sensitivity estimates based on observed historical warming are too low.
  • The sensitivity of the results to the data used was tested by repeating the simulations by the two UK Met Office GCMs using a more recent SST and sea-ice dataset – an updated and improved version of the dataset that provided the sea-ice data used in the original simulations. The results, which appeared in the paper’s Supporting Information but were not reported in the paper itself, were completely different.
  • The divergence between the simulation results presented in the paper itself and in its Supporting Information show that the authors’ key claim, that climate sensitivity estimates based on observed historical warming are too low, are highly sensitive to the SST and sea-ice dataset used. Results using the more recent dataset contradict their claims, largely due to differences between the two datasets in the evolution of sea-ice more than counteracting the effects of evolving patterns of SST change over the open ocean. I therefore think it is difficult to draw any strong conclusions from the simulation results presented in the paper.
  • Moreover, the study conflates two different temperature-change pattern effects, both of which affect estimated climate sensitivity in GCMs:
  1. that arising from the difference between the simulated spatial pattern in response to long-term CO2-forcing and the spatial pattern simulated  when GCMs respond autonomously to evolving forcing over the historical period; and
  2. that arising from the difference between the spatial pattern over the historical period simulated when GCMs respond autonomously to evolving forcing and the spatial pattern when they are driven instead by a specified, observationally-based, evolution of SST and sea-ice, with unchanging forcing.
  • The first pattern effect concerns forced changes and has been shown to lead to modest (~10%) underestimation of estimated equilibrium climate sensitivity (ECS) for typical current generation GCMs (range -10% to + 50%)[1], although two published studies incorrectly claimed that the effect was much larger.
  • The second pattern effect is only relevant to observational estimation of climate sensitivity to the extent that it is caused by natural climate system internal variability. That extent cannot be major – contrary to what the new paper implies – if current GCMs realistically simulate climate system internal variability. All or part of the second pattern effect might instead be attributable to GCMs incorrectly representing historical forcing and/or the climate system’s response thereto, and/or to inaccuracies in the observational SST and sea-ice dataset used.


Soundly-derived recent estimates of effective climate sensitivity (EffCS)[2] based on observed warming over the historical period, EffCShist, have generally been in the 1.6–2.0°C range. That is well below EffCShist estimates for general circulation models (GCMs, also called global climate models) driven by historical forcing, which for current generation (CMIP5) models average 3.0°C (Lewis and Curry 2018).[3] Those estimates are for GCMs with their atmospheric model coupled to a 3D dynamic ocean model (AOGCMs).

A new paper (Andrewsetal18)[4] compares “amipPiForcing” simulations by six AGCMs (the atmospheric model components of AOGCMs) with CO2-forced simulations by their corresponding AOGCMs.[5] Two of the AGCMs used were developed at the UK Met Office – where the lead author works – and the remainder at three other modelling centres. Almost all the simulation results have been published previously; this paper brings them together and makes comparisons.

Figure 2. EffCS estimated from HadGEM2 simulations using OLS regression. Black-filled circles show means for years 1-50 of the HadGEM2-ES abrupt4⤬CO2 simulation, grey-filled circles those for years 51-150. Values derived from the abrupt4⤬CO2 simulation have, as is usual, been halved to give estimates of F2⤬CO2 (from the y-intercept) and EffCS (from the x-intercept).

Full story on Climate Etc.

46 thoughts on “Warming patterns are unlikely to explain low historical estimates of climate sensitivity

    • “Why are all these people working with GCMs …”

      I dunno. Maybe because working with GCMs is what they do. It’s not like a career working with GCMs qualifies one for many other jobs.

      I’m a bit curious where they found historic SST and sea ice data beyond about 40 years that is remotely usable..

    • “It is difficult to get a man to understand something, when his salary depends on his not understanding it.”
      ― Upton Sinclair

    • GCMs are wrong because the data is poor. The best model in the universe produces poor results if fed poor data.

    • “Why are all these people working with GCMs” –

      leave’em their GCMs / no other tools thei’re aqquainted with / they ever held in hands.

  1. I’m sorry but I find this very confusing. Perhaps someone can help? Is the Met Office guy saying that the observed historical data must be wrong because his models say so? That would, surely, be a ludicrous conclusion, presumably designed to create more Adjustocene fun.

