A key argument climate skeptics always rely on is the now debunked prediction of a ‘new ice age.’ But the story of that 1970s debate is compelling as current evidence of global warming.

In any debate about climate change — and more importantly, its potential impact on agriculture — there are always skeptics who try to deflect the debate by noting that “In the 1970s, these scientists were predicting global cooling.”

The implication being, they didn’t’ know what they were talking about then, and they don’t have any credibility now.

It’s true that a number of scientific studies in the 1970s discussed the threat of an ice age that might occur in the future, including an influential 1971 paper by Stephen Schneider, then a climate researcher at NASA's Goddard Space Flight Center in Maryland. Schneider suggested that the cooling effect of “dirty air,” due to ongoing particulate pollution (the major provisions of the Clean Air Act of 1963 had only begun to be implemented at that time) could outweigh the potential warming effect of CO2.

The other contributing factor at the time, for those who remember their eco-history, was a growing fear that the ozone-destroying propellants in aerosol products would aggravate global warming.

In essence, it was an intellectual battle over warming versus cooling.

According to a comprehensive review in the New Scientist magazine published a few years ago, “There was a chill across the world [back then], and it wasn’t just the cold war. From the 1940s to the mid-1970s, the planet seemed to be in the grip of a global cooling. For a while, almost every outbreak of extreme weather was blamed on it [by] members of the new scientific discipline, climatology.”

However, here’s a bit of history everyone does remember.

Seventy-five years ago, global cooling was real, not some theoretical phenomenon. In the summer of 1941, Hitler’s blitzkrieg had swept across most of Western Europe and the Nazis were pounding the Russian army as it pushed toward Moscow.

As a BBC history of the campaign on the Eastern Front noted, “One week into the German invasion, 150,000 Soviet soldiers were either dead or wounded. As the German armies swept further into the Russian heartland, [the city of] Kiev fell to the Nazis wehrmacht and 600,000 Soviet soldiers had been captured. By October 1941, three million Soviet soldiers were prisoners of war.”

But as historians have noted, the winter of 1941-42 was one of the most severe in decades, and the heavy snow and bitter cold accomplished what Stalin’s Red Army could not: inflicting a crippling defeat on Hitler and changing the course of World War II.

Reversal of opinion

Even before the 1970s were out, average global temperatures began to rise, and many of scientists who had been predicting an ice age now began warning about global warming instead. Plenty of critics now use that reversal as the basis for arguing that climate scientists are simply scaremongers and shouldn't be believed, then or now.

As the UK’s The Guardian reported, as the decade came to a close, Schneider (and other climate scientists) realized that climatologists had “overestimated the cooling effect of aerosol pollution and underestimated the effect of CO2, meaning warming was more likely than cooling in the long run.”

In his review of a 1977 book called “The Weather Conspiracy: The Coming of the New Ice Age,” Schneider acknowledged that, “We just don’t know . . . whether we are in for warming or cooling — or when.”

A New Scientist story also noted that between 1965 and 1979, 44 scientific papers predicted global warming, 20 were neutral and just 7 predicted global cooling. “So while predictions of cooling got more media attention, the majority of scientists were predicting warming even then,” according to the story.

The current scientific consensus on human-induced global warming, however, is based on a significant body of research by thousands of scientists over more than 50 years — all of put under intense scrutiny by other scientists, energy industry lobbyists and a veritable horde of professional skeptics and conspiracy believers.

The fight over whether predictions of a new ice age decades ago were legitimate or not is a moot point. The data on rising average temperatures is conclusive, although the aforementioned “horde” continues to insist that the phenomenon is part of the “natural climate evolution.”

Although climate doesn’t “evolve” in one generation.

But it’s important to chill out on the subject, so that productive debate can resume — not over whether we’re facing potentially devastating change in the world’s climate, but about how best to respond before agriculture gets permanently damaged.

Along with the rest of civilization.

The opinions expressed in this commentary are solely those of Dan Murphy, a veteran food-industry journalist and commentator.