The link between these climatic effects in distant parts of the globe and El Niño is now well established. Yet it has taken some time for scientists to understand how the various pieces of the puzzle, from ocean currents to winds and heavy rains, fit together. Decades ago, the British scientist Sir Gilbert Walker provided the first clue.
During the 1920s, while scientists in South America were busy documenting the local effects of El Niño, Walker was on assignment in India, trying to find a way to predict the Asian monsoon. As he sorted through world weather records, he discovered a remarkable connection between barometer readings at stations on the eastern and western sides of the Pacific. He noticed that when pressure rises in the east, it usually falls in the west, and vice versa. Walker coined the term Southern Oscillation to dramatize the ups and downs in this east-west seesaw in Southern Pacific barometers.