Is Cold Part of Our Global Warming?

Creative Commons | RedAndr - self-made, used map from http://www.ngdc.noaa.gov/mgg/image/2minrelief.html

PERSPECTIVES


Op-Ed by PETER MAURER

While in college I took several meteorology classes, based on my roommate’s desire to become a weatherman (which he did). I enjoyed them thoroughly, particularly the opportunities in class when lively conversations would break out.

One of them I still remember vividly, primarily because it eventually was the origin for a Hollywood blockbuster, and also because it may actually be happening in Michigan right now. At the time, although the concept of anthropogenic global warming hadn’t been established, my professor and his colleagues had already witnessed, and were disturbed by, the ever-increasing rate of glacial melt in Greenland.

Although some of the math and peer-review procedures were a mile over my head at that time, I do remember the gist of his concern: trillions of gallons of fresh, cold water entering the ocean may move south, disrupting the warm Gulf Stream and its moderating influence on the winter weather of the British Isles and western Europe.

Normally, the warm waters of the Caribbean flow from the Gulf of Mexico, around Florida, up the East coast of America and then head for England and western Europe. The relatively warm water helps to moderate the winter weather in those regions, resulting in far less severe weather than their latitude would suggest. Look at a map sometime, and you’ll discover that England is lying at the same latitude at southern Hudson Bay in Canada. And none of us has to go that far north into Canada to imagine what their winters are like.

So long as the Gulf Stream continues its gentle ride north and east, Britain and Europe will enjoy relatively mild winters. But if something were to interfere with that conveyor belt of warm water, those same areas would experience brutal winters, ones that would make the Dickens-era winters seem downright balmy.

First, some science.

Ocean water is salty, roughly 3%, and mostly sodium and potassium chlorides. Because of these dissolved salts, salt water is more dense than fresh. During the rainy season, you can take a boat over 20 miles into the ocean off the mouth of the Amazon River and scoop fresh water off the surface of the Atlantic. It takes some time for fresh water to mingle with and become part of the ocean.

As global warming causes Greenland’s glaciers to melt faster-than-normal, more and more cold fresh water is entering the Atlantic and moving south. The Gulf Stream’s warm currents are less dense than the surrounding, colder salt water so they ride nearer the surface. When the cold, fresh, surface water from the glacier melt meet the warm, salty, surface water of the Gulf Stream, it will tend to push the Gulf Stream waters further south. Rather than bathing England and northern western Europe with its warmth, the Gulf Stream instead will influence parts of southern Europe, places like Spain and Portugal.

This scenario, admittedly greatly accelerated and very much ‘Hollywoodized,’ was the idea behind the 2004 movie, “The Day After Tomorrow.” This action movie, however entertaining, served to discredit what a growing number of scientists thought was not only possible, but perhaps happening right under our noses.

This past month, research has unequivocally demonstrated that the Gulf Stream is slowing down, slower, in fact, than at any time in the past 1,600 years. This slowing and subtle shift of the Gulf Stream is also affecting the air pressure systems over the ocean, the North Atlantic Oscillation, which is being tied to colder-than-normal winter and spring weather over the eastern third of North America.

Three of the past five winters in that part of the U.S. have been much colder than normal. Is this a cycle we don’t understand, a one-off perturbation in longitudinal weather data, or the beginning of what some forward-thinking climatologists first saw half a century ago? We should know within a decade.