Rivers run to it

Eurasian rivers dominate the flow of fresh water into the Arctic Ocean. A new hydrology study finds that releases from the six largest of these rivers have increased for some 60 years in near lockstep with steady arctic increases in surface-air temperatures.

Driven by increasing snowmelt and rains, this trend, if it continues, could perturb the northern temperate and arctic climate, argues Bruce J. Peterson of the Marine Biological Laboratory in Woods Hole, Mass., and his colleagues in the Dec. 13, 2002 Science. “It’s a worrisome thing,” he says.

Ordinarily, cold, dense water in the extreme North Atlantic sinks to great depths and flows southward through the Atlantic. Like a hydrologic conveyor belt, this massive flow forces a comparable return of warm surface water into the Arctic.

Ever-larger discharges of fresh water into the Arctic Ocean–as would be expected with continued global warming–could hamper formation of the dense undersea current that drives the conveyor belt. That, in turn, could diminish the return flow of warm water into the Arctic, thereby cooling high northern latitudes, Peterson says.

“It’s a bit of a paradox,” he concedes, “that global warming might cause regional cooling.”

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Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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