Climate change is the obvious culprit. As we pump increasing amounts of carbon dioxide into the skies, the world warms, and that includes the oceans. At the same time, plenty of excess carbon dioxide gets absorbed into the oceans too, and this generates carbonic acid, which eats away at the calcium carbonate exoskeletons.
“The impacts that we are already seeing today are the result of close to 1°C (1.8°F) increase in average global temperature,” Schoepf pointed out.
When asked about the Paris agreement’s more ambitious lower limit of 1.5°C (2.7°F), the response wasn't one imbued with much hope.
“While it is absolutely critical to limit further warming as much as possible, 1.5°C warming will nevertheless mean even more bleaching than we have seen to date,” she noted.
That’s not all there is to the story though; El Nino and La Nina, collectively known as the El Nino-Southern Oscillation (ENSO), also plays a major role.
To put it simply, this periodic climate phenomenon has a planet-wide impact on atmospheric and oceanic systems. With regards to the Pacific Ocean, El Nino is the warm phase and La Nina is the cold phase.
These temperature fluctuations have always had an effect on coral reefs, but this new study highlights how times have changed dramatically. Today, the cold La Nina phase is now hotter than the warm El Nino phase back in the early 1980s.
“Our analysis indicates that we are already approaching a scenario in which every hot summer, with or without an El Nino event, has the potential to cause bleaching and mortality at a regional scale,” the study concludes.
Coral reefs are more biodiverse than tropical rainforests, and 25 percent of the world’s fish biodiversity alone is associated with them. At the same time, they generate $30 billion in goods and services every single year.
Whether you’re more concerned about extinctions or the economy, it doesn’t matter. If reefs die out, we will be living in a poorer world, no matter how you measure it.