Sawyer: prophetic or wot?

Two sources point me towards a Neville Nicholls letter about a 35 year old paper by Sawyer, but Inel gets the hat tip. Nicholls uses the paper to demonstrate that concern about GW is nothing new (it also blows the “everyone was predicting a new ice age in the 70’s” away, but thats another story), and he considers Sawyers about-right prediction of 0.6 oC T rise by 2000 as “perhaps the most remarkable long-range forecast ever made”. I suspect it doesn’t have much competition (any proposals?) but how does the Sawyer paper actually read?

Curiously enough, I had cause to be flipping through 70’s editions of Nature a month or so back, and came across Sawyer, and thought nothing much of it. Just shows you need fine judgement to get a letter into Nature 🙂

Having another look, in the light of Nevilles enthusiasm:

The paper is quite tentative. A leading box, presumably inserted by a subbie, says “…it is being realised that human activities are approaching a scale at which they cannot be completely ignored…”; and Sawyer says something similar in the article. Sawyers 0.6 oC comes from 2.4oC at 2*CO2 (from Manabe and Wetherald, 1968) combined with a 25% increase over pre-industrial by 2000 (from Inadvertent Climate Modification, MIT, 1971). The M+W figure is for equilibrium, and Sawyer later notes that the oceans would impose a lag on his values, so the 0.6 oC value should be reduced by an unspecified amount if it was intended as a prediction. But clearly it wasn’t: it was an illustrative example of the kind of change that might be expected.

We also have “a change of 0.6 oC by the end of the century will not be easy to distinguish from natural fluctuations” which was probably wrong: its not trivial; and the attribution work is definitely hard, but just seeing the change turns out to be fairly easy.

There is more equivocation over whether 2*CO2 would produce anything to worry about.

The conclusion was that there was no present cause for alarm but a need for further study. In the light of 35 more years, that was the correct thing to say then.

[Update: thanks to RH, you can now read it for yourself.

5 thoughts on “Sawyer: prophetic or wot?”

  1. I saw this paper mentioned in correspondence to Nature this week, couldn’t access the original paper though.

    The (prediction / projection) for CO2 in 2000 is not bad, 350ppm as opposed to 370ppm (measured) from a pre-industrial level of 280ppm.


  2. ” … we didn’t change the Earth’s weather, but its climate. There’d be no point in trying to explain the difference to you, I guess. They stepped up the CO2 content of the atmosphere, producing an increased blanketing effect. At first the equatorial regions were uncomfortably hot as a result; but when the thing stabilized again a lot of the polar caps had melted, and a lot of formerly desert land in the torrid zones, which had been canalized for the purpose, had flooded in consequence. The net result was an increased evaporation surface and, through a lot of steps a little too technical for the present discussion, a shallower temperature drop toward the poles….”

    Hal Clement, “Cold Front”
    First published in _Astounding_ July 1946


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