Back in the 1500s... Fishermen along the Pacific coast of northern Peru started noticing changes in fish abundance and species. Millions of dead sea birds washed up on the beaches as their prey -- anchovies -- disappeared. Gatherers of guano (bird dung that's sold for fertilizer) fell on hard times as birds quit depositing nutrient-rich droppings. At the same time, sailors observed changes in coastal currents and rainfall, and farmers noticed torrential rains in the typically arid region.

Since the warming often peaked in December, in the 1890s it was dubbed "El Niño," in honor of a previous December visitor, the infant Jesus. By then a few scientists had become intrigued by the phenomenon. But the vast Pacific yielded its data only grudgingly, and it was hard to know the true extent of the warming -- or indeed even what was "normal" in the Ocean. Interest intensified in the late 1960s and early 1970s, and using new observations including satellite data, climatologists and oceanographers recognized that El Niño was affecting a whole lot more than just the harvests of anchovies and bird dung. Then, during the 1982-83 El Niño, the sea surface west of Peru was as much as 4° C warmer than average during the southern hemisphere summer. It was the largest, most intense El Niño on record, and all hell broke loose, climatically speaking. There were torrential rains in normally arid regions of Peru, and floods in southern California. Fires scorched 3 million hectares (7.5 million acres) of tropical forest in Borneo. An estimated 2,000 people died. The damage estimates ranged from $8-billion to $13-billion, including $2.5 billion for disastrous crops caused by drought in Australia, and $2.2 billion to flooding in the United States. Over the succeeding years, scientists studied more El Niños, and linked the warm water, statistically, to increased rainfall in the Southeast United States, and to droughts in Indonesia, Australia, Ethiopia and Zimbabwe. (Indeed, during 26 El Niños, droughts struck Zimbabwe 22 times.) The El Niño also seemed to reduce hurricanes in the Atlantic, while increasing them in the Eastern Pacific. If that isn't a global reach, what is? That was then. Wazz-ahp up now? Two questions loom as the last El Niño has burned out and the next La Niña is firmly established (and maybe ending?). What is the relation, if any, between the apparent increasing frequency of El Niños and the rise in global temperatures we know as global warming? And what can we do to reduce the harm caused by the giant hot water bottle in the eastern Pacific -- or even to take advantage of it? Nice questions. But the quiz is later. First we need to understand the "why" of El Niño.