Global Cooling Myth in the 70’s

Many claim that in the 1970’s all scientists believed the earth was cooling. Factual examination of the controversial report reveals that there was a consensus. The consensus was we don’t know enough yet. The confirmation of the Milankovitch cycles indicated that we were to begin a cooling phase, the introduction of industrial greenhouse gases indicated we could interrupt the natural cycle. More study was needed.

NASA GISS Global Land-Ocean Temperature Index
Global Land-Ocean Temperature Index 2008

As in all things science and reason, context is required to understand relevance of any data or scope of understanding. In the case of the global cooling myth, let’s take a look at the context.

This is around the time that the “Milankovitch Cycles’ were confirmed by the deep ocean sediment core studies, thus solidifying the understanding that the earths climate system is subject to long term natural cycle influences that significantly alter our climate.

Ice age predicted in the 70’s? As we show below, not really. We came out of the last ice age 15,000 years ago. Typically we would go back into an ice age as that is the natural cycle. The industrial imposed climate forcing is so large that we can not at this level of forcing, return to an ice age.


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

UNDERSTANDING CLIMATIC CHANGE: A program for action (ISBN: 0-309-02323-8)

Review by W M Connolley (additional context and material provided by J P Reisman)

A careful review of the report shows no consensus on global cooling. In fact quite the opposite is expressed by the generally views of the report. There was no consensus, or anything that could remotely be called a consensus, of ‘ALL’ scientists as has been claimed by global warming denialists.” W M Connolley

W M Connolley summary of report: “We can’t predict climate yet, we need more research”.

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…”.

In 1974, when this report was being put together the focus was understanding the natural climate variability as well as understanding potential human impacts. J P Reisman

“I believe that this is an accurate assessment of the state of knowledge at the time.” W M Connolley

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

“The increasing realization that man’s activities may be changing the climate, and mounting evidence that the earth’s climates have undergone a long series of complex natural changes in the past, have brought new interest and concern to the problem of climatic variation. The importance of the problem has also been underscored by new recognition of the continuing vulnerability of man’s economc and social structure to climatic variations. Our response to these concerns is the proposal of a major new program of research designed to increase our understanding of climatic change and to lay the foundation for its prediction”.

First Paragraph – Page ix

“The report doesn’t believe prediction can yet be done, and its response is to recommend more research, not to make predictions.” W M Connolley

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”.

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 modeling 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

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…”. W M Connolley

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.”

W M Connolley “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 quantitative assessment of the climatic impacts.”

What about the “finite possibility that a serious worldwide cooling could befall the Earth within the next 100 years” ?

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 the 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“.

There are no conclusions or consensus that the world is going back into and ice age.

W M Connolley: 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, aerosols, glacial cycles are competing influences amongst others but we don’t know which will occur. Which was, then, the correct assessment. W M Connolley

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