35-year anniversary of Sawyer’s remarkable paper on “Man-made CO2 and the ‘greenhouse’ effect”

August 30, 2007 at 12:56 pm | Posted in 1972, 2007, Accurate, AR4, Carbon dioxide, Climate change, Climate science, CO2, Greenhouse effect, History, IPCC, Met Office, Nature, Nicholls, Sawyer, UK | 11 Comments

A warning we ignored 35 years ago

Neville Nicholls
August 31, 2007

MANY people think that our concern about carbon dioxide and global warming is a modern preoccupation driven by the attention of high-profile personalities, politicians and green activists. But Al Gore did not discover global warming. Nor did Tim Flannery, Peter Garrett, Greenpeace or Malcolm Turnbull. Scientific concern about global warming is not new.

A single scientific paper, published more than three decades ago, 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.

After summarising recent calculations of the likely impact of increasing carbon dioxide concentrations on global surface temperature, 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”.

Examination of the global surface temperature over the latter part of the 20th century shows that in fact the temperature rose about 0.5 degrees between the early 1970s and 2000. Considering that global temperatures had, if anything, been falling in the decades leading up to the early 1970s, Sawyer’s accurate prediction of the reversal of this trend, 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. The IPCC assessment involves more than 400 authors, about 2500 reviewers, and runs to several thousand pages with many thousands of references. Such a comparison shows that much has been done to address the concerns and uncertainties expressed by Sawyer at the time.

He was concerned that the rudimentary understanding of cloud processes and other climate system feedback resulted in uncertainties regarding predictions of warming. At the time, climate models were in their infancy, but Sawyer saw them as the best way to examine this feedback and reduce the uncertainties in climate change predictions. Since then, models have improved substantially and now include many more processes in more detail than was possible in the early 1970s, and the various climate processes that may enhance or offset the effects of carbon dioxide have been studied in detail.

Despite these advances, our best estimate of the warming to be expected from a doubling of atmospheric carbon dioxide concentration has changed little from Sawyer’s time. 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 scientific consensus of Sawyer’s time was very similar to the scientific consensus in 2007.

Of course, better climate models and improved data and analyses have allowed the IPCC to discuss and even project possible changes in many other meteorological variables than could Sawyer, including extreme weather of various kinds as well as sea-level. The IPCC now also looks in detail at regional aspects of climate change — a subject not even considered by Sawyer. Perhaps the greatest difference, however, is the emphasis on the impacts of climate change.

While the IPCC assessment devotes a volume to this subject, Sawyer could only conclude, after conceding that climate variations of only a fraction of a degree can have “considerable economic importance” that “although there may be no immediate cause for alarm about the consequences of carbon dioxide in the atmosphere, there is certainly need for further study”.

Perusal of the IPCC volume devoted to the impacts of climate change on natural and human systems leaves one feeling far less sanguine than Sawyer was 35 years ago.

The anniversary of Sawyer’s paper reminds us that 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.

Despite claims to the contrary, 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. Other scientific papers around that time also drew attention to the warming expected from the anthropogenic increases in greenhouse gas emissions.

Neville Nicholls is in the school of geography and environmental science at Monash University and is a lead author for the IPCC AR4.

I was pleased to find this online in full, as I think it is the same article that appears in today’s Nature, but is behind a paywall.



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  1. Really interesting! It’s nice to see things about climate change that are NOT about Al Gore, since nay-sayers seem to like to attack him and his film instead of the actual issues at hand. Thanks for sharing.

  2. This is not exactly the letter that appears in Nature, but the gist of it is the same.

  3. It makes me sad to read things like this. Coincidentally, my post is similar, in a way. These people struggled so hard studying and learning about these problems, and tried to bring it to our attention, and decades later, we’ve let things continue to worsen.

    It’s upsetting to read these when you know that their efforts ended up being basically futile.

  4. Not futile. I remember reading this. It changed my idea of what needed attention, on my watch.

  5. Hello Darmok and Hank,

    Thanks for your comments. Futile, or not futile?

    Whether or not the scientists’ efforts thirty-plus years ago were futile depends on what you choose to measure success with.

    If success is measured by the action taken by people worldwide to combat global warming, then the efforts of the scientists years ago were futile, but only because of the lack of effort by the rest of us!

    If success is measured by the action taken by scientists worldwide to study climate change as a matter of priority, so that the focus, quantity and quality of research, and the development of climate models, were improved significantly, then the efforts of the scientists were certainly not futile—they were most valuable.

    It seems to me that scientists have done an excellent job providing a continuing comprehensive and detailed understanding of climate change, and there is plenty of information available now with which to make informed decisions. We need to highlight (for others)—and then ignore—the misinformation campaign from those who care not a jot about the natural world as long as they can plunder it.

    It is way past action-time for the rest of us to rise to the challenge and make a significant difference to the health of our climate system and all the intertwined ecosystems that depend upon it.

  6. Ah, yes, I didn’t mean to be quite so negative. I was already in a foul mood because of the baijis and people’s attitudes in general and then you read about all the work these people did and how full of optimism they were and you see what the results ended up, regardless.

    In any case, no, I don’t ultimately believe this struggle is futile—if I did, I wouldn’t keep writing about it! But it’s just frustrating that scientists discover these things and warn us and yet nothing happens.

  7. I agree, Darmok (and I don’t think you were being overly negative). Unfortunately, the baijis (river dolphins) are one example of many animals and plants we will have the displeasure of realising will tend to extinction during our lifetime, especially if we carry on with emissions as usual.

  8. While this is interesting, Mr. Nicholls is playing fast and loose with the figures. Sawyer said 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

    In fact, the HadCRUT3 global temperature dataset shows that the world warmed 0.4° from 1972-2000, not 0.5° as Sawyer says. And the Mauna Loa dataset shows that the CO2 increased by only 13% during that time, not 25%.

    More to the point, using the actual increase in CO2, and the climate sensitivity used by Sawyer (0.5°/W-m2, or 1.9°/doubling of CO2), we should only have seen a 0.3° warming during the period.

    Sawyer’s numbers, while interesting, were nowhere near as accurate as the letter to Nature claims.


  9. The best estimate of the future climate is still the current climate, and even the most extreme AR4 model estimates result in a year 2100 climate type distribution not very different from the current climate.

    Calling Sawyer’s estimates “accurate” is not as justified as calling them coincidentally close to the actual result. Any stronger conclusion argues against the necessity of complex coupled ocean atmosphere general circulation models, which represent myriad positive and negative feedbacks as well as the thermal inertia of the oceans.

  10. […] 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 […]

  11. My conversation with inel on this subject continues here.

    My best to everyone,


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