The last global coral bleaching event that inflicted a degree of damage comparable to the one we are now experiencing occurred during 1997 through 1999. Back then, global annual surface temperatures hit a peak of 0.85 degrees Celsius hotter than 1880s averages and ocean temperatures in many regions hit a range of 29-30 C or more. This warming-spurred event generated never-before seen wreckage among the world’s corals.
(Pacific Ocean sea surface temperatures are again warming as the Equatorial region progresses toward a predicted 2017 El Nino. Sea surface temperature anomalies of 1-2 C above average are now very widespread with embedded hot spots that contain 2-4 C above average temperatures [see above map]. These anomalies are enough to continue a global coral bleaching event that has now lasted for four years. Image source: Earth Nullschool.)
The 2014 to 2017 Global Coral Bleaching Event
In 2014, annual average global temperatures began to exceed 0.9 C above 1880s values before climbing to a 1.06 C departure in 2015 and a 1.2 C departure in 2016. This surface warming — spurred in part by increasingly warm surface waters — set off a coral bleaching event the world over that has now lasted four years. An event that presently has no end in sight. One that is now considerably worse than the 1997-1999 bleaching in a number of key measures.
During 2017, ocean surface temperatures are again expected to warm as a weak-to-moderate El Nino is predicted to form. Meanwhile, global atmospheric 2 meter temperatures will likely remain in a range of 1.1 to 1.3 C above 1880s values for the year. As a result, global coral bleaching is still very widespread and is expected to continue for the foreseeable future.
(Considerable coral bleaching is predicted for the next four months in NOAA’s Coral Reef Watch report.)
According to NOAA’s Coral Reef Watch:
…in the central equatorial Pacific, bleaching heat stress continues to build. The Austral Islands are now at Alert Level 2 bleaching stress (associated with widespread coral bleaching and significant mortality), and the Southern Cook Islands are at Alert Level 1 (associated with significant coral bleaching) – with an expected escalation to Alert Level 2 stress in the next 1-4 weeks. Alert Level 2 conditions are also expected in the Northern Cook Islands, the Samoas, Wallis & Futuna, Northern Tonga, Southern Tonga, the Tuamotu Archipelago, the Society Archipelago, the Pitcairne Islands, and Easter Island, Chile in the next 1-4 weeks. Alert Level 1 bleaching stress is anticipated in the Southern Line Islands, Tuvalu, and the Marquesas Islands in the next 5-8 weeks.
Back-to-Back Bleaching for Great Barrier Reef Somewhat Mitigated by Debbie, Seychelles Concerns Increase
Australia’s national treasure — Great Barrier Reef — was, this year, undergoing a second extreme coral bleaching event comparable to the 2016 bleaching which wiped out an estimated 22 percent of the reef’s living corals. That’s 1 in 5 corals gone in just one year. And with a second mass coral bleaching now underway, anxieties over the staggering impacts to this precious living system are running high. That said, recent reports indicate that Hurricane Debbie has delivered somewhat cooler waters to sections of the reef — raising some hopes that the 2017 event may be less harmful than predicted.
Professor Terry Hughes, a world-renowned coral reef expect, continues to offer notes of concern stating that “Cyclone Debbie has come a month too late and in the wrong place to prevent mass bleaching.” Sea surface temperature maps indicate that while some sections of the reef have seen cooler waters, other sections continue to see water temperatures in a range warm enough to cause bleaching. In addition, many reefs had already bleached prior to the arrival of Debbie. What can be said is that though bleaching has been considerable during 2017, and probably comparable to 2016 for many regions, it would have been worse had Debbie not delivered cooling to some sections.
(Consensus models predict a moderate-strength El Nino during 2017. Such an event would likely continue to keep ocean surfaces warm enough to generate widespread bleaching. Image source: NOAA.)
In addition to noted mass bleaching in the Great Barrier Reef and in numerous other Pacific reefs as indicated by NOAA’s Coral Reef Watch report, anxieties are now running high in the Seychelles. This Indian Ocean island chain is currently seeing mass bleaching among many corals. Now, only 3-5 percent of corals remain alive at a widespread number of locations following 2016’s extreme ocean warming. Experts suggest that many Seychelles reefs will require about 15 years to recover. Unfortunately, human-forced global warming through fossil fuel burning is likely to deliver continued bleaching stress to the Seychelles and a rather wide range of other reefs during multiple years to follow.
The issue is that global temperatures have now reached a threshold that is likely to produce mass bleaching during most years and that these temperatures continue to rise. It is unlikely that we will ever see another year that is even as cool as the 1997-1999 El Nino that produced the last major global coral bleaching event. And so we are entering a time of continuous peril for the world’s reefs.
Hat tip to Unaturalfx