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Today scientists are warning of a warming planet - but didn't they claim a new ice age was on the way just 40 years ago? Sarah Lewis gets in a time machine and takes a look at the science of the 1970s.

In the 1970s, scientists predicted an ice age.

Nearly 40 years later, there is worldwide alarm as we are repeatedly warned of catastrophic warming to our climate.

Those who seek to undermine climate scientists are very quick to latch on to the idea that scientific thinking was so drastically different only a few short years ago.

Professor Callum Frith is the head of the School of Environment and Technology at the University of Brighton. He studied physical geography at Aberystwyth in the late-1970s, before gaining a doctorate in sea-level changes and glaciers from the University of Coventry.

He says: "I remember a lot of talk about the Big Freeze in the media.

Astronomer Fred Hoyle brought out his book talking about instantaneous glacerisation. There were articles in The Observer and a variety of papers.

"But Hoyle published a number of books in fields which aren't really his subject area. He picked up information from what was going on in geography and geology research, which talked about moving into the next ice age."

It transpires what those geography and geology researchers were talking about was not quite the strong ice-age prediction popular urban legend would have us believe.

ICE-AGE MYTH BORN OF FACT
Climate science is a fairly new field of study. The 1970s saw a revolution in scientific thinking which precipitated the birth of modern-day climatology.

Professor Frith says: "It was one of those scientific moments where it all suddenly changes and, as a consequence, a lot of new research takes place. There was a seminal paper published in 1971 which took us from the idea of having had four ice ages with long warm periods in between to having had 18 to 20 ice ages with the warm periods being very short and the ice ages an awful lot longer.

"Subsequently, we showed we can go from the sort of conditions we have at the moment to cold periglacial - southern England would be like northern Norway - within 30 years. So within a generation you're going from lovely warm conditions and deciduous trees to arctic tundra.

"No one had realised you could have such rapid environmental change and that is very dramatic. The Press picked up on the idea of instant glacierisation as being an interesting topic."

IT WAS NEVER NEXT WEEK'
The 1971 paper, coupled with a new understanding of variations in global temperature caused by a wobbly planetary orbit (Milankovitch Cycles), meant scientists could begin predicting when the next ice age might be.

They found we are probably already past the peak of this interglacial period and we are, indeed, heading towards a new period of cooling.

In 1976, an American climate prediction project said that, without any man-made warming, "The longterm trend over the next several thousand years is toward extensive Northern Hemisphere glaciation."

There was also mention at the time of a phenomenon called global dimming, caused by aerosols and pollutants in the atmosphere stopping light and heat hitting the planet.

However, the warming effects of carbon dioxide and other greenhouse gases were also known.

In fact, as far back as 1896, Swedish scientist Svante Arrhenius calculated that doubling atmospheric carbon dioxide would raise global temperatures five to six degrees Centigrade.

What was not known in the 1970s was whether the cooling or the warming would have a dominant effect.

WHAT 1970S SCIENTISTS SAID
A study to be published in The Bulletin Of The American Meteorological Society looks at peer-reviewed scientific journals from the period 1965 to 1979. It says: "A review of the literature suggests that... greenhouse warming even then dominated scientists' thinking about the most important forces shaping Earth's climate on human timescales."

The report found, of the papers reviewed, only seven discussed cooling, while 20 were neutral in their predictions and 44 predicted warming.

It also found, "When the myth of the 1970s global-cooling scare arises in contemporary discussion over climate change, it is most often in the form of citations not to the scientific literature, but to news media coverage... Even a cursory review of the news media coverage of the issue reveals that, just as there was no consensus at the time among scientists, so was there also no consensus among journalists."

Indeed, according to their press office, even the BBC has no record of stories relating to "the Big Freeze" in their archives.

POLITICAL MISQUOTING
But the proliferation of the idea of a great ice age continues - and this may well be blamed on a particularly potent misquote from a report by the National Science Board in 1972, used in both the Washington Post and the United States Senate in 2003.

It says: "Judging from the record of the past interglacial ages, the present time of high temperatures should be drawing to an end, to be followed by a long period of considerably colder temperatures leading to the next glacial age."

The part of the report not quoted, and which follows on immediately from this, reads "...some 20,000 years from now. However, it is possible, or even likely, that human interference has already altered the environment so much that the climatic pattern of the near future will follow a different path.

"For instance, widespread deforestation in recent centuries, especially in Europe and North America, together with increased atmospheric opacity due to man-made dust storms and industrial wastes, should have increased the Earth's reflectivity.

At the same time, increasing concentration of industrial carbon dioxide in the atmosphere should lead to a temperature increase."

SO, THAT'S IT, FOLKS
It is easy to see where the confusion lies. An ice age was predicted, but using the geological definition of "imminent", some 20,000 years in the future, rather than the colloquial one, which would suggest any time in the next few years.

Although warming is now the issue, the original science which suggested cooling is by no means invalid. Rather, it is the foundation on which modern climatology sits.

David Roberts is a green politics and culture journalist. On this topic he says: "For a while, a few (not most) scientists thought one set of factors would outweigh another. We now know they were badly wrong. This isn't some sort of embarrassing gotcha. It's progress.

It's how human beings figure stuff out.

It's how science works."

10:47am Monday 21st April 2008

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