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The 1975 US National Academy of Sciences/National Research Council Report


Review by W M Connolley

This little-read report appears to serve as a useful summary of the state of opinion at the time (aside: I was prompted to read this by someone who thought the report supported the ice-age-was-predicted threoy [1]: as all too often happens, the report when actually read does no such thing...), which opinion was (my summary) "we can't predict climate yet, we need more research".

I know of only two places where this report is referred to in "current" debate (you know others? good: mail me: the page from the Cato Institute (discussed on the main page, the main quote from which is "There was even a report by the National Research Council of the U.S. National Academy of Sciences reaching its usual ambiguous conclusions"), and in a page from sepp [remember, children, a link from this page does not imply endorsement of the contents...], an excerpt from which is below:

From issues/glwarm/sciaddheat.html:

But this exaggerated concern about global warming contrasts sharply with an earlier NAS/NRC report, "Understanding Climate Change: A Program for Action." There, in 1975, the NAS "experts" exhibited the same hysterical fearsó-this time, however, asserting a "finite possibility that a serious worldwide cooling could befall the Earth within the next 100 years."

The 1975 NAS panel claimed to have good reason for their fears: Global temperatures had been in steady decline since the 1940s. They considered the preceding period of warming, between 1860 and 1940, as "unusual," following as it did the "Little Ice Age," which had lasted from 1430 to 1850.

This is a gross misrepresentation of the 1975 NAS report; the Cato summary is more accurate.

But anyway, what about the report itself...?

Ah yes, I'm glad you asked. OK, the SEPP stuff about hysterical fears is nonsense, the report is a calm, mannered assessment of the science.

Let's write its ISBN, so you can find it: 0-309-02323-8.

From the foreword (by V E Suomi, Chair of the US Committee for GARP):

"...we do not have a good quantitative understanding of our climate machine and what determines its course. Without the fundamental understanding, it does not seem possible to predict climate...".

I believe that this is an accurate assessment of the state of knowledge at the time.

From the preface (by W L Gates and Y Mintz):

"Our response to the concerns [about climate variations [WMC]] is the proposal of a major new program of reseach designed to increase our understanding of climatic change and to lay the foundation for its prediction".

So far so good: the report doesn't believe prediction can yet be done, and its response is to recommend more research, not to make predictions.

From the start of the Introduction:

"Climatic change has been a subject of intellectual interest for many years. However, there are now more compelling reasons for its study: the growing awareness that our economic and social stability is profoundly influenced by climate and that man's activities themselves may be capable of influencing the climate in possibly undesirable ways. The climates of the earth have always been changing, and they will doubtless continue to do so in the future. How large these future changes will be, and where and how rapidly they will occur, we do not know".

Again: at the time, they believed (correctly) that prediction (then) was not possible. It is clear that the report does not intend to make recommendations about actions to be taken in the face of climate change: its emphasis is on recommending increased research (in fact the reports recommendations are quite unambiguous in this regard: so the Cato Institutes summary is wrong too. Hey ho).

A summary of chapter 2, "Summary of principal conclusions and recommendations":

  1. Establish National climatic research program
  2. Establish Climatic data analysis program, and new facilities, and studies of impact of climate on man
  3. Develope Climatic index monitoring program
  4. Establish Climatic modelling and applications program, and exploration of possible future climates using coupled GCMs
  5. Adoption and development of International climatic research program
  6. Development of International Palaeoclimatic data network
  7. Learn how to spell "programme"
Ha ha, only joking on that last one folks... so, once again: research needed.

From chapter 3, "Physical basis of climate and climatic change", section "Simulation and predictability of climatic variation", subsection "Climate modeling problem":

"The attack on this problem is in its infancy. ... Efforts to assemble such models [Coupled GCMs [WMC]] are just getting under way...".

From chapter 4, "Past climatic variations - projections of future climates", section "Inference of future climates from past behaviour", subsection "mans impact on climate",

"...the rapidity with which human impacts continue to grow in the future, and increasingly to disturb the natural course of events, is a matter if concern."

Then follows a section saying that CO2 is currently more influential (probably) than aerosols but this may change; then a section on "thermal pollution, clouds, and surface changes", which ends:

"Again, however, it is only through the use of adequately calibrated numerical models that we can hope to acquire the information necessary for a quantitave assessment of the cliatic impacts."

OK, OK! I'm convinced: they didn't predict disaster. But what about the "finite possibility that a serious worldwide cooling could befall the Earth within the next 100 years" ?

Cut to Appendix A, "Survey of Past Climates". Go right to the end: "Likelihood of a major deterioration of the global climate in the years ahead", and a discussion of the possibility of th next ice age:

"there seems little doubt that the present period of unusual warmth will eventually give way to a time of colder climate, but there is no consensus as to the magnitude or rapidity of the transition. The onset of this climatic decline [nb: colder temperatures is automatically a decline? any change is a decline? WMC] could be several thousand years in the future, although there is a finite probability that a serious worldwide cooling could befall the earth within the next 100 years".

So: this is hysterical fears? Well, judge for yourself. Notice, incidentally, that SEPP have misquoted the report in minor ways: they replace "probability" with possibility, and add capitalisation to "earth". [Hey, I typed all this stuff in by hand and its dull: I get to be picky about other peoples errors].

The notion of a "finite probability" is literally vacuous, since probabilities are by definition between 0 and 1, and are thus always finite. They mean, the idea of "not infinitesimal" or "not very very tiny" I suppose: but in practice what non-tiny value they mean cannot be inferred from the above, which goes back to being about meaningless.

However, lower down they add: "The question remains unresolved. If the end of the interglacial is episodic in character, we are moving toward a rather sudden climatic change of unknown timing, although as each 100 years passes, we have perhaps a 5% greater chance of encountering its onset If, on the other hand, these changes are more sinusiondal in character, then the climate should decline gradually over a period of thousands of years. [this assumption that the interglacial can only last 10-ish kyr may have been correct from the info of the time; it is now dubious or wrong: WMC].... These climatic projections, however, could be replaced by quite different future climatic scenarios due to man's inadvertent interference with the otherwise natural variation...

and then goes on to discuss CO2 and aerosols.

So, we're back were we began: prediction is impossible: CO2, aeosols, glacial cycles are competing influences amongst others but we don't know which will occur. Which was, then, the correct assessment.

Questions and Comments

Here is a question that was asked:
> How different are things today, really?
> Wouldn't it be fair to say that the NAS is saying something
> basically similar now? Couldn't they fairly argue that there
> is a "finite probability that a serious worldwide WARMING
> could befall the Earth within the next 100 years" and also
> be "guilty" of the same wishy-washy weaseling that took
> place in 1975? 
My reply is:

Good question. Take the IPCC 2001 "summary for policymakers" report (ie, at the front, not buried in an appendix): section heading "global average temperature and sea level are projected to rise under all ipcc sres scenarios", subsection "temperature", first point: "the globally averaged sfc temp is projected to increase by 1.4 to 5.8 oC over the period 1990 to 2100..." Later "This approach suggeests that anthro warming is likely(7) to lie in the range 0.1 to 0.2 oC per decade over the next few decades under the is92a scenario..." where (7) is the footnote: the following words are used: "...likely (66-90% chance);...".

So, they deliberately avoid the problem of essentially meaningless "finite probability" stuff and quantify their probabilities. Also the temperature projections are given clear numbers. And so on.


[1] This miss-spelling shall remain in perpetuity in "honour" of the unknown skeptic.

By WMC June 2001 and subsequently.