Maybe Itís Cold Outside

As strange as it sounds, the global warming the world is now experiencing could have a strange consequence in North America and in Europe. It could make things pretty darned cold! I know that seems backward, but let me explain.

Unlike Venus, which has a runaway greenhouse climate and is really hot as a consequence, Earth has a climate that is largely a self-correcting mechanism composed of many parts. When one part gets out of kilter, others respond to counter it. In this case, the atmosphere has been warming for some time and continues to do so today. While most of us think that the obvious response should be ever warmer temperatures everywhere, it might not actually happen that way for places around the North Atlantic Ocean.

The Great Ocean Conveyor, particularly the Gulf Stream portion of it, is the key to this puzzle. The Great Ocean Conveyor is the vast oceanic circulation of heat in the waters of the Atlantic Ocean. It flows because cold, salty water in the North Atlantic sinks and warm, salty water from the Gulf Stream is pulled northward to replace it on the surface of the ocean.

The Gulf Stream is a huge warm water current that transports heat away from the tropics into the Northern Hemisphere. With a volume equivalent to 75 Amazon Rivers, this massive current flows north along the American and Canadian east coasts. In doing so, it transports tropical heat along the eastern seaboard of the North America and then to the North Atlantic Ocean. It is so effective, it warms the air over the North Atlantic by as much as 10 Fahrenheit degrees.

The prevailing westerly winds then carry the heated air over Europe and strongly moderates the climate there as a result. As an example, stunted palm trees actually survive on Scotlandís western coast! Carried by the current, coconuts washed ashore and took root in a place that should be too cold for them to survive but is not because of the Gulf Stream that brought them there. Thanks to the Gulf Stream, London, at about the same latitude as Calgary, Canada, has much milder winters than New York City, which is several hundred miles farther south.

Back into the water now. When the Gulf Stream reaches the North Atlantic, it surrenders the heat it carried, becomes cold, and sinks to the bottom of the ocean. It then travels southward to begin the Great Conveyor route once again. Sounds great, doesnít it? Scientists used to think that this mechanism has been in place all along and would continue to flow indefinitely. Thatís just not so in either case.

Research over the last 20 years has proven that the Gulf Stream and the whole Great Ocean Conveyor system has actually stopped many times in the past. Ice and ocean sediment cores taken all over the planet have been used to reconstruct the climate history for the past 100,000 years and more. Among other examples, scientists found that about 12,800 years ago (the Younger Dryas period), the North Atlantic Ocean cooled dramatically and so did the landmasses around it.

They linked the colder period to a time when the warm water stopped flowing northward. About 1,000 years ago, the Norse were able to colonize Greenland and planted vineyards that prospered there, but these settlements disappeared about 500 years ago when the climate turned cold again. Evidence points to the shutdown to the Gulf Stream as the culprit for the abrupt change.

Over and over again, long-term cold snaps have appeared in the ice and ocean sediment records. During the Little Ice Age, northern Europe was much colder than it is today. Winters were severe and glaciers moved down the slopes of the Alps. In the mid 1700s, abrupt cooling caused famine in western Europe, especially in Ireland and France, where farmers depended on wheat and potatoes. In that same era, a Flemish painter, Bruegel, did his famous frozen landscapes that would not be possible today because the canals he painted no longer freeze.

During the American Revolutionary War, Washington made a dramatic crossing of an ice-bound Delaware River, dragged cannon across icy ground to save Boston from destruction by the British, and suffered tremendous manpower losses at Valley Forge in severe winter cold. None of these would have occurred without the disappearance of the Gulf Stream. How different would history be if the Gulf Stream had flowed normally back then?

Clearly, the Great Ocean Conveyor flow is vitally important to us, so what causes it to stop? Evidence strongly suggests that global warming is the culprit. Hereís why. As atmospheric temperatures rise, ice melts and the water drains down rivers into the sea or in the case of polar ice, crashes directly into the oceans. Remember the ice sheets that have broken off the Antarctic Ice Shelf in the last few years? That ice represents a tremendous amount of fresh water that is suddenly forced into the sea.

Between the glacier melt and the ice sheets that dump into the ocean, there is an awful lot of fresh water being introduced into the Great Ocean Conveyor. That is a problem because fresh water is lighter and less dense than salt water. If there is too much fresh water in the North Atlantic, it will not sink and the vast circulation grinds to a stop. The winters on both sides of the North Atlantic Ocean get significantly colder.

The ocean can handle some additional fresh water in the system but there are limits and the flow slows as the limit is approached. Unfortunately, since the 1970s and especially in the 1990s, incredible amounts of fresh water have already been absorbed and the flow of the Great Ocean Conveyor is slowing. According to scientists at Woods Hole Oceanographic Institute and at the British Centre for Environment, Fisheries, and Aquaculture Science, it is currently flowing 20 percent slower than it did in the 1970s, a period when slowing was already in evidence.

While no one knows at what point the flow just stops, many scientists are sure of the surprisingly rapid results when it does. Transitions from warm to cold occur in only 3-10 years and ensuing cold periods last 500 to 1,000 years before the system corrects itself and the flow resumes. Where the effect is most felt, in eastern North America and in northern Europe, winters are harsh and long, summers cooler and, in some places, drier. The cool-down could be dramatic.

Average winter temperatures could drop 5 Fahrenheit degrees over most of the United States and drop 10 Fahrenheit degrees over eastern Canada, the Northeast US, and in Europe. Yeow! Considering over 60 percent of the world economy is based in the regions most affected, this could create very serious problems for every human being on the planet.

Violent weather swings, crop failures, famine and war could all wait just around the corner if a cold period occurs. Rivers and harbors that freeze over could choke the transport of goods as would weather disruptions in ground and air transport systems. Energy demands could soar and agriculture and fisheries will require dramatic changes to survive.

The world population is over 6 billion today. In previous cold periods, the population was much smaller and much of the world was uninhabited so there was room for mass migrations. There is no such room available today.

That said, nobody really knows what will happen in the future. Maybe the Great Ocean Conveyor will stop and maybe not. The only way we are going to know is to wait and see. Like any good Boy Scout, however, we should always be prepared.

Things could get pretty serious if we do not prepare for the worst and be ready to adapt to change. It is possible, of course. Our ancestors managed it with far less technology than we have today. Understanding how things happen is the first step in a long walk into the future. Are we ready to keep walking? We need to be ready because maybe itís cold outside!

Written by Melody L. Higdon, 14 WS/DOPA

November 2002