Ocean acidification can also bring down reefs because it affects the corals themselves. Corals can make their calcareous skeletons only within a special range of temperature and acidity of the surrounding seawater. But the oceans are acidifying as they absorb increasing amounts of carbon dioxide from the atmosphere. Research led by Ove Hoegh-Guldberg of the University of Queensland shows that corals will be pushed outside their temperature-acidity envelope in the next 20 to 30 years, absent effective international action on emissions.

We have less of a handle on pollution. We do know that nutrients, particularly nitrogenous ones, are increasing not only in coastal waters but also in the open ocean. This change is accelerating. And we know that coral reefs just can’t survive in nutrient-rich waters. These conditions only encourage the microbes and jellyfish that will replace coral reefs in coastal waters. We can say, though, with somewhat less certainty than for overfishing or ocean acidification that unstoppable pollution will force reefs beyond their survival envelope by midcentury.

This is not a story that gives me any pleasure to tell. But it needs to be told urgently and widely because it will be a disaster for the hundreds of millions of people in poor, tropical countries like Indonesia and the Philippines who depend on coral reefs for food. It will also threaten the tourism industry of rich countries with coral reefs, like the United States, Australia and Japan. Countries like Mexico and Thailand will have both their food security and tourism industries badly damaged. And, almost an afterthought, it will be a tragedy for global conservation as hot spots of biodiversity are destroyed.

What we will be left with is an algal-dominated hard ocean bottom, as the remains of the limestone reefs slowly break up, with lots of microbial life soaking up the sun’s energy by photosynthesis, few fish but lots of jellyfish grazing on the microbes. It will be slimy and look a lot like the ecosystems of the Precambrian era, which ended more than 500 million years ago and well before fish evolved.

Coral reefs will be the first, but certainly not the last, major ecosystem to succumb to the Anthropocene — the new geological epoch now emerging. That is why we need an enormous reallocation of research, government and environmental effort to understand what has happened so we can respond the next time we face a disaster of this magnitude. It will be no bad thing to learn how to do such ecological engineering now.