Some of the worst effects of climate change on coral reefs weren't supposed to happen for decades—and some researchers thought they wouldn't happen until the end of the century. But a new study shows that ocean acidification—caused by excess CO2 in the air—is already dissolving coral now.
In the study, researchers looked at two years of data from seven points around reefs in the Florida Keys. In some places, the reefs were dissolving more quickly than they were rebuilding, a process called net erosion.
In the past, studies were either done in the lab—where it's impossible to recreate the complex environment of an actual reef—or over very short periods, often just a week long, and not looking at variations by season. So when past estimates suggested that reefs wouldn't start disintegrating until the middle or end of the century, they weren't based on full data.
This doesn't mean that coral reefs are going to immediately disappear, but it's a wakeup call.
"The important message is first that these measurements are really sensitive, and they're a leading indicator—they're telling us the direction of a trend," says Chris Langdon, chair of the University of Miami’s department of marine biology and ecology and lead author of the study. "It's very early on—like the patient's only lost a few pounds so far, and if we fix the diet or fix the disease, they can easily recover. But if we don't do anything, which is sort of what's happening, it's only going to get worse."
It's possible that the situation now is already worse than when the researchers first collected data, in 2009 and 2010. Since then, during the two hottest years on record—2014 and 2015—extensive bleaching killed portions of the reef, making it even more susceptible to dissolution. As the reef dies, it loses a protective layer of tissue, and other tiny organisms can drill into coral skeletons, so they fall apart faster.
While it's possible, in theory, to temporarily reverse ocean acidification around a reef by dumping a basic solution in the water, it's not exactly feasible on the scale of the ocean (and large-scale planetary engineering may be inadvisable anyway).
"The only solution is really reducing CO2 emissions," Langdon says. "Facing up to that and actually accomplishing something are going to take a long time. The sooner we start, the less CO2 continues to build up in the atmosphere, the easier it's going to be to reverse things."