    • It’s confusing for sure.

      What the Met Office scientist is doing looks more like hacking than it looks like having a deep understanding of what’s actually going on.

      Nic points out that the supposed effect goes away when newer data is considered. That indicates that the paper’s findings are far from robust, to say the least.

      Kudos to Nic Lewis for wading through that crap.

        • Just an aside – are you the Vukcevic who used to post on solarcycle24 years ago?

          If so, thanks for your work back then – it helped me refine my disgust with the AGW crowd. 😀

    • ” …The results, which appeared in the paper’s Supporting Information but were not reported in the paper itself, were completely different. ”

      It’s not clear who is talking or what the point is. If I re read it enough it might make sense.

      I’ve re read it several times now. Nope. I agree Ian.

      • I believe those are Nic’s summary points of the paper that are related to his post. What (imo) he is saying is that they make claims in the paper that are not really supported when you read THEIR OWN “SUPPORTING INFORMATION” that is published online but not in the paper itself.

        • to paraphrase, “If you have to explain it to me, I won’t understand it”.
          I’m reading this article and I’m thinking, ” What ?????????, is there a smoking caterpillar somewhere? “

  2. Thus proving the MET doesn’t really do science, just scaremongering activism.
    Privatise the whole rotten edifice.
    Put it on eBay with a £0.99 reserve. There will always be a mug somewhere with a pound to waste.

  3. “Chinese cargo ship conquers Arctic route”
    Surprise, surprise, Chinese ice breaker makes it [through] the Arctic ice in September when the ice extent is at its minimum.
    “The route has opened up because of global warming; Beijing has sent freight ships through the North East Passage before but the Tianen is its first with built-in ice-breaking capabilities.”

    • The Siberian coastal Northern Sea Route was open in the 1930s and ’40s, as well, and not just to icebreakers. It played a role in WWII.

      • Absolutely correct. There was less Arctic ice during WW2 than there is now. The logs and reports of warships operating up there still exist in various archives and prove it absolutely.

    • No big deal!


      A small wooden ship, the St. Roch, sailed through the Northwest Passage and across the high Canadian Arctic twice, in 1942 and 1944. Try doing that today.

      These voyages followed soon after the global warming period that ended circa 1940. What was the ice extent and thickness then? Probably less than, or no greater than today.

      Starting one’s graph on Arctic ice extent in 1978, after the ~35-year global cooling period from ~1940 to ~1975 is dishonest – “loading the dice”, a standard tactic of global warming fr@udsters.


      • Exactly Allan! The alarmists must hate having history and facts thrown at them…but they seem to have no shame at all! They just move on to the next lie or exaggeration.

        • All true Al – telling big lies about anything and everything is what the left does best – in fact it’s the only thing they do well.

          The left gets elected by appealing to the stupidest and laziest people in the country, and promising them a whole lot of free stuff. Then the country goes to hell, like Zimbabwe, Venezuela and so many others.

          The left has proved time and time again that they cannot run a country – except to run it into the ground.

      • A “small wooden boat”? Actually an ice-fortified, 31.2m (104ft) long schooner built from extra-thick timbers of Douglas Fir, sheeted on the outside with Australian “Ironbark” Eucalyptus Gumwood, one of the hardest woods available. It also has a steel plate covering a very sharp Bow.
        As for those sailings, the first voyage took about 28 months (850 days), between June 23 1940 and Oct 11 1942, and the second a total of 86 days (from July 22 to Oct 16 1944).

        Skipper Larson’s description of those seasons? “The three seasons of the short Arctic Summers from 1940-42 had been extremely bad for navigation, the worst consecutive three I had experienced as far as ice and weather conditions were concerned, and in my remaining years in the Arctic I never saw their like. Without hesitation I would say that most ships encountering the conditions we faced would have failed. I also believe that had we missed the single opportunity we had to get out of Pasley Bay, we most certainly would still be there, in small bits and pieces.”

        And that second, shorter voyage? Larsen wrote that that particular season was “the worst in years.”
        Doesn’t sound so easy, does it? Not like nowadays, anyway.

