Does global warming affect sea temperature?

• Position: Oceanography

A North Atlantic Ocean circulation system was weakened considerably in the late 1990s, which could have dramatic effects on climate, maintains a potentially groundbreaking study from NASA. The slowing of this current--which moves water in a counterclockwise pattern from Ireland to eastern Canada--is an indication of changes occurring in the North Atlantic Ocean.

Known as the subpolar gyre, the current has weakened in the past in connection with certain phases of a large-scale atmospheric pressure system known as NAO (North Atlantic Oscillation). NAO has switched phases twice in the 1990s, while the subpolar gyra current has continued to weaken. Whether the trend is part of a natural cycle or the result of other factors related to global warming is unknown.

"It is a signal of large climate variability in the high latitudes," says Sirpa Hakkinen, a researcher at NASA's Goddard Space Flight Center, Greenbelt, Md. "If this trend continues, it could indicate reorganization of the ocean climate system, perhaps with changes in the whole climate system, but we need another good five to 10 years to say something like that is happening."

Adds Peter Rhines, an oceanographer at the University of Washington, Seattle, "The subpolar zone of the Earth is a key site for studying the climate. It's like Grand Central Station there, as many of the major ocean water masses pass through from the Arctic and from warmer latitudes. They are modified in this basin. Computer models have shown the slowing and speeding up of the subpolar gyre can influence the entire ocean circulation system."

Satellite data makes it possible to view...