Were they really predicting an ice age in the 1970s?

One common trope among climate change deniers is to point out that, in the 1970s, everyone was a panic about global cooling, even to the point of predicting an imminent ice age. If they were so spectacularly wrong back then, the argument goes, why should we be listening to them today?

The argument rests on an equivocation. In the 1970s, "they" refers to a handful of scientists making tentative predictions, and a handful of journalists who repeated those predictions. Today, "they" refers to every single major scientific body in the world. There's just no valid comparison.

In fact, back in the 1970s, more scientists were worried about global warming than its opposite. As USA Today reported last year, Thomas Peterson of the National Climatic Data Center surveyed 71 peer-reviewed articles from 1965 to 1979 and found that only seven predicted falling temperatures. Some 44 predicted warming, and another 20 were neutral.

William Connolley, a climate modeler with the British Antarctic Survey, has attempted to collect everything that was written in the scientific and popular press about global cooling in the 1970s and compile it on a single Web page. That page is about as long as the one you are viewing right now.

Try doing the same with everything written about global warming. How long would that page be?

Still, the notion that planet was cooling wasn't completely off base back then. At the time, scientists had just discovered that ice ages tend to occur in regular cycles (due in part to a slight wobble in the earth's axis). More importantly, there was a cooling trend from the 1940s to the 1970s, caused in part by soot and other aerosols blocking out the sun and temporarily muting the effects of greenhouse gases. But in the 1960s and '70s, pollution regulations kicked in and the air cleared, allowing the greenhouse effect to resume heating the globe.

But if you're a denier, don't take it from us. Here's MIT climatologist Richard Lindzen – one of the few climate- change skeptics with credentials in the subject – writing for the Cato Institute in 1992:

Indeed, the global cooling trend of the 1950s and 1960s led to a minor global cooling hysteria in the 1970s. ... But the scientific community never took the issue to heart, governments ignored it, and with rising global temperatures in the late 1970s the issue more or less died.

In short, science isn't monolithic. For instance, when a handful of prominent scientists gather in California to discuss the possibility of machines outsmarting humans, there's no need to panic just yet. But if every major scientific institution in the world were to warn of an imminent robot uprising, then it's time to take the battery out of your Roomba.