What do scientists know about global warming? In the 1970s, they predicted a coming ice age, right? Not quite. Owen Amos discovers why experts soon weren't so hot on the idea.

"The ice age is coming, the sun's zooming in Meltdown expected, the wheat is growing thin Engines stop running, but I have no fear 'Cause London is drowning and I live by the river." - London Calling, by The Clash (1979)

THE warning is stark. "There are ominous signs that the earth's weather patterns have begun to change dramatically," the article says. "And that these changes may portend a drastic decline in food production - with serious political implications for just about every nation on earth. The regions destined to feel its impact are the great wheatproducing lands of Canada and the USSR in the north, along with a number of marginally selfsufficient tropical areas - parts of India, Pakistan, Bangladesh, Indochina, and Indonesia. The evidence in support of these predictions has now begun to accumulate so massively that meteorologists are hard-pressed to keep up with it."

Another doomsday declaration on global warning? Another finger-wagging lecture, insisting we drive less, move less, and use less? Not quite.

The article, from Newsweek on April 28, 1975, is on climate change. But it's titled "The Cooling World". It warns "English farmers have seen their growing season decline by two weeks since 1950", and "after three quarters of a century of extraordinarily mild conditions, the earth's climate seems to be cooling down". The piece even suggests two solutions: divert arctic rivers, or melt ice caps with soot.

The author was a journalist. And yet, global cooling was endorsed by many - though not all - scientists. In 1971, for example, S Ichtiaque Rasool and Stephen H Schneider, suggested increased aerosols - particles in the atmosphere - could decrease temperatures and "trigger an ice age". In the same year, Paul Anderson's book, "Omega - Murder of the Ecosystem and the Suicide of Man", put forward solutions, including a 50-mile long Bering Strait dam, to increase warm water in the Arctic. A 1976 book, The Cooling by Lowell Ponte, said cooling could cause world wars by 2000.

So why did we consider global cooling? Because, quite simply, the world was getting colder. In the 20th Century, until 1945, temperatures increased by 0.5C in total. Then, until 1970, they started dropping by around 0.2C. Asia and North America had harsh winters in 1972 and 1973. Scientists, and others, wondered why. There were two main theories.

FIRSTLY, some thought the earth's tilt - thought to be responsible for ice ages - was changing, causing less sunshine to reach earth. Secondly, aerosols - caused, for example, by burning fossil fuels - block sunlight reaching earth's surface.

"One particular piece of work was done around the mid-1970s," says Professor Brian Huntley from Durham University's School of Biological and Biomedical Sciences. "A young lady called Genevieve Woillard had been working on a core from a bog, called the Grand Pile. For the first time, she found a record of the whole of the last interglacial period - the last time the climate was comparable to what we have enjoyed for the past 10,000 years or so. She found the end of the last inter-glacial appeared to happen very quickly - in much less than 1,000 years, and probably just a few centuries. Very quickly, it went from being mild, like now, to glacial.

"At the same time, a German found a record of annual bands of sediment and estimated the last inter-glacial lasted ten to 11,000 years. People got hold of that, and the fact that the last inter-glacial ended quickly, and thought: A-ha. Our inter-glacial has lasted 10,000 years, it must be near the end, it's going to get cold'. It wasn't great science, but it was picked up by the media."

However - while some predicted an ice age, plenty didn't. Thomas C Peterson, William M Connolley, and John Fleck, recently reviewed all climate science literature from 1965 to 1979 and found just seven articles indicating cooling. At least 42 indicated warming. The media wasn't convinced, either. A year before Ponte's The Cooling, for example, the book Hothouse Earth by Howard Wilcox was published.

"An enduring popular myth suggests in the 1970s the climate science community was predicting global cooling' and an imminent' ice age," say Peterson, Connolley and Fleck. "A review of the literature suggests that, to the contrary, greenhouse warming even then dominated scientists' thinking."

In the 1970s, scientists thought aerosols could make the earth colder and that carbon dioxide could make it warmer. Simply, they didn't know which would have most effect. The indecision didn't last long. Today, global warming - as if you needed reminding - is the consensus.

Prof Huntley, for one - while accepting "all theories can be overturned" - believes today's science is sturdier. "The evidence in the 1970s was much slenderer," he says.

"I think the overwhelming evidence we have points to the fact that global warming is happening, and we are more secure in our understanding of what's going on. If we continue to add gases to the atmosphere in the way we are, the upward trend (of temperatures) is expected to continue."

So what about Britain's absolute absence of summer last year? What about China's worst snow in 50 years? Or Afghanistan's worst snow in 30 years? Or snow in Saudi Arabia, and temperatures of -31c in Greece? What about UN meteorologists predicting that 2008 will, in fact, be colder than last year?

"There is inherent variability - and we are expecting there to be perhaps even more variability," says Prof Huntley. "I remember the Great Drought of 1976, where we were using bath water to water the garden; the winter of 1962 with weeks and weeks of snow in our garden in Low Fell, Gateshead. These things are part of the natural variability of the climate. The fact that this year is a lot cooler is part of that expected variability."

In 2006, Newsweek wrote an article on its own 1975 piece. It was, it said, "spectacularly wrong about the near-term future".

"Predictions of global cooling never approached the kind of widespread scientific consensus that supports the greenhouse effect today," it wrote.

"And for good reason - the tools scientists have at their disposal now render any forecast from 1975 as inoperative as the predictions being made around the same time about the inevitable triumph of Communism."