A third mass coral bleaching event for the Great Barrier Reef

2018 to see Third Consecutive Mass Coral Bleaching Event for the Great Barrier Reef?

Robertscribbler,

22 January, 2018

One point two degrees Celsius hotter than average (1.2 C). That’s the temperature threshold where 50 percent of the world’s corals are likely to die off according to a scientific study written in Nature during 2013.

The El Nino year 2016 was about 1.2 C hotter than 1880s averages. Meanwhile 2017 was about 1.1 C warmer than normal despite a shift toward La Nina.

We are thus entering a very harmful period for the world’s corals. One in which corals are bleaching and dying off at unprecedented rates. The global bleaching event of 2014 through 2017 was the longest lasting and most damaging in the historical record. Many reefs around the world suffered severe losses. Reefs that had never bleached before experienced bleaching and mortality. And this event included severe damage to the majestic Great Barrier Reef of Australia.

Bleached Staghorn corals on Keppel Island Reef during 2016 event that impacted 93 percent of the Great Barrier Reef. Image source: UNESCO.

Unfortunately, despite an official end to the 2014 to 2017 global bleaching event, ocean temperatures across widespread regions remain at thresholds that are likely to result in stress to corals. And it is arguable that if bleaching were so widespread as it is now in past decades, then the present 2018 period would still be considered a global bleaching event.

Regardless of how we parse official declarations, reef systems are obviously still under stress. Just this past week, reports were coming in that sections of the Great Barrier Reef were bleaching for the third year in a row. The bleaching was rather widespread for this time of year. It was occurring earlier than normal — generating concern that 2018 bleaching could be worse than expected come February and March. It was hoped that the large reef system would be given a bit of respite from the heat. But now that particular hope is in doubt.

Corals around the world are still under threat from extreme ocean heat despite the fact that the 2014-2017 global coral bleaching event was officially ended during summer of 2017. Image source: NOAA.

Corals are one of the many canaries in the climate change coal mine. These organisms are a vital aspect of global ocean health and the reefs they build are the present home for upwards of 2 million species. Humans depend on corals for the food chains they support and for the natural beauty they provide. And a global ocean with less corals provides both less food and support for human beings and for ocean life as a whole.

Because corals are so sensitive to temperature change, it is expected that about 90 percent of the world’s corals will be lost if the Earth warms by 1.5 C. 

Meanwhile, virtually all of the corals (more than 95 percent) could be gone if the world warms by 2 C. With global temperatures at around the 1.1 C threshold and rising, we are in the danger range for corals at this time. And the world stands at the brink of losing the majority of this vital species with the potential to see 90 percent or more of the world’s corals lost over the next 3 decades under various scenarios in which fossil fuel burning continues.

Warmer than normal sea surface temperatures are again threatening Australia’s Great Barrier Reef (GBR). Jan 15, 2018 sea surface temperature anomaly image provided by Earth Nullschool.

Danger to corals is, today, a very immediate issue. And we are in the period of risk and damage now. This reality is highlighted by the fact that what should be a relative respite period for corals is still seeing abnormally high levels of bleaching.

During 2018, La Nina in the Eastern Pacific has generated relatively cooler surface waters in a number of locations. And we would normally expect La Nina to beat back global coral bleaching severity. However, an anomalous hot blob of ocean water between Australia and New Zealand is causing an unusual spike in ocean temperatures for the zone east of Australia (see image above). The result is that the GBR is again at risk.

Early bleaching for the Great Barrier Reef in 2018 is definitely a bad sign. However, scientists aren’t yet stating that this year will see bleaching intensity hitting levels similar to 2016 and 2017. Let’s hope that remains the case. But so long as fossil fuel burning and related warming continues, the road ahead for corals is one of existential crisis.