El Niño
El Niño is a periodic shift in weather and ocean currents. It is more formally known as El Niño Southern Oscillation or ENSO.
El Niño events affect global weather conditions, changing rainfall patterns and storm intensity. Satellite image of hurricane Katrina, 28 August 2005, courtesy NOAA
El Niño Conditions
During El Niño conditions, the trade winds weaken, causing Pacific Ocean currents to change. The shift in ocean currents allows warm water from the western Pacific to flow toward the east. Changes in ocean currents also affect global weather conditions, changing the distribution of rainfall and storms, which can cause both severe droughts and floods.
El Niño and Coral Bleaching
El Niño events bring unusually warm water to many coral reefs worldwide. Mass bleaching on coral reefs around the world occurred during ENSO events in 1983, 1992, 1995, 1998, 2000, and 2002 (a minor ENSO year, but the most extensive bleaching event on the Great Barrier Reef).
Severe bleaching lowers the corals’ reproductive output for a year or more while they recover. More frequent and intensive ENSO events may suppress the ability of corals to recover at all from mass bleaching.
One possible side effect of rising global temperatures might be more frequent and intense El Niño events.
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