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Early El Nino. Computer artwork based on satellite data of sea level and temperature in the Pacific in January 1997 during the early part of an El Nino event. North is towards upper left, with the Americas at upper right and Asia at upper left. The three-dimensional sea relief map shows higher sea levels (not to scale) in the west. It was created using NASA TOPEX satellite imagery. Sea temperatures, from NOAA's AVHRR satellite sensor and TAO sea moorings, vary from red (30 degrees celsius) in the west to dark blue (8 degrees celsius). El Nino occurs when a warm tongue of water moves into the eastern Pacific, seriously affecting global weather patterns. (KEYSTONE/SCIENCE PHOTO LIBRARY/NASA)