Celebrating Sawyer’s 35th anniversary in Nature

October 2, 2007 at 1:46 pm | Posted in Climate science, CO2, IPCC, Met Office, Nicholls, Sawyer, Temperatures | 6 Comments

Dear Willis Eschenbach,

Welcome to our party! For others who are just joining us, I should explain that in my earlier post, we were celebrating the 35-year anniversary of:

“a single scientific paper, published more than three decades ago, [that] can place the discussions about climate change into historical perspective. Tomorrow it will be 35 years since the leading science journal Nature published a review paper entitled “Man-made carbon dioxide and the ‘greenhouse’ effect“, by the eminent atmospheric scientist J. S. Sawyer, director of research at the United Kingdom Meteorological Office.

In four pages, Sawyer summarised what was known about the role of carbon dioxide in enhancing the natural greenhouse effect leading to warming at the earth’s surface, and made a remarkable 28-year prediction of the warming expected to the end of the 20th century. His prediction can now be compared with what has been observed. We can also compare his review of the science in the early 1970s with that in the latest (2007) assessment from the Intergovernmental Panel on Climate Change.”

I appreciate your comment, and I can understand what you are getting at. However, with all due respect, you have chosen to nitpick one aspect of the article referenced, without appreciating (or while deliberately ignoring?) the whole picture presented in the article and the paper which it describes.

I have not read the letter that appeared in Nature, though I do know the author is also Neville Nicholls, and I am informed the gist of the article I found is the same as the letter accessible to Nature subscribers here:

Climate: Sawyer predicted rate of warming in 1972

Neville Nicholls

 

CONTEXT: …carbon dioxide and the “greenhouse” effect’ by the eminent atmospheric scientist J. S. Sawyer (Nature 239, 23–26; 1972). In four pages Sawyer summarized what was known about the role of carbon dioxide in enhancing the natural…

Nature 448, 992 – 992 (29 Aug 2007) Correspondence

  • “Scientific concern about global warming is not new.”
  • We “can place the discussions about climate change into historical perspective.”
  • “Sawyer … made a remarkable 28-year prediction of the warming expected to the end of the 20th century.”
  • “Sawyer concluded that the ‘increase of 25 per cent in carbon dioxide expected by the end of the century therefore corresponds to an increase of 0.6 degrees in world temperature — an amount somewhat greater than the climatic variations of recent centuries’. “
  • “Sawyer’s accurate prediction of the reversal of [the mean global surface temperature] trend [that was evident at the time of his assessment], and of the magnitude of the subsequent warming, is perhaps the most remarkable long-range forecast ever made.”
  • Sawyer’s succinct summary of the climate change science understood at that time can be compared with the four volumes of the IPCC Fourth Assessment on Climate Change being released through 2007.”
  • “Our best estimate of the temperature increase that would result from a 25 per cent increase in atmospheric carbon dioxide concentrations is still around 0.6 degrees.”
  • “the understanding of the effects of carbon dioxide on the global climate was sufficiently advanced 35 years ago to allow an accurate 28-year prediction of warming.”
  • “our understanding of the greenhouse effect and global warming is not reliant on modern climate models and nor is it a modern preoccupation.”
  • Nor is it correct to claim that in the 1970s climate scientists were predicting global cooling — Sawyer’s paper accurately predicted exactly the opposite, based on the best science available.”

I can see why you have chosen to pick on accuracy for your dismissal of this piece. It is easy. All you have to say is that Sawyer’s actual numerical prediction for that period (1972-2000) was not exactly borne out by precise measurements, and you think you’ve made your case and won that particular part of your overall argument. As it stands, “fast and loose with the figures” would be a more appropriate description of your own response to Neville Nicholls’ letter and article, than his originals. (I am deliberately not repeating your own numbers, as you chose one comparison that suited your purposes and apparently had a typo in one number/author reference you mentioned.)

I acknowledge that the CO2 concentrations did not rise in that 28-year period as predicted. Yes, they rose about 13%, rather than 25%.

I agree that this lower radiative forcing from CO2 would correspond to a smaller rise in mean global surface temperature. However, CO2 alone, though important, is not the only source of forcing. There are other components that play a part in changing mean global surface temperatures (in the observed figures, and always).

If you look back at the article to which I was referring, Nicholls’ use of the word “accurate(ly)” occurs three times:

  • accurate reversal of the trend (which was flat, or showed temperatures declining slightly)
  • accurate magnitude of the warming associated with an increase in carbon dioxide concentrations, i.e. CO2 x 1.25 => temp+0.6°C
  • accurately predicted the opposite of cooling

All three instances make sense and are valid, despite your quibbling over precise particular numbers.

A 25% increase in CO2 concentrations still—after thirty-five years’ worth of expert research and more and more powerful computers upon which increasingly sophisticated model runs take place—corresponds to an increase of around 0.6°C in global surface temperatures. On that prediction, Sawyer was pretty accurate, I’d say.

You are trying to trip others up on an easy point, which is that the CO2 concentrations did not rise as much as expected in Sawyer’s day when he made his 28-year prediction. We can only be thankful for that. Party on!

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6 Comments »

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  1. Inel, thank you for your comments. The point that I made is not a minor one as you seem to think. Sawyer said that if CO2 rose 25%, the temperature would rise by 0.6°. The temperature did rise about that much … but the CO2 only rose half that much.

    Sawyer got the right answer, but only because he overestimated the CO2 rise by a fact of two. In other words, his method was out by 100% … hardly an accurate prediction.

    Yes, he did predict that temperatures would rise. But given that they have been rising for the last 300 years, this can hardly be thought of as as a groundbreaking claim. There had already been two major “the world is heating up, we’re all going to fry” scares, one in the 1890s and one in the 1930s. So the idea that the globe was warming was scarcely novel.

