All year, it has been a real-time environmental catastrophe. The Great Barrier Reef, an unparalleled ecological treasure that supports all sorts of sea life and a range of human needs, not to mention a huge tourist economy, has seen the largest coral die-off ever recorded.

If this were a rare event, separated by many years from the next big die-off, the reef would rebound. But in the age of climate change, scientists say this and other tragedies are frighteningly likely to be compounded.

Experts have been tracking the destruction for months, announcing their final conclusions Nov. 29. They found that across a long stretch of the northern end of the reef, an average of 67 percent of the coral died, according to aerial and diver observations.

In these zones, the reef’s lively colors have been replaced by antiseptic white of “bleached” coral. Though weather events helped spare other areas this degree of destruction, the reef’s northern portions had been the most pristine.

In this case, the problem appears to have been water temperature, which was up to two degrees warmer than the normal summer peak. This threw off the delicate balance between the coral organisms and the algae that provide them sustenance. Natural variability may have played some role in raising the temperature — it was an El Niño year, which means the Pacific Ocean was hotter. But global warming probably set the scene.

Australian scientists concluded that this year’s coral crisis was rendered far more likely because of climate-change-related ocean warmth.

As the planet continues to warm, human influence will be more and more likely to interact with natural variation in dangerous ways. Among other things, that means all that dead coral may not have a chance to rebound.

Rising ocean temperatures, sadly, are not the only threat human greenhouse-gas emissions pose to coral. More carbon dioxide in the atmosphere translates into more acidic oceans, which erode coral structures. Then there are the more mundane threats that harm sea life, including coral. Fishermen use explosives to kill and capture ocean creatures. Urban and agricultural runoff makes water cloudy, inhibiting the photosynthesis on which reefs depend.

Scientists are racing to figure out how to help reefs survive the onslaught they are likely to face in coming years, examining corals that do better under stressful conditions and considering ways to preserve those that might struggle. But if human beings are to preserve crucial biodiversity — which comes with a range of benefits, from underpinning food chains to revealing lifesaving drugs — they have no choice but to curb the underlying problems.

Greenhouse-gas emissions must come down, and countries that are not properly managing their runoff or their fishing industries must tighten their rules.

Editorial by The Washington Post


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