In 1899, the Indian monsoon failed, leading to drought and famine in India.  This led Gilbert Walker, the head of the Indian Meteorological Service, to search for a way to predict the Indian monsoon.  By the early 20th century, he had identified a peculiar see-saw relationship between pressure over the maritime continent and India and the Pacific near South America.  When pressure is high over the eastern Pacific, it is low over the maritime continent, and vice versa.  He called this relationship the Southern Oscillation.