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.