Gathering Clues of Past El Ninos

In addition to running truckloads of data through high speed computers, scientists continue to try to figure out what the past looked like by piecing together bits of historical evidence from many different sources, including:

• sea-surface temperature records. Millions of reports from merchant ships crossing the equator have been collected for over a century. Puerto Chicama on the Peru coast has reported water temperature regularly since the 1930s.
• daily observations of atmospheric pressure and rainfall. Some stations, like the one at Darwin, Australia, have records extending back more than 100 years.
• fisheries' records from South America.
• writings of Spanish colonists in settlements along the coasts of Peru and Ecuador dating back to the late fifteenth century.

Another way scientists can make guesses as to what happened in the past is by looking at coral samples and tree rings, which by their annual growth patterns can potentially provide clues to El Niños of past centuries.