PLEA Network

9 March 2024, The Conversation: The Great Barrier Reef’s latest bout of bleaching is the fifth in eight summers – the corals now have almost no reprieve. For the fifth time in just the past eight summers – 2016, 2017, 2020, 2022 and now 2024 – huge swathes of the Great Barrier Reef are experiencing extreme heat stress that has triggered yet another episode of mass coral bleaching. Including two earlier heating episodes – in 1998 (which was at the time the hottest year globally on record) and 2002 – this brings the tally to seven such extreme events in the past 26 years. The most conspicuous impact of unusually high temperatures on tropical and subtropical reefs is wide-scale coral bleaching and death. Sharp spikes in temperature can destroy coral tissue directly even before bleaching unfolds. Consequently, if temperatures exceed 2°C above the normal summer maximum, heat-sensitive corals die very quickly. … This latest, still-unfolding event was entirely predictable, as ocean temperatures continue to rise due to global heating. Three of the seven mass bleaching events so far on the Great Barrier Reef coincided with El Niño conditions (1998, 2016 and this summer), and the remaining four did not. Increasingly, climate-driven coral bleaching and death is happening regardless of whether we are in an El Niño or La Niña phase. Average tropical sea surface temperatures are already warmer today under La Niña conditions than they were during El Niño events only three or four decades ago. The Great Barrier Reef is now a chequerboard of reefs with different recent histories of coral bleaching. Reefs that bleached in 2017 or 2016 have had only five or six years to recover before being hit again this summer – assuming they escaped bleaching during the 2020 and 2022 episodes. Attempts to restore depleted coral cover through coral gardening, assisted migration (by harvesting larvae) and assisted evolution (rearing corals in an aquarium) are prohibitively expensive and unworkable at any meaningful scale. In Florida, coral nurseries suffered mass deaths due to record sea temperatures last summer. The only long-term way to protect corals on the Great Barrier Reef and elsewhere is to rapidly reduce global greenhouse emissions. Read more here