    And since it was a certainty that the world would either heat or cool, he had a 50% chance of being right … not exactly daunting odds. Success on a 50/50 bet is hardly worth noticing, much less celebrating as “accurate”. If I flip a coin and call “heads”, would you call my prediction “accurate”, and write about it thirty years later? “Wow, a guy called heads, and you won’t believe it, but it actually came up heads. Man, how accurate is that guy? Amazing!” …

    You say:

    A 25% increase in CO2 concentrations still—after thirty-five years’ worth of expert research and more and more powerful computers upon which increasingly sophisticated model runs take place—corresponds to an increase of around 0.6°C in global surface temperatures. On that prediction, Sawyer was pretty accurate, I’d say.

    No. Sawyer was lucky. He overestimated the amount of CO2, and overestimated the climate sensitivity. These, by chance, cancelled out. You can call that “accurate” if you wish … but if I did that in my job as an accountant, I’d be fired. No one would congratulate me, no one would say “gosh, that’s pretty accurate!” They’d fire me, and rightly so.

    Here’s another way to look at it. If Sawyer had been correct about the future CO2 rise, if he had estimated it to rise by 13%, he would have said the temperature would rise by 0.3° … would you still have been saying that his was a very accurate prediction?

    Of course not, he would have been way off. Surely you must recognize the irony that if he had been right about the CO2 … he would have been wrong about the temperature. This is because his estimate of the climate sensitivity was very different from the commonly accepted modern value.

    So no, there’s nothing particularly “accurate” about Sawyer’s work. Interesting, yes. Ahead of its time, yes. But accurate?

    No.

    w.

  2. A 25% increase in CO2 concentrations still—after thirty-five years’ worth of expert research and more and more powerful computers upon which increasingly sophisticated model runs take place—corresponds to an increase of around 0.6°C in global surface temperatures. On that prediction, Sawyer was pretty accurate, I’d say.

    The contents of Sawyer’s 4-page paper cannot be dismissed as “lucky”.
    .
    Willis, you seem to think that I am arguing the accuracy of Sawyer’s 28-year prediction in absolute black and white terms, as though CO2 alone were solely responsible for the entire mean global surface temperature anomaly between 1972 and 2000. I am not. It is not.
    .
    In fact, my focus is not even on that 28-year period, but rather on the fact that this paper is noteworthy and we should celebrate its anniversary. Recognition of what was known 35 years ago provides people new to the topic some historical context for the development of our understanding of climate change.
    .
    You, on the other hand, are the one who is arguing accuracy, or lack thereof.
    .
    If you want to play numbers, consider this. You wrote earlier:

    In fact, the HadCRUT3 global temperature dataset shows that the world warmed 0.4° from 1972-2000, not 0.5° as Sawyer says.

    By the way, it is Nicholls who says 0.5°C, not Sawyer. Sawyer isn’t doing the comparison with his own prediction 35 years later: Nicholls is.
    .
    Now you add:

    Sawyer said that if CO2 rose 25%, the temperature would rise by 0.6°. The temperature did rise about that much … but the CO2 only rose half that much.

    You chose to quote HadCRUT3 data, i.e. 0.4°C, and are now telling me that 0.6°C is a “rise about that much”, which is a 50% increase on 0.4°C and a significant margin of error that an accountant should get into trouble over.
    .
    On the other hand, there are situations in which we could agree to acknowledge this predicted rise in mean global surface temperatures has the same sign and is of the same order of magnitude as that observed, and leave it at that. Context is key.

  3. inel, thanks for your comment. You say:

    On the other hand, there are situations in which we could agree to acknowledge this predicted rise in mean global surface temperatures has the same sign and is of the same order of magnitude as that observed, and leave it at that. Context is key.

    That we can agree on. And you are right, I mis-spoke calling Nicholls “Sawyer”.

    On the other hand, the global temperature rose about 0.5°C during the 1700’s, the 1800’s, and the early part of the 1900’s, so getting the sign and order of magnitude correct for the latter part of the 1900s is not all that difficult.

    Also, Sawyer did not predict the turn in the trend (from cooling to warming) as Nicholls claimed. Looking at trailing 28 year trends, they bottomed out in 1965, and by 1971 it had been a warming trend for three years. Sawyer merely predicted a continuation of the existing warming 28 year trend. If he had predicted warming in 1960, when the trends were cooling, it would have been more impressive.

    However, the paper is indeed noteworthy, as Sawyer was one of the first people to make this claim.

    w.

  4. Dear Willis,

    I am glad we can agree on some general points, though it is a pity you are seeking to undermine Sawyer’s achievements by retrospective nebulous pettifogging 😉

    Er, which claim, may I ask, do you think Sawyer is one of the first to make?

    In spite of the enormous mass of the atmosphere and the very large energies involved in the weather systems which produce our climate, it is being realized that human activities are approaching a scale at which they cannot be completely ignored as possible contributors to climate and climatic change.

    Is it this one?

  5. No, I was speaking of the claim that we could accurately predict future temperatures using CO2 levels.

    To date the claim has not been shown to be correct, but he was the first to make it.

    What were “Sawyer’s achievements” that I was seeking to undermine? When he made the claim (1972), temperatures had been rising for 22 years (HadCRUT3 data), so predicting continued warming was not an achievement. His estimate of the future evolution of CO2 levels was off by a factor of two, and his estimate of climate sensitivity was about half of the modern estimate. He was lucky, his two errors offset each other … but that’s hardly an achievement.

    So, what were his achievements?

    w.

  6. PS — I must admit, however, that I was impressed by the accusation of “retrospective nebulous pettifogging” … didn’t know I was capable of such an intellectual achievement.

    All the best,

    w.


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