Mass coral bleaching events are going to become routine as ocean temperatures continue to rise, according to a new study published this week in the journal Science.
An international team of researchers documented the time between coral bleaching events across the tropics, and at each location found that the interval has diminished five-fold in the past three to four decades.
In the early 1980s, mass coral bleaching events only occurred every 25 to 30 years, but they have happened roughly every six years since 2010.
Bleaching is a stress response to elevated ocean temperatures in which corals expel the colourful algae that live in their tissues. If bleaching is prolonged and severe, many corals die — and it can take more than a decade to replace even the quickest-growing species.
“Before the 1980s, mass bleaching of corals was unheard of, even during strong El Niño conditions,” says says lead author Professor Terry Hughes, director of Australia’s ARC Centre of Excellence for Coral Reef Studies. “But now repeated bouts of regional-scale bleaching and mass mortality of corals has become the new normal around the world.”
Mass bleaching was first recorded in the 1980s and 1990s during hotter-than-average El Niño warming cycles. However, the phenomenon now occurs in every hot summer — even under La Niña ocean cooling conditions.
“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,” explains Hughes.
The scientists hope that their results will further highlight the need to reduce greenhouse gases in high-emissions countries.