Coral bleaching events ‘now every six years’
The Great Barrier Reef has now bleached four times since 1998, including for the first time during back-to-back events in 2016 and 2017.
The world’s coral reefs are under increasing threat, scientists have warned, after new research shows an escalating rate of bleaching events over the past four decades.
For the first time, an international team of researchers studied the rate of coral bleaching at locations throughout the tropics.
Their findings, published in the journal Science, show that the time between bleaching events has reduced from once every 25-30 years in the early 80s, to once every six years on average since 2010.
Lead author Professor Terry Hughes, said: “The climate has warmed rapidly in the past 50 years, first making El Niños dangerous for corals, and now we’re seeing the emergence of bleaching in every hot summer.
“For example, the Great Barrier Reef has now bleached four times since 1998, including for the first time during back-to-back events in 2016 and 2017, causing unprecedented damage.”
Coral bleaching is a stress response when reefs are exposed to elevated ocean temperatures. When bleaching is severe and prolonged, many corals die.
Co-author Professor Andrew Baird, from the ARC Centre of Excellence for Coral Reef Studies (Coral CoE), said: “It takes at least a decade to replace even the fastest-growing species.”
Mass bleaching of corals was “unheard of” before the 80s, Prof Hughes added - even during strong El Niño conditions. However, repeated bleaching events and mass mortality of corals has become “the new normal” around the world, as a result of rising temperatures.
The study suggests that tropical sea temperatures are now warmer during cooler-than-average El Niña conditions than 40 years ago during El Niño periods. Prof Hughes said he hopes the “stark results” will spark tougher action to reduce greenhouse gases in Australia, the US and elsewhere.
