In Wisconsin, the governor has declared a state of emergency, and many school districts called off classes ahead of a bone-chilling week of weather. The looming deep freeze led to federal court closures in Chicago and shut down the Lincoln Park Zoo — though polar bears will still be allowed outside. Flights were grounded. Amtrak canceled trains running in parts of the Midwest. Utility companies scrambled 24-hour response teams, because as one executive told The Post, “In these kinds of events, people just cannot be out of power.”

As millions of people across the nation braced for a possibly life-threatening cold snap, President Trump late Monday used the opportunity to mock the idea that climate change is actually happening, while misspelling the word “warming.”

“In the beautiful Midwest, windchill temperatures are reaching minus 60 degrees, the coldest ever recorded. In coming days, expected to get even colder,” Trump tweeted. “People can’t last outside even for minutes. What the hell is going on with Global Waming? Please come back fast, we need you!”

The president has often used the weather of the moment, rather than long-term changes in the climate, to spread skepticism of the widely held consensus among scientists that the world is warming at an alarming pace. In reality, tweets like this one confuse the difference between climate and weather (weather happens in a given place and time; climate is the average of weather over time).

"Even in a warming climate, you still expect to get extreme and sometimes record lows occurring — they’ll just be occurring less frequently,” said Andrew Dessler, a professor of atmospheric sciences at Texas A&M University, noting that recent years have brought many more record highs than record lows.

“As far as the president’s remark, I’m not sure exactly what to make of it," he said. "But I think in this case Trump’s signaling to his base that he doesn’t take climate change seriously.”

Indeed, in this particular case, counterintuitive as it may sound, some scientists say the so-called “polar vortex” descending over the Midwest and Great Lakes Region is the kind of event we should expect more of as the Arctic gets severely disrupted by climate change.

Granted, that’s far from an established point of view. Other researchers continue to demur about a winter weather event that could be historic in the cold it brings to some regions.

“I think this a really interesting, open question that is very much on the cutting edge of climate science,” said Michael Mann, a climate scientist at Pennsylvania State University.

For nearly a decade, there have been scientific contentions that the rapid melting of the Arctic, which is happening much faster than the warming of more temperate latitudes, is interfering with weather, especially in winter.

These contentions have drawn a lot of attention. The Obama administration, for instance, put out a 2-minute video explaining the 2014 polar vortex, taking pains to say that frigid weather doesn’t mean the Earth’s atmosphere isn’t warming. “If you’ve been hearing that extreme cold spells like the one we’re having in the United States now disprove global warming, don’t believe it,” John Holdren, Obama’s top science adviser, said at the time. “The fact is that no single weather episode can either prove or disprove global climate change.”

U.S. winters themselves in the past decade have shown sometimes dramatic cold spells and massive snow events that seem hardly what you would expect from a warming climate. But some scientists have argued that the culprit is actually the fast-warming Arctic.

As the Arctic warms, the changes can interfere with the atmosphere well beyond the region. A case in point is very low levels of ice in the Barents and Kara Seas north of Scandinavia and Russia that have been observed recently — the Barents is unusually ice free.

That lack of ice unleashes warmth from the ocean, and this creates a region of high pressure, said Judah Cohen, who directs seasonal forecasting at the firm Atmospheric and Environmental Research. In turn, the jet stream — the river of air that flows from west to east across the northern hemisphere — forms elongated waves that dip farther to the south, and also reach farther north.

“The waviness means that there can be increased, larger excursions of cold air southward — that is, into the mid-latitudes,” Holdren said, in explaining the polar vortex in 2014.

Jennifer Francis, a Rutgers climate scientist and Arctic expert who has been perhaps the single most influential voice for the idea that climate change causes crazy winters, agrees with that explanation.

“In this case, and last winter, it seems to be a very clear example of the sea ice being extremely low in this particular part of the Arctic,” Francis said, adding, “and that’s why there’s a connection to climate change.”

But not everyone is convinced.

There has been a clear trend toward more disturbances of the polar vortex in the past several decades, said Jason Furtado, a meteorologist at the University of Oklahoma. But it’s hard to fully attribute that to climate change.

“I’m not 100 percent convinced that this weakening trend is related to climate change only,” said Furtado. “I think there is evidence that the vortex goes through these strong and weak cycles naturally. So it’s hard to disentangle cause and effect cleanly right now.”

One thing is clear: Whether climate change is influencing these events, there is certainly no argument against climate change.

When the polar vortex splits and travels southward, warm air simultaneously invades the Arctic — so while some regions experience unusual cold, others get unusual warmth. That’s different from the uniform cooling of the sort that might truly challenge the idea of climate change.

It’s also important to note that, whatever is going on with the polar vortex, these events are episodic, and the overall winter trend makes sense — it is one of warming.

In the Southern Hemisphere, where it is summer, Australia has been breaking all-time heat records. There are reports of horses dying in droves as temperatures in some spots reach 120 degrees.

Even the National Oceanic and Atmospheric Administration on Tuesday tweeted that “winter storms don’t prove that global warming isn’t happening.”

In the United States, the coming cold has triggered angst — and action.

“This is a big event for us,” said Anne Pramaggiore, head of Exelon’s utility businesses, which provide power to about 22 million people, including in Illinois and other places facing brutal cold this week. “We understand how critical our service is for customers during a time like this.”

She said the company has been beefing up round-the-clock crews, inspecting substations and other infrastructure and doing whatever it can to ensure reliability. “What you’re really concerned about is keeping the system up and running so that you don’t have people without power in these kinds of situations,” she said.

The Bishop Dudley Hospitality House, a shelter in Sioux Falls, S.D., has room for 80 men, 20 women and seven families. But this week, with wind chills set to reach minus-50 or below, workers are preparing to put cots and mats in any spare corner, determined that anyone seeking refuge can find it.

“We do not turn people away,” said Amanda Stidd, the shelter’s development coordinator. “Our number one priority is to make sure that no one gets left outside.”

Meanwhile, one Michigan police department managed to find a sliver of humor in the ridiculously cold weather descending over the region.

“Due to unexpected freezing temperatures, The Romulus Police Department will be cancelling all crime, both felonies and misdemeanors,” the department wrote recently on its Facebook page. “So bad guys, if you have to commit a crime, please wait until spring, or at least until temperatures are warmer than a polar bear’s toenails.”