Question

Mr Morrison, tell me about the great ocean conveyor belt, I heard it in a few years will bring a new ice age, what are the risks, this is true?

Sunlight falls preferentially near the Earth’s equator. Atmospheric and ocean circulation redistributes the energy, carrying it from low latitudes to high latitudes. For millions of years there has been a fairly steady system of ocean currents that are sometimes called the “ocean conveyer belt”, in which water heated by the Sun at low latitudes flows along the surface of the ocean toward the poles, where it cools and sinks, returning to the equator at great depth. The best known part of the system is the Atlantic Gulf Stream, which flows north through the Atlantic, warming parts of North America and Europe, before cooling in the Arctic. Scientists have mapped the currents, but there are many uncertainties about how stable they are. The buoyancy of the water is influenced by both its temperature and its salt content (salinity). The concern is that as the fresh-water ice in the Greenland icecap melts, this will reduce the salinity of the ocean near Greenland and might disrupt the conveyor belt. There is no doubt that the Greenland ice is melting rapidly. I was just in Greenland, and the rapid retreat of the glaciers is truly dramatic. There is also a theory that the period of northern-hemisphere cooling 12,000 years ago (called the Younger Dryas) took place when a inland sea of fresh water covering much of Canada was suddenly released into the North Atlantic through the St Lawrence River, effectively shutting off the conveyor. This would not cause a global ice age, but the cooling would destroy much of the agriculture in Europe and Canada. No one knows how likely this is, but certainly we would not want to see this happen.

David Morrison
NAI Senior Scientist
July 27, 2009