Much of the world’s
Coral reefs bleaching faster, more severe than ever, scientists report in study
ocean coral reefs are being destroyed by global warming, and there is little left to do to save them.
Coral reefs are bleaching four to five times as frequently as they did around 1980, scientists said last week in a study that suggests climate change may be happening too rapidly for some reefs to withstand.
“With a fourfold increase over the last 35 years, if you take that forward, it’s unfortunately in complete agreement with what the climate models have been saying,” said Mark Eakin, one of the study’s authors and head of the National Oceanic and Atmospheric Administration’s Coral Reef Watch.
“(We’re) looking at 90 percent of reefs seeing the heat stress that causes severe bleaching on an annual basis by mid century.”
Coral bleaching occurs when corals lose their color after the symbiotic algae that live in coral cells and provide them with nutrients are expelled because of heat stress.
The longer this state of stress lasts, the longer the estranged algae stay away and the less likely that corals will recover. So scientists tend to distinguish between moderate bleaching, which can be managed, and severe bleaching, which can kill corals and also leave surviving corals more vulnerable to disease and several other threats.
The study comes after the unprecedented 2014-17 global bleaching event that produced devastating consequences to the Great Barrier Reef off Australia. .
The new survey of 100 major coral reefs, from 1980 through 2016, found only a handful that had not suffered severe bleachings during that time period. More striking, it found that the rate of severe bleaching is increasing over time. The average reef in the group bleached severely once every 25 or 30 years at the beginning of the 1980s, but by 2016 the recurrence time for severe bleaching was just 5.9 years.
The study said that as ocean waters have grown steadily warmer, global bleaching events are now triggered not only in warm water El Nino years, but potentially in any year, including cooler La Nina years.
The change has occurred during about 1.8 degrees Fahrenheit of overall global warming so far, highlighting that corals — whose existence, based on an ancient symbiosis with photosynthetic algae, evolved millions of years ago — are a particularly sensitive system.