Greta Thunberg, Joaquin Phoenix and fellow eco-luminaries used Earth Day Wednesday to rejoice in the global economic shutdown that has led to a reduction in carbon emissions.

The pandemic has been a dream come true for climate alarmists . . . if you ignore all the misery.

They wanted us to switch off our economies to prevent a supposed climate apocalypse in 10 years and — hey, presto! — their wish was granted by a virus.

Thunberg, the 17-year-old Swedish climate evangelist, did caution her fellow warriors not to be too “optimistic” about the pause in carbon pollution because the ­so-called climate crisis “is not slowing down.”

But other activists seized the pandemic opportunity to push their agenda, as Democrats tried to shoehorn their Green New Deal into economic relief bills.

“Neither Greenpeace, nor Greta Thunberg, nor any other individual or collective organization have achieved so much in favor of the health of the planet in such a short time,” Spanish scientist Martín López Corredoira crowed on the Science 2.0 blog.

“A miracle happened . . . It is certainly not very good for the economy in general, but it is fantastic for the environment.”

It sure is a high price to pay for the dubious benefit of temporarily reducing greenhouse gas emissions.

But that is the price climate alarmists have been demanding, to slash emissions by crippling our economies in an uncertain bid to dial down Earth’s temperature. Now we see what that means.

One thing the pandemic has shown us in real time is how inaccurate computer models are and their sensitivity to variations in ­inputs.

Whether it’s the coronavirus or global warming, these models are chronically unreliable at predicting the future.

We have seen that projections of as many as 2 million American deaths from the coronavirus were wrong by orders of magnitude.

The models that were used to inform decisions to freeze the economy are being revised as new data come to hand.

At the start of this month, the president’s coronavirus task force announced that between 100,000 and 240,000 Americans likely would die from COVID-19, even with mitigation measures.

The projections led to President Trump extending the lockdown that has seen more than 20 million Americas filing for unemployment.

But the models on which the task force based its advice to the president varied widely.

One, from the University of Washington, initially projected up to 162,000 deaths over the summer, before being revised down.

The most extreme was a model from Imperial College London, which predicted a staggering 2.2 million Americans would die if there were no social-distancing measures.

Last month, the projection was downgraded to 200,000 due to successful mitigation and testing data indicating that more people have been infected than previously thought.

By Wednesday, with the rate of infection plateauing, America had suffered almost 47,000 deaths, while projections have been ­revised to around 60,000. So you can see that computer modeling is an imperfect science.

But none of this is to criticize the models used to manage the pandemic, because they are built to change as inputs change.

They are valuable, not to predict the future but to test potential scenarios.

There was so much we didn’t know at the beginning of the pandemic and there were so many variables, from the infection rate and immunity levels to the take-up of social distancing

As we learn more, the models are updated and the projected death toll falls.

That’s the way it’s meant to work. Task force expert Dr. Anthony Fauci has said a model is just a “hypothesis.”

When quizzed on Fox News two weeks ago about the reliability of the seesawing coronavirus models, he said they are “only as good as the assumptions that you put into the models.

“And those assumptions that start off when you don’t have very much data at all, or the data you have is uncertain, then you put these assumptions in and you get these wide ranges of calculations of what might happen.”

He told CNN, “I’ve never seen a model of the diseases that I’ve dealt with where the worst case actually came out. They always overshoot.”

Fauci is echoing the famous aphorism in statistics: “All models are wrong, but some are useful.”

So, having seen the fallibility of coronavirus models over the past few weeks, it stands to reason that we should treat climate models with the same skepticism, especially as the time span is so much longer.

Doomsday models predicting imminent climate calamity from the United Nations’ Intergovernmental Panel on Climate Change should not be used to remake our economies on blind faith or to terrify susceptible children like Greta Thunberg.

Computer models are not holy writ. They are just useful tools.

Demonizing legit ‘virus’ voices

An ugly demonization game is being played over the coronavirus.

Vice News has portrayed protests against the lockdown as the dastardly work of “white supremacists and neo-Nazis,” citing alarmist research by an outfit called Site Intelligence.

And Fox anchor Sean Hannity has been branded a killer by Vox news for his coverage of the coronavirus, citing a dubious study from the University of Chicago. “Why the finding that Sean Hannity killed people is disturbingly plausible,” wrote Vox.

This willful slander is pointlessly destructive.

NYCHA workers left imperiled

It’s all very well for Mayor Bill de Blasio to hand out free masks, meals, tablets and high-speed internet services to residents of New York City Housing Authority complexes.

But what about looking after the city workers risking their health to service NYCHA buildings that have become coronavirus hot spots?

Painters, plumbers, cleaners and caretakers complained for weeks about having to enter apartments without masks to make repairs.

Even after their unions intervened two weeks ago, the workers haven’t yet been provided with proper N95 masks.

Instead, they are handed a “flimsy paper mask” at the start of a shift, says one worker.

He claims his colleagues are “dropping like flies . . . More and more call out sick every day.

“Four men that I worked directly alongside, riding elevators with and inspecting stairwells with, have been hospitalized.

“I am unable to visit my family any longer for fear of exposing them.”

The city should be taking better care of these essential workers, or the problems at NYCHA will only get worse.