Climate scientists identified a likely new victim of global warming on Wednesday: the vast looping system of air currents that fuels Pacific trade winds and climate from South America to Indonesia.

This could mean more El Nino-like weather patterns in the United States, more rain in the western Pacific and less nourishment for marine life along the Equator and off the South American coast. Known as the Walker Circulation, this system of currents functions as a huge belt stretching across the tropical Pacific, with dry air moving eastward at high altitude from Asia to South America and moist air flowing westward along the ocean`s surface, pushing the prevailing trade winds.

When the moist air gets to Asia, it triggers massive rains in Indonesia. Then it dries out, rises and starts the cycle again, heading east. This important system has weakened by 3.5 percent over the last 140 years, and the culprit is probably human-induced global warming, scientists reported in the current edition of the journal Nature.

"This is the impact of humans through burning coal, burning benzene, gasoline, everything," said Gabriel Vecchi of the US National Oceanic and Atmospheric Administration and an author of the study. "It`s principally the greenhouse gases from fossil-fuel burning."

The observed slowdown has been more pronounced in the last 50 years, Vecchi said in a telephone interview, noting this fits with what theorists and computer models predict should happen as a result of human-induced global warming. It is not consistent with any natural fluctuation in the system, Vecchi said.

Even this relatively small weakening in the Walker Circulation means a much larger slowing of wind-forced ocean currents, the scientists found. This could spur "El Nino-like" effects, Vecchi said, and these in turn could have an impact as far as the United States, South America and Australia.

While these potential effects are being studied, Vecchi said it could mean more rain in the southern United States, droughts elsewhere in North America, and more rain in Pacific islands like Kiribati. The slowdown in ocean currents is also expected to cut down on bottom-to-top ocean circulation that brings nutrients up to the surface where marine life can feed on them, which could have an impact on fishing in the equatorial Pacific.

The weakening of the Walker Circulation is projected to continue, and could weaken another 10 percent by 2100, the scientists reported. This could mean ocean flow could decrease by close to 20 percent.
(Planet Ark, 04/05/2006)
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