Tuesday, October 13, 2015

ANS -- We’re closer to a ‘Day After Tomorrow’ ice age than we thought

Here is a short article that's an update on the scientific feasibility of the scenario shown in a movie.  Turns out it's feasible after all, though a bit less dramatically.  

We're closer to a 'Day After Tomorrow' ice age than we thought


Updated with correction below.

A collapse of the Atlantic meridional overtunring circulation could increase water levels in mid-Atlantic cities by 0.5 to 1 meter. (Joe Raedle/Getty Images)

The oceans crash against skyscrapers, making aquatic tunnels of Manhattan streets. Heavy layers of snow pile on endlessly, burying entire civilizations in canopies of white. Eventually, liquid turns to ice, and life as we know it is threatened by an eternal freeze.

This is the harrowing disaster scenario of "The Day After Tomorrow," a 2004 science fiction film directed by Roland Emmerich and starring Jake Gyllenhaal. Based on an imagined future of accelerated global warming, the movie was a major box office hit — it grossed over $500 million worldwide — but climatologists quickly took aim at its scientific value.

Patrick J. Michaels, a noted climate change skeptic, wrote in USA Today after the film's release, "As a scientist, I bristle when lies dressed up as 'science' are used to influence political discourse. … Each one of these phenomena is physically impossible."

He joined a chorus of critics who deemed the film wildly counterfactual. Yahoo featured "The Day After Tomorrow" in a top 10 list of scientifically inaccurate movies, while Duke University paleoclimatologist William Hydedeclared, "This movie is to climate science as Frankenstein is to heart transplant surgery."

The extreme cooling trends depicted are caused by a collapse of the Atlantic Meridional Overturning Circulation, or AMOC, a North Atlantic ocean water circulation system that moderates temperatures north of the equator. When the movie was released, however, there had yet to be research examining such an event's potential aftermath.

Now, a University of Southampton climate study published in Nature Scientific Reports indicates that we were naive to feel safe from "The Day After Tomorrow"-esque realities.

"The basic scenario of the AMOC as a result of global warming is not completely out of the blue or unthinkable," the study's author, Sybren Drijfhout, told The Washington Post.

[Why some scientists are worried about a surprisingly cold 'blob' in the North Atlantic Ocean]

According to the oceanography and climate physics professor, current warming patterns not only indicate that a collapse of the AMOC is possible, but also that resulting consequences would resemble "The Day After Tomorrow," though not to the same extremes.

Using an advanced climate model at Germany's Max-Planck Institute to simulate both conditions of global warming and conditions of an AMOC collapse, Drijfhout's team discovered that global temperatures could register a drop of up to 20 degrees Fahrenheit — three times stronger than concurrent warming trends.

The cold of a "Little Ice Age" would hit Western Europe the hardest, as indicated by this heat map. (Sybren Drijfhout)The cold of a "Little Ice Age" would hit Western Europe the hardest, as indicated by this heat map of 15 years after the start of AMOC collapse. (Sybren Drijfhout)

In a properly functioning circulatory system, the AMOC produces a milder climate downstream of the North Atlantic by bringing warm, salty surface water from the Indian Ocean and the South Atlantic to the northern hemisphere.

But this system depends on the connection of surface waters flowing to the north and deeper waters flowing to the south — imagine a "global conveyor belt" — that can occur within just a few sinking ranges in the North Atlantic. These ranges exist only where water on the surface sufficiently nears the freezing point such that it becomes dense and heavy enough to sink to the bottom.

(For further explanation of the process, click here.)

With the Greenland ice sheet melting as a result of climate change, the AMOC's essential process is slowing down. If we're not careful, Drijfhout said, it may produce an effect comparable to "The Day After Tomorrow."

While the climate sequence in the movie is certainly sped up and exaggerated, scientist noted, the real-life consequences of an AMOC collapse would be no less cause for worry.

The cold would hit Western Europe the hardest, while Americans would have to contend with floods. The United Kingdom, the Netherlands and Denmark would likely to experience 5-degree temperature drops; sea levels on the U.S. East Coast could could rise more than three feet.

"This would affect hundreds of millions of people," Drijfhout said, "At least temporarily, Europe would suffer conditions that would look like the Little Ice Age of the Middle Ages."

The collapse of the AMOC would be accompanied by a continuation of global warming conditions. These would ultimately offset and overtake the cooling trends in about 40 years, though in some places near the eastern boundary of the North Atlantic, the reversal could take more than a century.

Near the end of "The Day After Tomorrow," the heroes reach a library buried in snow, its occupants surviving just barely on the heat of burned books. New York has become a subarctic city, and helicopters scan its frozen landscape, looking for survivors.

Perhaps most tragically, it was all forecast in the beginning by the main character, a paleoclimatologist whose warnings fell on deaf ears.

"When it comes to climate change," Drijfhout said, "we are playing a dangerous game."

Correction: A previous version of this article incorrectly stated the temperature drops that would occur as a result of an AMOC collapse.

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