n Roland Emmerich's The Day After Tomorrow, audiences are treated to some of the finest special effects any disaster movie has ever seen as the Earth's climate spins out of control, flooding and then freezing the city of New York while a new ice age settles over the globe. Why? Why else? Global warming!
Is this patent nonsense? Can global warming cause global freezing? The short answer is, to quote Buckaroo Banzai, "Yes on 1, no on 2," with a couple of qualifiers. Earth is a self-regulating environment, whose response to heat and cold is complex and occasionally counterintuitive. Global warming can't freeze the Earth, but it can change the distribution of temperature and rainfall, with surprising results. For this reason, the term "climate change" has largely replaced global warming as the watchword of environmental activists.
Unfortunately, this implies that an unchanging climate is normal, which it surely is not. Nor can we reliably predict the effects that a given climate change will have. But we'll come back to this point in a minute.
Most readers here are, I'm sure, familiar with the Gulf Stream, which takes warm water from the Gulf of Mexico and carries it north along the U.S. Atlantic coast, then east to Ireland and Britain and Scandinavia, making certain coastal areas several degrees warmer than they otherwise would be. This affects cloud and storm formation and therefore softens inland climates as well. In Cornwall, in the extreme southwest of Britain, it's actually possible to grow palm trees even though the area is farther north on the globe than the chilly Canadian city of Winnipeg!
Staying current
What drives this current? Well, it's actually part of a larger system called the Atlantic Conveyor, powered by the simple fact that cold water is denser and heavier than warm water. Thus, cold water in the polar regions tends to sink, drawing warm water in on top of it. Where the Gulf Stream dead-ends in the North Atlantic, a stream of arctic water dives under it, forming a southward current running along the bottom of the central Atlantic. This current then continues all the way around the horn of Africa, joining the global conveyor system of the Indian and Pacific oceans.
The problem? In Emmerich's what-if scenario, the rise of global temperatures melts the ice sheets of Greenland and the North Pole, pouring billions of tons of fresh water into the North Atlantic. Unfortunately, fresh water is lighter than salt water, and refuses to sink even when it's cold. Thus, a sudden melting would literally put a lid on the salty ocean, preventing it from circulating properly. No Atlantic Conveyor. No Gulf Stream. No date palms in Penzance.
Is this possible? Sure. There's good evidence that a similar scenario played out several times during the past 100,000 years, with significant climatic effects. Could it happen suddenly? Well, yeah, maybe, if "suddenly" means a period of 10 or 20 years, and "it" means a partial (never total) shutdown of the Gulf Stream. Think of the current as a really, really, really heavy truck; it has an unthinkable momentum behind it, and an engine that never quite shuts off. But could this cause a new ice age? Um, no. Not really. To do that you'd need to cool off the entire world, or at least the entire Northern Hemisphere, by about 3 degrees Celsius, and fortunately that's the exact opposite of what we're seeing right now on the global thermometer.
The exact effects of an Atlantic Conveyor shutdown are as hard to predict as next month's weather, but the basic gist is so painfully simple that even Hollywood could understand it. Because, like, if it's warm enough to melt Greenland at a latitude of 60-80 degrees, it's also much too warm to freeze Manhattan at the comparatively tropical 41st parallel, or even Oslo, Norway, which is about even with Greenland's southern tip. As crazy as it sounds, global warming makes the globe warmer, not colder.
Basically, the regions robbed of the Gulf Stream would see colder oceans and warmer air. Less rain, more sun. This would certainly have an effect on the local weather and agriculture, but even in the very worst imaginable case, Europe would be warmer and wetter than central Canada is today. Maybe a lot warmer, and that's the real problem.
Or is it? In "Global Warming, Hurrah!" (January 2000) I argued that the benefits of a warmer world seem to outweigh the perils, and especially the grim prospect of global cooling, which would lock up more and more of Earth's water as ice, resulting in larger deserts as well as glaciers and polar caps. Still, the Earth's climate seems to jump from one stable point to the next, and those sudden (i.e., decades-long) transitions promise to be difficult and painful—perhaps even calamitous—to societies caught in the wrong place. A great many reputable scientists have argued that if the system is poorly understood and its tipping points are unknown, we should avoid perturbing it with our pollution.
Making more technology, not less
Well, I'm not a reputable scientist, but a disreputable science-fiction hack with a long track record of crazy ideas, and I say phooey to that, because climate change is all around us, all the time. Human contributions such as greenhouse gas can be controlled to some extent, with considerable economic fallout, but we are by no means the only variable in the system. We're not even the largest. In fact, I suspect we're sixth on the list, after the waxing and waning of our inconstant sun, the chaotic orbit of our planet, the eruption of huge volcanoes, the release of trapped methane from the ocean floor and the passage of cosmic dust clouds between the Earth and sun.
Like planetary bouts of flu and scarlet fever, these events happen outside our control, and if the environmental crowd is serious about wanting a completely stable climate, then we had better figure out ways to warm the globe rapidly when nature cools it off. Rapid cooling is easy by comparison: Simply block out the sun with smoke, dust, orbiting parasols, or whatever else may be handy. As with most other problems, the answer I see is not less technology, but more. Lots more! Let's build a global thermostat and regulate it to suit our whim. If that's not good enough—if the Green lobby is truly serious about letting nature take its course, come what may—then properly speaking they should all refuse medical treatment and die at the age of 35. I hope they don't, but Lord knows there's no law against it.
On a final note, let's examine those scenes of human beings flash-frozen in their tracks, like unwilling statues. Since human body temperature is 37 degrees Celsius, and the average human body is basically a 70-kilogram sack of fatty saline, and one calorie of heat changes the temperature of 1 gram of water by 1 degree, it would take an instantaneous loss of 2.6 million calories to cool a body to freezing temperature. Actually freezing it solid requires additional energy, called the "latent heat of fusion," amounting to another 5.6 million calories. According to my calculations, for the air to carry away this much heat in one second it would need to be just above the temperature of liquid nitrogen (-196 C), and moving at a biting 45 kilometers per second. This ignores the effects of friction and supersonic compression, which are considerable at those speeds, so suffice it to say no weather on Earth could ever do this to a person.
Which is not to say the movie isn't fun, if you remember to park your brain at home. Or better yet, bring it with you and try to estimate just how improbable the story really is. If nothing else, this silly movie has got people reading and talking and thinking about these issues, which is the first step toward sensible planning. Now all we need is that thermostat. ...
Wil McCarthy is a rocket guidance engineer, robot designer, nanotechnologist, science-fiction author and occasional aquanaut. He has contributed to three interplanetary spacecraft, five communication and weather satellites, a line of landmine-clearing robots and some other "really cool stuff" he can't tell us about. His short writings have graced the pages of Analog, Asimov's, Wired, Nature and other major publications, and his book-length works include the New York Times notable Bloom, Amazon's "Best of Y2K" The Collapsium and, most recently, Lost in Transmission. His acclaimed nonfiction book, Hacking Matter, is now available in paperback.
