Scientists have many theories to explain what is going on, such as global warming caused by the greenhouse effect and human pollution. But most prefer to attribute it to natural variations in currents and wind patterns rather than a fundamental shift in worldwide climate. Starting last fall, Lynn said, his agency began measuring above-normal temperatures along the West Coast. The temperature is now about 62.5 degrees off San Francisco, about 3 degrees higher than usual during this time of year. Although his agency keeps detailed track of temperatures only in U.S. coastal waters, Lynn said data indicates that the warming goes as far north as the panhandle of Alaska and south along Mexico's Baja California.
Fish already seem to be moving.
Sardines, which nearly disappeared from the West Coast in the 1940s after a drop in water temperature, are returning. Other fish found more commonly in Mexican waters, such as Yellowfin tuna and bonito, are moving into Southern California. The Coho salmon are suffering severely,' said Alec MacCall, director of the Tiburon Laboratory of the National Marine Fisheries Service. Cohos, which spawn in California's coastal streams, may withdraw to the Pacific Northwest or even all the way to Alaska, he said, if the warming continues. Overall, fish catches would probably decline if the water stays warm, because most of the biological productivity of the oceans depends on cold, nutrient-rich waters welling to the surface from deeper layers.