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CAN GLOBAL WARMING CAUSE AN Ice AGE? CAN GLOBAL WARMING CAUSE AGE? ICE Changes to the ocean currents due to an influx of fresh water could have drastic, abrupt effects on the climate, particularly in the Northern Hemisphere regions currently warmed by the Gulf Stream. ver the past two decades, we have heard about greenhouse gases and the idea that our planet is gradually warming. I'd like to throw a curveball into that thinking—specifically the "gradually warming" part. This new think- ing is little known and scarcely appreciated by policymakers and world and business leaders—and even by the wider community of natural and social scientists. But evidence from several sources has amassed and coalesced over the past 10 to 15 years. It points to a completely different—almost counterintuitive—scenario. Global warming could actually lead to a big chill in some parts of the world. If the atmosphere continues to warm, it could soon trigger a dramatic and abrupt cooling throughout the North Atlantic region—where, not incidentally, some 60 per cent of the world's economy is based. When I say "dramatic", I mean that average winter temperatures could drop by five degrees Fahrenheit over much of the United States, and by 10 degrees in the northeastern United States and in Europe. That's enough to send mountain glaciers advancing down from the Alps...to freeze rivers and harbours and bind North Atlantic shipping lanes in ice...to disrupt the operation of ground and air transportation...to cause energy needs to soar exponentially...to force wholesale changes in agricultural practices and fisheries...to change the way we feed our populations. In short, the world—and the world economy—would be drastically different. And when I say "abrupt", I mean that these changes could happen within a decade and they could persist for hundreds of years. You could see the changes in your life- time, and your grandchildren's grandchildren will still be confronting them. And when I say "soon", I mean that in just the past year we have seen ominous signs that we may be headed toward a potentially dangerous threshold. If we cross it, Earth's climate could switch gears and jump very rapidly—not gradually—into a completely different mode of operation. This is not something new under the Sun. It has happened throughout Earth's history, and it could happen again. THE OCEAN CIRCULATION SYSTEM The key to these climate shifts is that Earth's climate is created and maintained by a dynamic system of moving, interacting parts. Earth's climate system has two main components. The first one you are all familiar with by watching your local TV meteo- rologist or The Weather Channel. It is the atmosphere, which circulates heat and moisture around the globe. But, in fact, the atmosphere redistributes only about half of the energy that the Earth receives from the Sun. The other half is transported around our planet by a circulation system that is equally important, but far less under- stood: the ocean. The ocean isn't a stagnant bathtub. It circulates heat around the planet like the heating and cooling system in your house. The atmosphere and oceans are equal partners in creating Earth's climate. The atmosphere is a rabbit. It moves quickly. Rapid changes in atmospheric circu- lation cause storms, cold spells or heat waves that play out over several days. The ocean, on the other hand, is a turtle. It may take years or decades or even millennia for similar "disturbances" to circulate through the ocean. But the ocean is a big turtle. It stores about 1,000 times more heat than the atmosphere does. So changes in ocean circulation can set the stage for large-scale, long-term climate changes. One example that you may be familiar with is El Nifio. Every few years, oceanic conditions shift and surface water temperatures in the eastern tropical Pacific get by Dr Robert B. Gagosian © 2002 President and Director Woods Hole Oceanographic Institution Woods Hole, Massachusetts 02543 A Email: rgagosian@whoi.edu Webpage: http:/Awww.whoi.edu/home/ about/whatsnew_abruptclimate.html by Dr Robert B. Gagosian © 2002 NEXUS = 11 A TRIGGER FOR ABRUPT CLIMATE CHANGE FEBRUARY — MARCH 2003 www.nexusmagazine.com