Corals are in peril. Life without them would be dire

This broiling year is turning out to be a window onto a grim possible future in which global warming leaves humanity with a vastly different and less hospitable planet.

Nowhere is this more apparent than in the fragile reef ecosystems built by corals, to the benefit of other marine life and humans alike. Now, with ocean temperatures soaring, corals are in extreme peril. Our warming path could push them to extinction.

The repercussions of a world without corals would be dire. More than a quarter of the planet’s sea life depends on reefs, and 1 billion humans need them and the creatures they support for food and livelihood. Reefs protect coastal settlements from storms and floods. They are sources of compounds used in treatments for cancer and other diseases. Oceans without coral would eventually be starved of fish, forcing farmers to produce more protein on land, a far costlier process. The water would be slimier, choked with algae and jellyfish. Oceans would produce less oxygen.

Unfortunately, humans have taken corals for granted for too long. Scientists estimate the world has lost more than half its reefs since 1950, even before the planet truly started cooking. Overfishing, pollution, physical destruction, thoughtless tourists and more have been stressing out reefs for decades, softening them up for humanity’s death blow: global warming caused by greenhouse gases.

The ocean soaks up atmospheric heat and is slow to let it go. The vast majority of the excess warmth humans have produced over the decades has ended up in the ocean, driving water temperatures to record highs. Most corals can’t survive even a 1 degree Celsius change in temperature for very long. With the planet now having warmed approximately 1.2C over preindustrial averages, coral deaths are accelerating. According to one count, 15% of the world’s corals died in a coral-bleaching event in 2014-17 alone. Half the world’s remaining corals could be dead by 2035, according to a University of Hawaii study.

At the moment, many corals that remain are those hanging on for dear life in deeper, cooler water. But warming the planet by 1.5C, on average, would eliminate many of those havens, according to a recent study. Warming it by 2C would destroy most cool retreats, leaving corals with nowhere to hide and possibly resulting in the extinction of 99% of them. Current human practices have the world on a path to nearly 3C of warming.

Fortunately, the long-term global heating trend isn’t expected to reach 1.5C for many years, if not decades. But a strong El Niño weather pattern this year, warming the eastern Pacific, could cause a temporary spike to such levels. Past coral die-offs, including the one in 2014-17, have taken place during El Niño events.

Even without El Niño’s effects, which shouldn’t peak until later this year, the ocean is already dangerously warm for corals in many places. Bleaching – which happens when beneficial algae flee corals because of heat, leaving them without food, color and protection from disease – began at least a month early in Florida’s waters this year, according to the National Oceanic and Atmospheric Administration. The weather pattern has at least another month to go. Many corals might never recover. In the Florida Keys, where water temperatures recently spiked to 100F (38C), corals on Sombrero Reef skipped the bleaching part and simply cooked to death.

The good news is that corals have been around for more than 500 million years. They have endured mass extinctions of coral species and climate change before. But they typically had much longer to adapt than humans have given them by pumping carbon into the atmosphere at a speed unprecedented in the geologic record. It has also taken corals millions of years to regain full strength after extinction events. Some species better tolerate heat but tend to grow slowly and don’t provide the same benefits to fish and humans.

Most important, humans must stop burning fossil fuels as quickly as they can to keep the oceans from warming even more. In the absence of that, as a last resort, reef-restoration groups such as the Coral Restoration Foundation are building Noah’s Arks of coral species, preserving their biodiversity for a day when the water is somehow more hospitable. We still have the power to decide whether that day will ever come.