About That 1970s Global Cooling...

by Brian Dunning
October 6, 2015

Today, climate scientists tell us the Earth is warming. Some people deny that, and point out that in the 1970s, climate scientists said the Earth was cooling, perhaps headed into another ice age. Today's scientists counter that it wasn't climate scientists who said that, it was the media. The deniers counter that's just a dodge, that it was, in fact, the scientific consensus in the 1970s. If the scientific consensus then was so wrong, then how can a scientific consensus today be any more reliable? One side says "Nyah nyah nyah," and the other counters with "I know you are but what am I," only to be told "You and what army?" and are then shut down with a great big raspberry. Today we're going to slide on our corduroy bellbottoms and go back to the 1970s, to see who said the Earth was cooling, and how many real scientists agreed with it.

Today we hear certain groups stress that there was a lot of reporting in the 1970s that scientists felt an ice age was coming. This is quite true, there were a huge number of such news reports throughout that decade. It was a real presence in the popular media, and no amount of historical revisioning changes that. For a fair example of where this issue stood in the public consciousness, check out this episode of the popular TV show In Search Of with Leonard Nimoy, titled The Coming Ice Age, from 1978:

Climate experts believe the next ice age is on its way. According to recent evidence, it could come sooner than anyone had expected. At weather stations in the far north, temperatures have been dropping for thirty years. Sea coasts long free of summer ice are now blocked year round. According to some climatologists, within a lifetime, we might be living in the next ice age.

Websites of global warming deniers give long lists of newspaper and magazine articles from the 1970s (like this one and this one) trumpeting the alarm that an ice age is on its way. Any reasonable person who were to look at one of these pages would have to conclude that the science was pretty clear back then: the earth is cooling, and cooling fast. Forty years later, we can now see that it didn't happen. And so, the global warming deniers argue, if scientists were that wrong back then, why shouldn't we think they're wrong now when they say global warming is happening?

Allow me to summarize. It is true that all this news did appear in the popular mass media and TV shows like In Search Of, but believe it or not, the news media had the same proclivity then as they do now for reporting what's new and sensational. Climatologists had known for a long time about the greenhouse effect and the warming produced by carbon dioxide, but until the latter half of the 20th century, nobody had really been able to put together predictive models. Then in the late 1960s, the University of Washington published the cooling effects produced by sulfate aerosols in the atmosphere, which reflected solar radiation away from the Earth. This was a profound new twist, and suddenly everyone started testing for sulfate aerosols, an industrial pollutant which is also the cause of acid rain. You may remember that from the 1970s as well. Cooling effects were added onto climate models, and for a time, a number of climatologists weren't sure which effect was going to be the more significant. That was all it took to make a sensational headline, and the mass media ensured that we've have shocking fears to keep us alarmed throughout the decade. But beneath the surface, the response of mainstream climatologists was more measured.

For the uncertainty that did exist, it was not a case of "Hey, we don't understand climate" and it was never a case of "it's getting cooler, an ice age must be coming." Rather it was uncertainty over which of two man-made influences would be the larger in coming decades: warming from CO₂ emissions, or cooling due to sulfate aerosols. This was a question in part because sulfate aerosol cooling and greenhouse gas warming do not cancel each other out, because their effects happen at different times and places. Aerosol cooling happens over polluted industrial areas in the Northern hemisphere, mainly during daylight hours in summer; while greenhouse gas warming has very little such variation. The two forces complicate one another, as opposed to canceling each other out.

In the 1970s when these discoveries were new, many weren't yet certain whether one or the other might win out. The warming effect of greenhouse gases was undisputed and had always been, but there was a new concern that the aerosol cooling might be even larger, at least in the short term. At a basic level, all the news reporting about global cooling can be traced back to this specific question.

But also during the 1970s, nations worldwide took drastic steps to reduce acid rain and sulfate emissions. The sulfate aerosols cleared up pretty quickly, and those who wondered whether their effect might trump warming quickly had their answer. It is absolutely still an important variable in our prediction models, but we no longer have the concern that some did in the 1970s that sulfate aerosol cooling might have a greater impact than greenhouse gas warming.

