The IPCC AR4 Models Of 20th Century Surface Temperatures With And Without Anthropogenic Forcings

This is a quick post. It reinforces one of the points made repeatedly in recent comparisons of the observed rise in Global Surface Temperatures during the 20thCentury and of those hindcast by the Multi-Model Mean of the models used by the IPCC in AR4. And I also want to be able to reference one of the following graphs (Figure 3) in an upcoming summary of the recent AR4 model versus observations posts. (I have at least one more post on these comparisons before the summary.)

For the post The IPCC Says… – The Video – Part 1 (A Discussion About Attribution), I replicated the data that represented the Multi-Model Mean hindcast of Global Surface Temperature anomalies presented by the IPCC in Figure 9.5 of AR4. And in that post, it was cell a of Figure 9.5, which represented the models forced with natural and anthropogenic forcings. The post It Really Should Go Without Saying, BUT…presented the replicated Multi-Model Mean of the models forced by only natural (solar and volcanic aerosols) forcings. For both, I created the replica data using the X-Y coordinates of Microsoft Paint. So consider that when viewing the following. The other point to consider is that not all of the modelers presented the hindcast for natural forcings only, so there are differences in the numbers of models presented by the IPCC in the two datasets.

Figure 1 presents the replica of the Multi-Model Mean of the 20th Century Global Surface Temperature hindcasts presented by the IPCC in Figure 9.5 of AR4. It includes the data from cell a, which included natural and anthropogenic forcings, and the data from cell b, which showed the hindcast for natural (solar and volcanic aerosols) forcings only. The greatest divergence occurs during the late 20thCentury.

Figure 1

If we subtract the mean of the hindcasts with natural forcings only from the hindcasts that used natural and anthropogenic forcings, Figure 2, we’re left with what should be a rough approximation of the anthropogenic component of the models.

Figure 2

The hindcast difference (anthropogenic and natural forced minus natural forced) is again illustrated in Figure 3, but in Figure 3 the two warming periods of 1917-1944 and 1976-2000 are also shown, as are the trends for those two periods. The linear trend of the anthropogenic component during the late warming period of 1976-2000 is more than 8 times higher than the trend of the early warming period.

Figure 3

One would think that, if anthropogenic forcings were the dominant cause of the rise in surface temperatures during the late warming period, the observed rate at which surface temperatures rose during the late warming period would be much higher than the rate during the early warming period. But it’s not, as shown in Figure 4.

Figure 4

(Keep in mind: we’ve already established in the earlier posts that the observed early warming period cannot be simulated by the models that also include natural forcings.)


About Bob Tisdale

Research interest: the long-term aftereffects of El Niño and La Nina events on global sea surface temperature and ocean heat content. Author of the ebook Who Turned on the Heat? and regular contributor at WattsUpWithThat.
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10 Responses to The IPCC AR4 Models Of 20th Century Surface Temperatures With And Without Anthropogenic Forcings

  1. When are pollutants as H2O, CO2 in the upper atmosphere > upper atmosphere is warmer – on the ground milder. Therefore upper atmosphere and the ground temperatures are in harmony; therefore taking one in consideration but not the other; is same as taking one hemisphere but not the other. They all use my ”children’s see-saw plank theory” the more one goes up – the more the other goes down, but overall, same temperature every hour of every day, year and century. The extra heat accumulated for the last 150 years; if you collect all of it; you wouldn’t have enough to boil one chicken egg. Because extra heat is not accumulative. Thanks to oxygen + nitrogen expending when get warmer – shrinking when get colder

    In my backyard / on the ground, I can identify 10-15 different temperatures; not one IPCC’s thermometer to monitor – in how many other backyards they don’t monitor? How about on every 3km3 2m above the seawater – those temperatures change constantly… are they on the same globe they are talking about?

  2. Joe's World says:


    The drawback to consensus science is that if one scientist is incorrect, then ALL are incorrect.
    Yet these scientists keep pushing to cover for each other due to the nature of the beast of consensus.

  3. Pascvaks says:

    You’re a “Teacher” in the finest sence of the term. You’ve opened more doors and windows for me than I can count. Thank you good Doctor! Thank you for taking the time and making this great effort of all of us.

    Now I can even see the spacing of the “solar cycle” periods in the Fig. 4 graph where before I could not.

    PS: Merry Christmas! God Bless and Keep You! (an old Irish saying, ya’know;-)

  4. Bob Tisdale says:

    Pascvaks: And happy holidays to you!!!!!!!

    PS: Sure wish I could see those solar cycles.

  5. Pascvaks says:

    Bob –
    Hi’s and Lo’s? (only looking at the ~11 yr hi and lo points) haven’t checked for how close these come to the actual sunspot cycle, or what lag is in place, but there’s a definite(?) series that seem to correspond. Hadn’t noticed it before in your graphs, this time it seemed to bite me on the nose. I may be out to lunch;-)

  6. Pascvaks says:

    Ref – Your Figure 4 – (1976-1985)
    Ref @ –
    Solar Cycle 21 (1976/06-1986/06)

  7. Frank says:

    Bob wrote: “Keep in mind: we’ve already established in the earlier posts that the observed early warming period cannot be simulated by the models that also include natural forcings.” Could you provide links to these posts? Unfortunately, for me, Figure 3 above proves exactly the opposite – natural forcings account for almost all of the 1920-1940 warming. The IPCC doesn’t like to publicize the that such a large rapid warming could be mostly due to natural factors – at least according to their dubious models and attribution methods – but I stumbled across this reference in AR4.

    Nozawa et al GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L20719, 4 PP., 2005
    Detecting natural influence on surface air temperature change in the early twentieth century

    We analyze surface air temperature datasets simulated by a coupled climate model forced with different external forcings, to diagnose the relative importance of these forcings to the observed warming in the early 20th century. The geographical distribution of linear temperature trends in the simulations forced only by natural contributions (volcanic eruptions and solar variability) shows better agreement with observed trends than that does the simulations forced only by well-mixed greenhouse gases. Using an optimal fingerprinting technique we robustly detect a significant natural contribution to the early 20th century warming. In addition, the amplitude of our simulated natural signal is consistent with the observations. Over the same period, however, we could not detect a greenhouse gas signal in the observed surface temperature in the presence of the external natural forcings. Hence our analysis suggests that external natural factors caused more warming in the early 20th century than anthropogenic factors.

  8. Bob Tisdale says:

    Frank says: “Could you provide links to these posts?”

    Yup. For natural forcings only, see here:

    And for the Natural+Anthopogenic forcings see here:
    And here:

    You added, “Unfortunately, for me, Figure 3 above proves exactly the opposite – natural forcings account for almost all of the 1920-1940 warming.”

    Natural forcings may account for most of the warming in the models but even with the addition of anthropogenic forcings, the models cannot come close to matching the observed warming.

    Frank: Do you have a copy of Nozawa et al 2005? There’s a paywall on the only version I can find. And it’s not worth $25 to me. I’m only interested in knowing which of the outdated TSI datasets they used.

  9. Frank says:

    Bob: I’ve only read the abstract of Nozawa and seen the data they included in one of the key attribution figures (9.5?) used in Chapter 9 of AR4. I was startled to see the clear attribution of warming in the first half of the 20th century to natural factors in Nozawa – not mentioned by the IPCC, of course – explaining why the attribution statement is limited to the second half.

  10. Bob Tisdale says:

    Frank: The IPCC actually does attribute the early warming period to natural forcings. I discussed it in the following post under the heading of ON THE IPCC’S CONSENSUS (OR LACK THEREOF) ABOUT WHAT CAUSED THE EARLY 20th CENTURY WARMING:


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