Nexus - 1002 - New Times Magazine-pages

Page Content (OCR)

volume of 75 Amazon Rivers. It car- ries heat absorbed in the tropics, and moves up the East Coast of the United States, then northeastward toward Europe. When the Gulf Stream's warm, salty waters reach colder latitudes, they give up their heat to the atmosphere. The atmosphere in the North Atlantic region warms by as much as 10 degrees Fahrenheit. Prevailing winds carry the heat eastward into Europe. That's one reason why London, England—which is located at the same latitude as Calgary and Edmonton, Warm surface currents Cold deep currents Canada—has warmer winters than A schematic of the ocean circulation system, often called the Great Ocean Conveyor, that transports heat New York, which is hundreds of miles throughout the world's oceans. Red arrows indicate warm surface currents. Blue arrows indicate cold farther south. deep currents. (Illustration by Jack Cook, WHOI; see webpage http://www.whoi.edu/home/about/ When the Gulf Stream's waters reach whatsnew_abruptclimate.html for colour illustration and animation.) the Labrador, Greenland and other warmer. The atmosphere above the ocean shifts, too. El Nifio northern seas and lose their heat to the atmosphere, they rearranges worldwide wind and rainfall patterns, causing become colder and hence denser. The waters are also relatively destructive droughts, floods, storms and forest fires. Not to salty. Salty water is denser than fresher water, so the whole downplay El Nifio in the least, because it causes grave human salty mass begins to sink to great depths. suffering and billions of dollars in damage, but El Nifio is When this sinking mass of cold water reaches the Abyss, it relatively short-lived. It lasts only a year or two. then flows at deep levels of the ocean, from the North Atlantic The climate changes I'm concerned about last longer and southward into the South Atlantic. involve the ocean circulation system that spans the entire The plunge of this great volume of cold, salty water propels globe—a system which we often call the Great Ocean the Great Ocean Conveyor. And on the back end, it creates a Conveyor. void that actively pulls the Gulf Stream northward to replace The Great Ocean Conveyor is the ocean's major heat- the waters that are sinking. circulating system. The ocean keeps our planet from It's a pretty neat system. We have been operating under the overheating by transporting heat north and south, from the climate conditions created by this beneficent oceanic heating, equator to the poles, in currents travelling near the ocean ventilation and cooling system for centuries. surface. In the Atlantic, the Conveyor removes heat from the But what if this system weren't operating today? What if Southern Hemisphere and releases it to the Northern cold North Atlantic waters didn't sink and warm equatorial Hemisphere. waters weren't drawn in to replace the sinking waters? Then The most famous and most important of these currents is the — the North Atlantic region would be a much different, much Gulf Stream. The vast Gulf Stream transports the equivalent colder place. Sinking cold salty water : Warm sally water The Great Ocean Conveyor is propelled by the sinking of cold salty (and therefore denser) waters in _Ice sheets reveal annual layers, which scientists the North Atlantic Ocean (blue arrows). That creates a void that pulls warm salty Gulf Stream waters can analyse to reconstruct the history of precipi- northward (red arrows). The Gulf Stream gives up its heat to the atmosphere above the North Atlantic tation and air temperatures 100,000 years in the Ocean, and prevailing winds (large red arrows) carry the heat eastward to warm Europe. (Illustration past. (Photo by Lonnie Thompson, Ohio State by Jack Cook, WHOI; see WHO! website for animation.) University) Ice sheets reveal annual layers, which scientists can analyse to reconstruct the history of precipi- tation and air temperatures 100,000 years in the past. (Photo by Lonnie Thompson, Ohio State University) 12 = NEXUS www.nexusmagazine.com FEBRUARY — MARCH 2003