Why are the Coral Reefs in the Oceans becoming bleached?

Could it be the weather, the water, or us?

Coral reef bleaching occurs when water temperatures exceed the maximum range that corals can tolerate.  Corals typically grow in warm tropical waters between 70-85 degrees Fahrenheit. When sea surface temperatures rise or other stresses occur,the corals expel the symbiotic algae that gives them color. This phenomenon is referred to as coral bleaching.

Prior to the 1980’s, most bleaching events reported attributed to localized phenomena such as major storm events, severe tidal exposures, sedimentation, rapid salinity changes, pollution, or thermal shock. Since 1980, however, bleaching events have not been so easily explained. Research has shown a direct relationship between bleaching and water temperature stress. Extreme water temperatures have been implicated in the majority of the major bleaching events of the 1980s and 1990s.