Many coastal city officials are considering spending millions — in some cases billions — of taxpayer dollars preparing for an impending flood caused by rising sea levels.

For example, in 2013, New York City Mayor Michael Bloomberg announced a $20 billion, 20-year plan to protect the city from rising sea levels.

The concerns are being driven in part by recent studies predicting the coming floods, such as two new reports that claim seas are rising faster than at any other point in the last 28 centuries. They contend if human-caused carbon emissions continue at the current rate, the oceans could rise by as much as four feet by 2100.

That conclusion is tame compared to a 2015 study by NASA’s former lead climate scientist, James Hansen, and others, who boldly predicted sea levels could rise by at least 10 feet in 50 years.

But notice there’s a 500 percent variance between the two predictions if we extrapolate so that both use the same end point. Given all the other important public policy challenges facing cities, such as providing good public education, safe communities and infrastructure improvements, shouldn’t city officials demand a little more scientific consensus on the magnitude of the threat?

They won’t get it.

And the reason is that such claims are not based on observed scientific data, but manmade computer models, which have overpredicted climate warming for decades.

For example, John Christy of the University of Alabama at Huntsville and the state’s climatologist, stated in congressional testimony that climate models have predicted two and a half times more global warming than has actually been observed by satellites and weather balloons.

And Roy Spenser, a former senior scientist for climate studies at NASA’s Marshall Space Flight Center, notes 95 percent of the climate models have overpredicted actual warming.

It’s like believing Uncle Harry’s frequent predictions of an imminent global economic collapse, not because he’s ever been right, but because he’s wrongly predicted it so often.

Yes, sea levels are rising, and have been since the end of the Ice Age some 11,700 years ago. But the observed sea level rise averages between eight and 10 inches over 100 years – which is a long way from four feet, not to mention 10.

The fact is that climate models are astonishingly unreliable, as even many climate scientists who support modeling concede.

As Mark Maslin and Patrick Austin, climate scientists at University College London, explained in the journal Nature in 2012: “Why do models have a limited capability to predict the future? First of all, they are not reality. This is perhaps an obvious point, but it is regularly ignored. By their very nature, models cannot capture all of the factors involved in a natural system, and those that they do capture are often incompletely understood.”

And remember, these are climate-model defenders.

Don’t misunderstand me: Rising sea levels can pose a threat to humans and property, as Hurricane Sandy amply demonstrated. Coastal city officials should be weighing the risks and costs of an effective response. But the public policy challenge is to accurately assess the nature and seriousness of the threat and act accordingly.

With respect to sea levels, the current threat comes primarily from humans moving closer to the sea, rather than the sea moving closer to humans.

People are willing to pay big bucks to live right on the ocean; but that means damage totals — in lives and money — can rise significantly during major storms and sea surges.

If past observed sea level trends continue, the ocean certainly could pose a significant threat to humans and property — in several hundred years. Is that worth spending billions of dollars now, when there are so many other important city priorities?