1D Model of Global SST Shows 40% of Warming Since 1979 Due to Early Volcanic Cooling

January 14th, 2020 by Roy W. Spencer, Ph. D.

In 2017, Christy & McNider published a study where they estimated and removed the volcanic effects from our UAH lower tropospheric (LT) temperature record, finding that 38% of the post-1979 warming trend was due to volcanic cooling early in the record.

Yesterday in my blog post I showed results from a 1D 2-layer forcing-feedback ocean model of global-average SSTs and deep-ocean temperature variations up through 2019. The model is forced with (1) the RCP6 radiative forcings scenario (mostly increasing anthropogenic greenhouse gases and aerosols and volcanoes) and (2) the observed history of El Nino and La Nina activity as expressed in the Multivariate ENSO Index (MEI) dataset. The model was optimized with adjustable parameters, with two of the requirements being model agreement with the HadSST global temperature trend during 1979-2019, and with deep-ocean (0-2000m) warming since 1990.

Since the period since 1979 is of such interest, I re-ran the model with the RCP6 volcanic aerosol forcing estimates removed. The results are shown in Fig. 1.

Fig. 1. 1D model simulation of global (60N-60S) average sea surface temperature departures from assumed energy equilibrium (in 1765), with and without the RCP6 volcanic radiative forcings included.

The results show that 41% of the ocean warming in the model was simply due to the two major volcanoes early in the record. This is in good agreement with the 38% estimate from the Christy & McNider study.

It is interesting to see the “true” warming effects of the 1982-83 and 1991-1993 El Nino episodes, which were masked by the eruptions. The peak model temperatures in those events were only 0.1 C below the record-setting 1997-98 El Nino, and 0.2 C below the 2015-16 El Nino.

This is not a new issue, of course, as Christy & McNider also published a similar analysis in Nature in 1994.

These volcanic effects on the post-1979 warming trend should always be kept in mind when discussing the post-1979 temperature trends.

NOTE: In a previous version of this post I suggested that the Christy & McNider (1994) paper had been scrubbed from Google. It turns out that Google could not find it if the authors’ middle initials were included (but DuckDuckGo had no problem finding it).


56 Responses to “1D Model of Global SST Shows 40% of Warming Since 1979 Due to Early Volcanic Cooling”

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  1. DR Healy says:

    Great post, thanks. Also ironic in that it follows the same pattern of adjusting past temperature lower to create to create a stronger upward trend as has occurred in the surface temperature record.

  2. Craig T says:

    What were the results of running the model from 1900 to present without volcanic cooling?

  3. Scott R says:

    Dr Spencer,

    You have cleverly separated out the volcanic forcer from 1980-present, but how about the AMO? Surly that had an effect as well. How about the increase in zonal air flow? That seems to lead things higher as well. What percentage of the warming from GHGs were from water vapor? Have you ever constructed a pie chart of all the forcers and their amplitudes as a percentage of the total 1980-2020 trend? I’m very interested in your thoughts.

    • In order to account for the AMO, I would need quantitative evidence that it changes the global radiative balance, like I have done for ENSO. That takes time. ENSO is the largest source of natural climate variability, with clear signals in the data, which is why I started with that.

      • Scott R says:

        I found cycles of 60 years, 84 years within the AMO. It means every 360-420 years the cycles can interfere and drop the AMO a lot.. seems solar forced, timed to great conjunctions. I really think this is an important task, trying to confirm this.

        Check out the zonal vs meridional flow… 60 year cycle. Drought in Australia? 60 years. As we climb the AMO cycle, we add water vapor… that warms, but it charges the drop as clouds cool once it condenses. (Reflects from snow too) I think of the earth as a 2 mode system… bouncing back and forth between equilibrium levels set by many forcers.

    • Richard M says:

      As far as I can see the biggest influence of the AMO comes from pushing warmer water into the Arctic. The resulting loss of sea ice allows a lot of warming of the air and release of water vapor. This drives up Arctic temperature which is then a positive feedback resulting in even more loss of ice.

      In this chart you can see the effect take off around 2003. The AMO went positive sometime in early or mid 1990 so there was a considerable lag before we saw the effect. It also appears like it increased with the 2016 El Nino.

      http://www.woodfortrees.org/plot/hadsst3nh/from:1997/to/plot/hadsst3sh/from:1997/to/plot/hadsst3sh/from:1997.5/to:2015/trend/plot/none

      If you look at any of the global temperature charts you will see most of the warming is in the northern areas. This explains that variation better than any other explanation.

      So, how much of the warming over this 40 year period is due to the AMO? Could be 100%.

  4. Bindidon says:

    It is always amazing for me to look at comments telling us that if the volcanoes hadn’t erupted, the past would be warmer and thus the trend lower.

    As if the trend was in their life the only thing that would matter ever.

    The trend would have been lower as well if the two big El Ninos wouldn’t have happened, and of course higher without the La Ninas these people always ‘forget’.

    This means that
    – either you keep the UAH temperature series as it is,
    – or you remove all volcano and ENSO signals.

    Exactly that was done by Grant Foster and Stefan Rahmstorf for surface series,and by Santer, Bonfils & al for the lower troposphere.

    The latter group used in 2013 RSS3.3 which has been nearly identical to UAH6.0.

    Their result: the residual trend after removal was about 0.09 C / decade (for 0.124 C for the original data).

    Exactly that you would obtain with UAH6.0 LT…

    • Richard M says:

      Bindidon, the objective is to understand how much warming has occurred over the past 40 years. This will give us a handle on climate sensitivity. If noise is included in the calculation then it will obviously be wrong. I think it is hilarious you want a wrong answer.

