“Civilization will end within 15 or 30 years unless immediate action is taken against problems facing mankind.”

Sounds dire. A reaction to the National Climate Assessment published the day after Thanksgiving? No. Harvard biologist George Wald made that claim in 1970.

So if Wald had been correct, just about everything would have crumbled to ruin sometime between 1985 and 2000.

Wald, however, wasn’t alone. He and others came up with some incredibly over-the-top predictions as the 1960s came to a close.

“Earth Day” founder Denis Hayes, for example, didn’t hedge his bets: “It is already too late to avoid mass starvation.” Or take Paul Ehrlich (please). The author of 1968’s “The Population Bomb” was another gloom-and-doom prophet who made so many failed predictions over the years that it’s almost hard to keep count.

“Population will inevitably and completely outstrip whatever small increases in food supplies we make,” he said in a 1970 interview. “The death rate will increase until at least 100-200 million people per year will be starving to death during the next 10 years.”

Off by about 180 degrees. Food production spiked in the ensuing years. And starvation on such a massive scale never materialized, thank God.

Many other examples could be cited (I haven’t even touched on predictions by global-warming luminaries such as Al Gore), but I hope the point is clear: Take sky-is-falling claims with a large grain of salt.

Particularly because they never seem to go out of style. You’d think, given the track record I’ve just referred to, that doomsayers would learn to temper their warnings, at least a little bit. But no. We see the same trend at work with the National Climate Assessment.

“Global greenhouse gas emissions is expected to cause substantial net damage to the U.S. economy throughout this century,” we read in the 1,700-page report.

How substantial? As The New York Times noted: “All told, the report says, climate change could slash up to a tenth of gross domestic product by 2100, more than double the losses of the Great Recession a decade ago.”

Sounds awful, to put it mildly. Then again, so did the first Earth Day predictions. And these latest claims are just as plausible, according to climate expert Nicolas Loris.

“The study … calculates these costs on the assumption that the world will be 15 degrees Fahrenheit warmer,” he writes. “That temperature projection is even higher than the worst-case scenario predicted by the United Nations Intergovernmental Panel on Climate Change.
“In other words, it is completely unrealistic.”

So where do these Chicken Little claims come from? In the report, climatologists lay out four possible future trajectories for the environment. Alarmists seized on the worst one.

It’s also the least likely. It assumes a combination of bad factors will somehow coincide — that global population will climb at the fastest-possible rate (about double the current amount), that technology will develop at the slowest-possible rate, and that world poverty will increase massively, along with energy use and emissions.

Would it be responsible to assume the best-case scenario? Of course not. But assuming the worst-case is no better. In fact, considering the policy changes that believers wind up pushing as a result – such as huge carbon taxes and giant subsidies for dubious “green” projects — it’s even less responsible.

Not that the alarmists need an excuse like the National Climate Assessment to make bad recommendations. Even before it came out, the Intergovernmental Panel on Climate Change had proposed a carbon tax of between $135 and $5,500 per ton of carbon emissions by the year 2030.

“An energy tax of that magnitude would bankrupt families and businesses, and undoubtedly catapult the world into economic despair,” Mr. Loris writes.

If the doomsayers want to spread pessimism, that’s their business. But the rest of us shouldn’t have to pay for it.

It’s time for the global-warming crowd to realize, once and for all, that civilization isn’t ending – not in 1985 and not in 2100. And those are the cold facts.