The Day After Tomorrow
Dennis Quaid, Jake Gyllenhaal
Premise: When the world’s ocean circulation patterns are disrupted by melt water due to global warming, the Earth is plunged into a sudden ice age.
There’s a fair amount of good in this movie, and a fair amount of hoo-hah as well. I’ll focus on the Earth Science problems that I have at least a little expertice in. I’m not a meteorologist, so I can’t say a lot about the huge storms that play an enormous role in the movie (though I suspect they fall into the category or hoo-hah).
Ice core drilling: This is, in fact, a common means by which we have learned a great deal about Earth’s past climate. And we can go back ten thousand years quite easily. The ice-coring set-up that they have is quite unlike any I’ve ever seen, and I really don’t think any intelligent scientist would be coring on an ice shelf, but for the sake of a movie… ok.
A two-century long ice age that started 10,000 years ago: There was a substantial climate change that occurred ten thousand years ago. It was warming, though, not an ice age that lasted 200 years. This was about the time that humans found themselves in North America and was also about the same time that all the cool ‘megafauna’ went extinct (like mammoths, mastodons, woolly rhinos, ground sloths, etc.) There is a great deal of debate over whether it was the appearance of humans or this climate change that did in the megafauna.
Greenhouse gasses from ice cores: This is actually a commonly used research track by paleoclimatologists. In fact, we have two such scientists in our tiny department here at the University of Rochester. Atmospheric gasses are trapped in snow which is later buried and turns to ice in the massive glacial sheets of the Arctic and Antarctic. These gasses can be retrieved and studied, providing information about past concentrations of greenhouse gasses in the atmosphere.
By the way, we can assign ages to different parts of ice cores by simply counting annual rings. During the winter, snow tends to be clean, but in the summer there tends to be a lot of dust in the snow. Each year, then, there is a layer of clean ice and dirty ice in an ice core. We can count these (like tree rings) to know the age of a part of an ice core. Pretty cool, eh?
Ocean circulations: What the main character says about the disruption of ocean currents by the introduction of fresh water (from melting ice sheets), which then leads to climate change is actually an accepted hypothesis. It has been put forward by Wally Broeker, one of the most respected paleooceanographers in the world.
Unfortunately, the movie does make a mistake here. Not a severe one, but I’m sure Wally himself would facepalm. They talk about the North Atlantic Current – which is a real thing – being shut down by all the meltwater. The North Atlantic Current is a surface current in the ocean. It is the continuation of the Gulf Stream, which runs north along the eastern margin of North America. The Gulf Stream plus the North Atlantic current is what keeps the climate of Europe so pleasant despite being so far to the North. Surface currents, like the North Atlantic Current, are driven by wind.
If you look at the drawings that the main character of the film is referring to, as well as Wally Broeker’s work, you’ll realize that the currents that would be disrupted by the freshwater are not surface currents at all. While it might affect the North Atlantic Current, the influx of meltwater would more likely disrupt the deep ocean currents, called “Thermohaline Circulation.” These currents are driven by differences in temperature (Thermo-) and salt-content (haline) of the water. Saltier water sinks, as does colder water. This global circulation keeps the ocean water mixed from north to south and from ocean to ocean. An influx of freshwater from melting glaciers in the north and south would stop the downwelling in those areas, which would disrupt this circulation. This, it is widely accepted, could have a profound effect on global climate.
Water inundating New York City: This is a head-scratcher. Sure, if sea-level rises, then water could rush into the city. And now, post Hurricane Sandy, we know that water can make it quite a ways into the city. There is a lot of water tied up in the world’s ice sheets, too, so an immense sea level rise is not out of the question if we melted all of the ice. But the converse is true, too. In an ice age, sea level can drop because all the Earth’s water is tied up in ice sheets at the poles. Somehow, I suspect that these two competing phenomena would have prevented the great wall of water that struck New York in the movie. But it was pretty cool to have a massive ship floating in front of the library, eh?
Only storms in the Northern Hemisphere: Was anyone bothered by this? Why wouldn’t there be enormous storms in the Southern Hemisphere too? How come Australia gets out Scot-free? This actually might not be that big of a problem. It seems that the great ice ages did not affect the Southern Hemisphere in the same way as the Northern Hemisphere. There were no huge ice sheets in the south. Part of this is because there really isn’t much land mass in the south. There are some tall mountains that even now have glaciers that may have expanded during the northern ice ages, but it seems that “ice ages” as we think of them were a primarily northern phenomenon. There’s active research on that topic going on right now. So it’s possible that a new ice age might only affect the Northern Hemisphere.
An ice age in a week? I think this is fundamentally the biggest problem with “The Day After Tomorrow.” The premise is ok, and the idea that run-away greenhouse gasses could cause major climate disruptions isn’t that far off, but that an ice age can begin and coat much of the Northern Hemisphere in ice in less than a week is a unlikely. Years is a better scenario, and we’d probably have a little warning. Can can observe the flow of the thermohaline currents. We’d see them stopping most likely. Alas, I don’t think that there’s a thing in the world we could do to re-start the flow should it stop. Climatic disruption is the most likely outcome.