  4. I only wish the climate model auto-erotica simulators could provide such “accuracy” in predicting the weather for my daughter’s upcoming outdoor wedding in mid October. Will it be an Indian, er, First Peoples Summer? Or Polar Vortex nightmare?

    Knowing this could save ME almost as much money as is being spent on the Climate Change hoax.

    • Kenji
      lf you live in England and the wedding is on the 18th October then the odds are good that it will be a decent day weather wise.

      • I would have quite enjoyed living in England in the early 1960’s … when it was still … England. Now? I’d have to find a shire that hasn’t been overrun by the interloper’s cultures.

    • My daughter got married on Saturday July 28th.
      These were the CET max temperatures
      26 30.7
      27 29.7
      28 20.3
      29 21
      30 22.4
      I arranged for a sudden drop in the temperatures so the ladies would be comfortable in their special occasions finery and the elaborate hats and gentlemen could turn up in suits rather than the short sleeve shirts.

  5. “The simulations show that the models’ effective climate sensitivity is substantially lower when driven by an observationally-based estimate of the evolution of SST and sea-ice over the historical period than when responding to long-term CO2 forcing.”

    So when they plug measurements into models, the climate sensitivity is lower than when they use models alone.

    They conclude:
    “This finding underlies the authors’ conclusion that climate sensitivity estimates based on observed historical warming are too low.”

    Say W.H.A.T.? The proper conclusion is that the GCMs don’t work, not that the observation based sensitivity is wrong. This passes for “science” today? Laughable.

    • I’m glad that I’m not the only one who interpreted their assertion that way. Reality isn’t matching our model… something must be wrong with reality. Where is Josh Willis? Quick, man, find a couple of data points to remove!

    • My face twisted in confusion, when I was reading that sentence too. Let me focus on it again:

      “The simulations show that the models’ effective climate sensitivity is substantially lower when driven by an observationally-based estimate of the evolution of SST and sea-ice over the historical period than when responding to long-term CO2 forcing.”

      (1) Okay, let’s drive the models with “observationally-based estimates of SST and sea ice …”
      (2) Now observe the models “responding to long-term CO2 forcing”.

      I don’t get it — the forcing to which the models are responding is already built into the models, right? So, how does comparing OBSERVATIONALLY-based estimates to already-built-in biases prove a damn thing? — other than the models do NOT respond to OBSERVATIONALLY-based, real-world estimates the same way that they respond to already-built-in biases?

      Or, do I have the totally wrong take on this statement?

  6. “The claims are based on simulations by global climate models (GCMs) ”

    Stop the presses! Bullsh!t Alert!

    GCM’s? Really? Try Solar Power – stick ’em where the Sun don’t shine!

  7. This is simply climate science modelling speak.

    My plain language summary:

    Nic Lewis’s analyses just shredded the Met Office’s attempt to justify their continued higher 2xCO2 climate sensitivity estimates from the GCMs. Nic turns on the lights to the pool, and the Met Office is caught swimming naked … once again.

  8. Do these models account for the resistance of the system to change a la Le Chatelier principle – the temperature homeostasis effect of evaporation, convection, clouds, winds, currents, rain, snow, albedo changes….The CO2 forcing, should have a coefficient <1 (possibly 0.33 given the couple of hundred percent overestimate of projections over 40yrs).

  9. I wonder which bit of the carefully selected past they claim shows climate sensitivity is greater than we all think? Could it be when CO2 levels ran at 5 or 6,000 ppm? In which case an explanation of why the runaway Venus greenhouse didn’t happen might have been an interesting and necessary clarification. Otherwise, I am going with the general view expressed here of ho, hum another self-serving give us more money, worship, etc etc.
    That’s the trouble, when you keep exaggerating, fiddling data, claim false record heat and all the rest of it, sane people stop believing your lies.

  10. Put poor data into any model and all you can get is poor results. Models cannot solve or prove anything – they just model your assumptions. That is what they are modelling – reality doesn’t somehow magically enter a model.

    You literally cannot get good data from a model fed poor data.

  11. Wait…

    So observationally-based sensitivity disagrees with the models so they run more model data to show the observations, i.e. the actual REAL world, is wrong and their computer GIGO products are correct?

    Shouldn’t SCIENCE decide that the observations prove the whole CO2 fantasy is BS and they need to return to basics?

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