The Great Barrier Reef has suffered from another round of severe coral bleaching, with two-thirds of the Australian landmark now pushed to the limit. This was the second such event this year, and only the fourth overall, according to Professor Terry Hughes, one of the marine biologists leading the conservation effort.

Mass bleachings had previously only occurred in 1998, 2002 and 2016, with this latest event the first time a back-to-back occurrence has manifested itself since records were being kept.

A media release from the Australian Research Council outlined some of the reasons behind the most recent bleaching incident, with record-breaking temperatures outside of El Niño conditions mostly to blame. Whilst coral bleaching doesn’t necessarily mean the death of the corals in question, it is expected that there will be a high mortality rate amongst the latest batch of reefs to be affected. But how exactly does coral bleaching affect the reef and what is the process behind it?

As a direct result of climate change, sea temperatures have increased by almost 1˚ Celsius, this change in temperature has led the photosynthetic aspect of corals to be inhibited, leading to the loss of the zooxanthellae that is integral to corals’ ability to photosynthesize. In turn this leads to coral bleaching, which severely weaken coral reefs’ resilience and ability to adapt such events. Reefs have survived many bleaching events in the past, but they had several years to do so, as Dr. James Kerry explains, the latest event on the Great Barrier Reef is pushing an already stressed coral population to new levels:

“It takes at least a decade for a full recovery of even the fastest growing corals, so mass bleaching events 12 months apart offers zero prospect of recovery for reefs that were damaged in 2016.”

The compounding effects of the consecutive bleachings along with the damage from Tropical Cyclone Debbie’s landfall last week have greatly affected the GBR’s ability to adapt and heal itself. As Prof Hughes points out, climate change is the driving force behind these events, and without immediate action, it is likely that coral bleaching events will continue to degrade the Great Barrier Reef further.

“Clearly the reef in now struggling with multiple impacts, without a doubt the most pressing of these is global warming. As temperatures continue to rise, the corals will experience more and more of these events. Ultimately, we need to cut carbon emissions and the window to do so is rapidly closing.