El Niño events cause fluctuations in temperature and rainfall patterns
in the Pacific basin and beyond. These periodic variations that occur as a
result of the interaction between the ocean and the atmosphere in the tropical
Pacific region can affect ecosystems and human lives in far flung regions of
the globe. This ocean-atmosphere phenomenon, known as the El
Niño/Southern Oscillation (ENSO), affects climate-sensitive human
activities such as agriculture and fisheries. The symbols on this map indicate
the types of impacts associated with "warm" ENSO events, such as occurred
in 1982-83 and during the early 1990s, in which ocean waters in the eastern
tropical Pacific Ocean warm by only one to a few degrees above their normal
conditions. That these relatively small changes cause such significant
responses indicates how sensitive the climate, ecosystems, and society are to
these natural fluctuations. The effects of a La Niña event (an anomalous
cooling of the waters off the coast of South America) also can cause climatic
and ecological disruptions; in some regions, the impact of La Niña is the
opposite of that caused by El Niño. The figure is courtesy of the NOAA
Office of Global Programs.