      I made a comment many months ago where I did something very similar to what Roy did here. I simply eliminated years/months that had a large influence of non-climate factors. When I looked at the difference I found .26 C of warming between 1980 and 2018.

      Of course, I was attacked for cherry picking. And, I was. I was trying to cherry pick the periods where we had a true climate signal. Amazing how many of the alarmists wanted nothing to do with that information.

      You are showing your true colors. You really do not want to know what is happening.

    • Bindidon says:

      John Bills

      Look at the link in the comment above yours, it is free to access, and by far more complete than the official article behind paywall (I have it too).

    • Steve Case says:

      strop says:
      January 15, 2020 at 7:25 AM
      A Graphic Account Of The Climate Crisis

      Great You Tube – too bad comments are turned off.

  5. E. Swanson says:

    Dr. Spencer, Your analysis compares measured ocean thermal energy content between 60N and 60S with depths to 2000m. However, in the real world, the lower depths of the oceans are continually being re-supplied with very cold waters from higher latitudes, both in North Atlantic and Arctic Oceans and in the Pacific around the Antarctic. In other words, the THC re-supply may be producing less warming at intermediate depth, therefore the actual energy flow may be greater near the surface to offset this cooling influence.

    Also, we know that over a year, the polar regions emit more LW energy than they receive from the Sun as SW, the difference being made up via transport of sensible and latent energy in the atmosphere and also via ocean currents. Limiting the latitude under consideration will ignore these extra energy emissions. Does your 1-D model account for this energy loss?

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  7. Mike Roberts says:

    Just to be clear, you’re taking a 40 year data series from a model, which gives only SSTs (which are warming more slowly than the land), then estimating the impact of volcanoes on those data to determine that humans have been responsible for the lion’s share of the warming we’ve seen since 1979?

    I think most other climate scientists would agree that human behaviour is the primary factor in global warming but I’m sure that the actual contribution on surface temperatures is better estimated using actual data, preferably from a longer period, for the whole globe, as much as possible. Didn’t the IPCC do that and estimate the human contribution to warming since 1950 as greater than 100% (with other factors having a slight cooling effect since then)?

  8. Bindidon says:

    Richard M

    “So, how much of the warming over this 40 year period is due to the AMO?”

    Could be… zero dot zero %.

    Not only are you totally fixated on your AMO baby; you furthermore still are, as you noted yourself somewhere above, a grand-maitre [surtout pas d’accent circonflexe ici!] in the wonderful world of cherry-picking.

    Hence, instead of considering AMO and SSTs over a sufficiently long period, you reduce that period to a strict minimum fitting to your little satellite era narrative.

    But even before understanding the necessity to have a wider-angle look at SSTs, a person with a sound relation to Earth would first compare the two Hemispheres in a geographic sense, and note that

    – (1) while the NH mainly consists of an ocean surrounded by huge land masses, the SH in turn mainly consists of huge oceans surrounding a comparatively much smaller continent at the austral pole;

    and that

    – (2) while the land/ocean ratio in the NH is 1:1.5, it is in the SH 1:4.

    That alone would be enough to explain the differences between SSTs in NH resp. SH: the bigger the ocean, the cooler it is!

    *
    Coming back to your tiny HadSST3 comparison window, I think in fact it would not be bad to expand it, and in addition to show the AMO near the two SST series:

    http://www.woodfortrees.org/graph/hadsst3nh/from:1880/mean:60/plot/hadsst3sh/from:1880/mean:60/plot/esrl-amo/from:1880/mean:60

    Here, due to the longer period, one better reduces all time series to their 60 month running means; otherwise you can’t see the forest for the trees.

    *
    Now, what would a statistician coming along with his MATLAB toolbox say, when having a look at this graph? Would s/he really say AMO is the driver of the NH SST?

    Moreover, it is pretty good apparent that HadSST3 SH suddenly looks a lot more similar to HadSST3 NH, when you compare it over a 140 year period.

    And it becomes pretty good apparent as well that both SST time series actually are leaving AMO’s trajectory!

    *
    In fact, this WFT graph disturbs me a lot, because WFT’s engineer Paul Clark decided to use AMO’s detrended variant, where here we rather would need the undetrended one: simply because we do not look today at AMO’s cyclic behavior, but want to compare it with undetrended time series.

    But… no: I won’t spend my time today evening in creating a graph comparing HadSST3 NH/SH with the correct AMO variant. No, no and no.

  9. NMK says:

    Thanks for great article

  10. Mike Moritz says:

    Good article ,but, I have a question for you. What is the effect of removing the nitric and sulfurous compounds from the fossil fuels wwe consume such as so2 from coal stack gases h2s from natural gas and from the petroleum refining sector?

  11. c1ue says:

    Very interesting data result.
    No El Nio shenanigans notwithstanding, it is certainly important to understand if the modern satellite record was distorted by non-cyclical or predictable events like volcanic cooling.
    Yet another example of how inherent bias could have expressed itself in the tuning or the various climate models

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  22. Stephen Lambros says:

    Greetings Dr Spencer. Very interesting chart regarding ocean temperature and the effects of El Chichon and Pinatubo. Your global lower atmosphere temperature record also shows a significant decrease in temperatures at the time of these volcanos. It would be most interesting to see the lower atmosphere temperature graph with the effects of these volcanos removed. The rate of temp increase in your atmospheric data would also be attenuated a fair bit over the last 42 years if it hadn’t been for these volcanos early in this period, would it not?

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