ssure air over the region along the equator suddenly switch places, for no apparent reason, starting a meteorological chain reaction affecting weather around the world. The first impact is seen as Pacific trade winds that usually blow east to west fade and sometimes even reverse, and without these winds, warm tropical water from the South pacific creeps as noted toward South America and raises ocean temperatures near Peru as much as 7 degrees. These warm waters bring with them rain clouds that produce torrential showers in parts of Peru and Chile. This phenomenon may have been encountered by the Spanish conquistador Pizarro, who reported that his way was often blocked by flooded streams during his 1532 invasion of Peru. Indonesia and northern Australia are the usual sites for these rains, and during an El Ni±o they remain bone dry.
The El Ni±o Southern Oscillation--the full name of the phenomena--was noted first in 1891 when Luis Carranza, president of the Lima Geographical Society, pointed out to geographers that there was an extension of a warm current flowing between the ports of Paita and Pacasmayo, the current named El Ni±o by Peruvian sailors. Studies conducted since that time have shown through geomorphological, paleontological, and archaeological studies that El Ni±o-related disasters have been occurring for the past 40,000 years. In this century, there have been three distinct periods of scientific study of the issue. From 1900 to the 1960s, scientific knowledge was developed through the efforts of individuals. From the 1960s to 1982, knowledge came from scientific collaboration supported by national programs. Since 1982, international cooperation among scientists has been the norm. During this century, the effort has moved from a reaction to the consequences of El Ni±o to an attempt to predict El Ni±o and its consequences.
The range of influence of an El Ni±o is extended by the fact that it alters t...