Is Europe about to freeze?

• Position: Climate - Brief Article

One of the odd possibilities that could emerge from global warming is that much of Europe, robbed of the ocean current patterns that help keep it warm, could rather abruptly enter a deep freeze and have a climate that more closely resembles Alaska than the modest temperatures it now enjoys. It is by no means certain that climatic changes of this magnitude and speed will come to pass, scientists say, but even the possibility that they might are a cause for serious concern.

According to Peter Clark, professor of geosciences, Oregon State University, Corvallis, one of the world's leading experts on glaciers and prehistoric climate changes, "What is fairly clear is that, if the ocean circulation patterns that now warm much of the North Atlantic were to slow or stop, the consequences could be quite severe. This might also happen much quicker than many people appreciate. At some point, the questions become how much risk do we want to take?"

The big variable in this particular equation, he says, is whether changes in global temperature and precipitation patterns might affect a gigantic conveyor belt of warm, less-salty surface water that moves from the tropical Atlantic Ocean until it finally becomes so cold and salty in the far North Atlantic that it sinks, moves south, and continues the circulation pattern. This process, called thermohaline circulation, happens in just two regions of the Earth's polar areas. Nevertheless, it is responsible for much ocean circulation, including the critical currents that help keep parts of North America and Europe far warmer than they would otherwise be, considering the far-north latitudes at which they lie. (Most of Great Britain is at the same latitude as central Canada.)

This circulation process, scientists say, is not inevitable. Research suggests it may have fluctuated or even stopped numerous times in Earth's distant past, and that it is especially sensitive to moderate increases in temperature or influxes of fresh water. The same very cold, very salty water that sinks if it is just a little bit less salty. At various times, it appears these changes have happened not in geologic terms of thousands of years, but, rather, decades. "This system does not respond in what we call a linear manner," Clark explains. "Once you start putting on the brakes, this circulation pattern could slow down faster and faster and eventually stop altogether."

Research...