One gauge of the spread of the uncertainty of the 1970s was a 2008 study in the Bulletin of the American Meteorological Society titled The Myth of the 1970s Global Cooling Scientific Consensus. It was a survey of climate articles published between 1965 and 1979 in the scientific literature, rather than of those published in the mass media. The authors found that 10% of the articles did indeed predict cooling, 28% found the data insufficient to make a prediction either way, and 62% predicted global warming. In other words, 90% of climate articles in scientific journals in the 1970s did not conclude the Earth was cooling. Pretty much the opposite of how it was portrayed in the popular mass media, which shouldn't surprise anyone whose profession is science communication.

Even Exxon, a major fossil fuel company, was well aware in the 1970s that global warming caused by carbon dioxide from their product was potentially catastrophic. Like all oil companies, Exxon employed a battalion of climate scientists to help them strategize their future, and they needed to know as accurately as possible what the future held. In 2015, Inside Climate News concluded an eight month investigation into what Exxon knew in the 1970s and what they did about it. One internal Exxon memo from 1978 said:

What is considered the best presently available climate model for treating the Greenhouse Effect predicts that a doubling of the CO₂ concentration in the atmosphere would produce a mean temperature increase of about 2°C to 3°C over most of the earth... Present thinking holds that man has a time window of five to ten years before the need for hard decisions regarding changes in energy strategies might become critical. (Black, 1978)

Exxon's scientists did their best to pitch the importance of these studies to management:

The rationale for Exxon's involvement and commitment of funds and personnel is based on our need to assess the possible impact of the greenhouse effect on Exxon's business... In addition, the international significance of the proposed programs will enhance the Exxon image in the public domain and provide great public relations value. (Shaw, 1978)

For me, the single most compelling time capsule showing what the scientific community believed in the 1970s is found in the National Academy of Science's 1977 publication Energy and Climate: Studies in Geophysics. It's a sizable tome, but well worth the free download if you have a few hours (or weeks) to kill. Its ten chapters cover worldwide energy consumption, natural climate changes, industrial particulates and gases, energy transfer in the oceans, and climate modeling, and throughout it all runs constant study of CO₂ levels. Its 62 authors represented most of the major research universities, institutions, and agencies in the United States.

If this report can be taken as a fair assessment as the best state of our knowledge at the time (and I would argue that it can), then it is indeed fair to say that there was less agreement in the 1970s than there is now. But let us be very clear on what the range of that disagreement was. I offer the following paragraph from the report's foreword:

It will be noted that there are differences in the quantitative results of models developed by Revelle and Munk, by Keeling and Bacastow, and by others for partitioning carbon dioxide among the atmosphere, the oceans, and the biosphere. What is important is not that there are differences but that the span of agreement embraces a fourfold to eightfold increase in atmospheric carbon dioxide in the latter part of the twenty-second century. Our best understanding of the relation between an increase in carbon dioxide in the atmosphere and change in global temperature suggests a corresponding increase in average world temperature of more than 6°C, with polar temperature increases of as much as three times this figure. This would exceed by far the temperature fluctuations of the past several thousand years and would very likely, along the way, have a highly significant impact on global precipitation.

There was no fear of global cooling. None. Not even a whimper of trepidation. The sulfate aerosol cooling was absolutely discussed, and the authors were clear that the extent of its effects were not yet known, but there was no suspicion that it might trump greenhouse gas warming. Forty years later we have a lot more data from a lot more sources around the world, and we've been able to focus the probabilities to tighter ranges. The foreword continued:

If the preliminary estimates of climate change in the latter part of the twenty-second century are validated, a reassessment of global energy policy must be started promptly because, long before that destined date, there will have been major climatic impacts all over the world.

So there you have it. Yes, there were a lot of predictions of an oncoming ice age in the popular mass media in the 1970s, and there was some uncertainty in the climatology community due to insufficient data; but the fundamental observation that dominates today's climate science — that global warming is happening and is driven by manmade carbon dioxide emissions — was as real then as it is today. That this prediction has only become more thoroughly substantiated since Leonard Nimoy told us otherwise is a strength of the theory, not a weakness.

By Brian Dunning
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