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To track global warming, watch the water flow

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Say "climate change" and people tend to think global warming. But we also should think about water, specifically, the cycle of precipitation, evaporation, and river flow that is a key climate component. A little decline here, a little boost there, can have direct effects on how we live our lives.

In the Arabian Sea, for example, fishermen now enjoy richer fishing thanks to declining snow cover in Southeast Asia and the Himalayas. The links work this way: Less snow means more summer heating of the land, intensifying air pressure differences between land and sea, which in turn drive the seasonal monsoon winds. Stronger winds stir the Arabian Sea more vigorously, bringing more nutrients into its higher, sunlit levels. Microscopic plants and animals (fish food) flourish. Fisheries burgeon.

Arctic inhabitants aren't so fortunate. An intensified water cycle is increasing moisture in the American and Eurasian northlands. Rivers fed by stronger precipitation are pouring more freshwater into the Arctic Ocean. It caps the upward flow of fish food. This is bad for fisheries.

Changes in the water cycle itself may be subtle and often poorly understood. Yet their effects can sometimes be dramatic. Joaquim Goes at the Bigelow Laboratory for Ocean Sciences in West Boothbay Harbor, Maine, and several colleagues studied satellite images of the western Arabian Sea and found sea-color changes due to seasonal blooms of phytoplankton (microscopic plants). In fact, the blooms have increased more than 350 percent in seven years, the research team reported in Science last month.

These robust phytoplankton blooms can enhance fisheries, Dr. Goes says. But too much phytoplankton can deplete the water's oxygen supply. That can kill fish and encourage bacteria that release nitrous oxide, a gas with 310 times the heat-trapping power of carbon dioxide.

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