On Thursday, Rep. Alexandria Ocasio-Cortez of New York and Sen. Ed Markey of Massachusetts introduced what many news outlets ­described as “legislation” for the Green New Deal, a wildly ambitious plan to eliminate the American fossil-fuel industry within a decade or so. It’s worth noting that it isn’t legislation as people normally understand the term. It’s a resolution titled “Recognizing the Duty of the Federal Government to Create a Green New Deal.” In other words, even if it passed — a considerable if — nothing would really happen.

House Speaker Nancy Pelosi isn’t taking it too seriously. She didn’t put Ocasio-Cortez on the new Select Committee on the Climate Crisis, and when asked about the resolution, she was dismissive.

“It will be one of several or maybe many suggestions that we receive,” Pelosi said. “The green dream or whatever they call it, nobody knows what it is, but they’re for it, right?”

I bring this up for the simple reason that a lot of people on the left and right have every incentive to make this thing a much bigger deal than it is.

Still, given that almost every candidate running for the Democratic presidential nomination feels obliged to support the Green New Deal, it’s worth taking somewhat seriously.

This raises the first of several problems: It isn’t a very serious proposal. The goal is to eliminate the fossil-fuel industry over a decade and, perversely, phase out nuclear power over a slightly longer period. All of the jobs dependent on these industries would be replaced by government-guaranteed jobs.

“We set a goal to get to net-zero, rather than zero emissions, in 10 years,” the backers explain in an outline, “because we aren’t sure that we’ll be able to fully get rid of farting cows and airplanes that fast, but we think we can ramp up renewable manufacturing and power production, retrofit every building in America, build the smart grid, overhaul transportation and agriculture, plant lots of trees and restore our ecosystem to get to net-zero.”

Well, at least the plan isn’t too ambitious. Retrofitting “every building in America” can be done in 10 years, but eliminating all the gassy cows will take a little bit longer. Maybe we’ll move them all to ­Hawaii, which, with the near-abolition of airplanes, would be ­effectively cut off from America anyway.

Even if you take these goals seriously, as a practical matter it’s a fantasy masquerading as green virtue-signaling.

But it’s a fantasy based on a worldview that should be treated seriously, because it’s so dangerous. National Public Radio’s Steve Inskeep asked Ocasio-Cortez whether she was comfortable with the “massive government intervention” critics say is required by such an undertaking.

“We have tried their approach for 40 years,” Ocasio-Cortez replied. “For 40 years we have tried to let the private sector take care of this. They said, ‘We got this, we can do this, the forces of the market are going to force us to innovate.’ Except for the fact that there’s a little thing in economics called externalities. And what that means is that a corporation can dump pollution in the river and they don’t have to pay for it, and taxpayers have to pay.”

The fascinating thing is that ­Ocasio-Cortez thinks this is actually true.

Thanks to the government intervention known as the Clean Water Act and other regulations, corporations can’t pollute waterways. Ironically, the only entities that can pollute with impunity are government agencies, such as the Environmental Protection Agency, which did precisely that in Colorado in 2015.

Closer to home, ExxonMobil has spent millions cleaning up Newtown Creek, which happens to run through Ocasio-Cortez’s native Brooklyn, close to her district. Ironically, New York City is still allowed to pollute the creek whenever there’s a heavy rainfall.

Even if Ocasio-Cortez was speaking figuratively in her talk of “externalities,” the larger point remains. The free market hasn’t been given free rein, and over the last 40 years the free market and government regulations alike have made laudable environmental progress. In 2017, the US had the largest reductions of CO2 emissions in the world for the ninth time this century.

Rather than celebrate and build on that reality, the Green New Dealers would rather embrace their fantasies — and waste a lot of time and money in the process.