© Scott Olson/GettyMist rises from Lake Michigan on Jan. 6, 2014 in Chicago, Ill.
In the 2004 disaster-flick "Day After Tomorrow," abrupt man-made climate change knocks the planet into a state of utter chaos. At the time, the movie's vision of the apocalypse wasn't seen as realistic. But that's begun to change.

Two new studies deepen the fear that global warming could shut down the circulation of the oceans, much as the movie portrays, dropping vast stretches of Asia into drought and exposing the whole Northern Hemisphere to severe ice and snow.

Unlike gradual climate change, where the planet warms steadily, this change would be sudden and sharp enough to roil civilization—happening in as little as three years and resulting in as much as an 18-degree Fahrenheit drop in average temperatures.

Jud Partin is the lead author of the stronger, more ambitious of the two studies. He's also a geophysicist at the University of Texas, and an unabashedly close viewer of a certain summer blockbuster starring Dennis Quaid as hero-scientist Jack Hall.

"In the movie they defy the laws of physics. They have hurricanes developing over land and tornados in Los Angeles and other impossible stuff," Partin told MSNBC. "But they got the climate science pretty right."

The science deals with the "Atlantic thermohaline circulation," an oceanic conveyor belt that carries heat from the tropics to the north, where it warms Western Europe and Eastern North America. It's a fragile pattern, dependent on precise levels of salinity; Partin and others believe it could stop as Greenland's ice sheets melt, flooding the ocean with fresh water.

To glimpse our possible future, Partin and his colleagues gathered new geological data and re-examined the deep past. They looked at an earlier, all-natural melt-off that happened about 12,000 years. Known as the "Younger Dryas," the period was defined by a deep chill across the northern latitudes.

Ice core studies cited by Partin show an 18-degree Fahrenheit drop in average temperatures across Greenland. New York and London would be slightly warmer, he believes, but still frigid with average temperature drops of at least a dozen degrees. That might seem small, but even minute changes in the average are a signal of extreme swings in actual conditions.

And the effects of this climate change would be felt in a matter of years or decades, rather than a century or longer. That's because this part of the climate system seems to work more like a switch than a dial. Once a certain threshold is reached, there's a big, fast swing in the conditions over large parts of the planet.

"It would definitely change everyday life in Europe and North America," Partin told MSNBC. "Daily life would be drastically affected in these areas, in ways I can't imagine or begin to address."

Some climate change deniers might want to use Partin's research - which focuses on cooling rather than warming - to claim that scientists can't make up their minds about climate change or that it won't be hot or dangerous. They'd be wrong to assume that.

The script of "The Day After Tomorrow" does a decent job driving a stake through the issue.

"Yes, it is a paradox, but global warming can trigger a cooling trend," says Dennis Quaid, launching into some on-screen exposition as the scientist Jack Hall.

"The Northern Hemisphere owes its climate to the North Atlantic Current," Dr. Hall explains. "Heat from the sun arrives at the equator and is carried north by the ocean. But global warming is melting the polar ice caps and disrupting this flow," he continues. "Eventually it will shut down. And when that occurs, there goes our warm climate."

Parts of the movie are gross exaggerations that Partin says we don't have to worry about, like unrelated extreme weather events and speeding up the time frame for change. The cooling, for example, happens in a matter of days, instead of years or more likely decades. The freeze is also deeper, with North America covered in glaciers almost overnight.

But in other ways the movie arguably doesn't go far enough. Shortly before the release of "The Day After Tomorrow," the Pentagon commissioned a $100,000 study of abrupt cooling scenarios, triggered by a similar stagnation of the oceans.

The authors envisioned "a world of warring states" and "a significant drop in the human carrying capacity of the earth," a future so bleak it could haunt even Hollywood. Partin also finds that a break in the ocean's circulatory system could drop much of Asia into a famine-inducing drought.

But are we heading for this doom? "That's the billion dollar question. Just how probable is this? Well, it's definitely not zero," said Partin. "Right now we have pretty strong evidence that the Greenland ice is not only melting but accelerating."

Greenland is coated in nearly 700,000 square miles of ice, and scientists already know that this ice cover is thinning and that the planet's thermostat is being pushed up by man-made carbon emissions. In 2007 alone, according to a recent study, Greenland lost "the equivalent of two times all the ice in the Alps."

In another new study, published in the journal Geophysical Research Letters, three scientists from Germany's Alfred Wegener Institute looked at the effect of this melting. Not only did they find evidence of an effect, they concluded that existing models may have underestimated the sensitivity of the ocean's system.

Even a relatively small change in the ocean's salinity, the researchers write, "corresponds to a significant temperature decrease of up to 40%" across North America and Europe.

That doesn't surprise Joshua Willis, an oceanographer at NASA's Jet Propulsion Laboratory, who was not involved in the latest studies. "In a lot of areas of climate change, we're seeing that earlier estimates were conservative," he told MSNBC.

He's the lead investigator of a five-year, $30 million study that should help scientists determine Greenland's melt-rate with unprecedented accuracy. The official NASA "mission" is known as Oceans Melting Greenland—yes, it's called operation OMG.

But Willis isn't ready to panic, let alone call Dennis Quaid. "It's not going to be the 'Day after Tomorrow,'" he said. "Impacts like that are way overstated."

Still, both he and Partin share a hope that the world leaders will rein in greenhouse gas emissions, and soon.

"The longer we wait," said Partin, "the longer it will take for us to get back to normal."