Great Barrier Reef Coral Bleaching and High Sea Temperature Could Become a Customary Event by 2050

A new study carried out by researchers from the University of Melbourne suggests that the temperatures that caused distressing coral bleaching on the Great Barrier Reef last year will likely become a norm by 2050 unless steps are taken to cut greenhouse gas emissions quickly.

Bleaching due to high sea surface temperatures is a catastrophic event for coral reefs. Corals can die abnormal heat make them expel their symbiotic algae. Sea surface temperatures are now so high across much of the tropics that many reefs are suffering severe bleaching for consecutive fourth year. Many divers in Australia have already reported new bleaching in the northern part of the Great Barrier Reef. Natural history film-maker Biopixel has released a new video showing new bleaching on the reef. The Great Barrier Reef Marine Park Authority has also requested visitors to report any signs of bleaching after a second year of unusually high water temperatures.

Last year, the sea surface temperatures on the Great Barrier Reef were the hottest on record in the months of February, March and April. As a result, the largest ever coral die-off on the Great Barrier Reef was recorded, with almost two-thirds of corals dying in the 700 kilometres north of Port Douglas in far north Queensland.

Dr Andrew King, a climate scientist from the University of Melbourne who led the research says temperatures like March 2016 are likely to become very common by the 2030s and 2040s if emissions are not cut significantly and quickly.

In 2030, there would be a 70 per cent chance of having temperatures similar to March 2016. In 2050, that chance would be 97 per cent.

“Beyond that [the 2016 temperatures] become much cooler than average, to the point that by the late 21st century an event like 2016 would actually be remarkably cold,” Dr King said.

Scientists believe coral can tolerate high temperatures once in every five years, and the recovery process takes about 10 to 30 years.

In this study, Dr King ran several climate models under a high-emissions scenario and low-emissions scenario, and found that high water temperatures are likely to occur more frequently if emissions are not curbed quickly and significantly. The study also revealed that even under reduced-emissions scenario, the high water temperatures would occur as often as every second year.

“The event that we saw in March 2016 is roughly the kind of event that we’d expect every four years from now on in the next few years, becoming more frequent after that,” Dr King said.

“By the 2030s it would be once every two years.”

Dr King’s study does show that the reef’s prospects could be improved with human efforts to cut emissions.

“If we do take action, we do have some positive influence that results in a reduced chance of bleaching later in the 21st century, relative to if we don’t do anything at all,” he said.

“We need much stronger action than we’re seeing from any countries, but Australia in particular is not doing anywhere near enough,” he said.

“We need to reduce our greenhouse gas emissions and we need to make policies that are conducive to that — we need to shift away from power sources like coal … towards renewable energy.”

“[Emissions] would need to drop quite rapidly in the next few years in order to have any chance of achieving the RCP 2.6 scenario or indeed the Paris goals of limiting warming to 1.5 or even 2 degrees Celsius.”