– Scientists trying to size up the toll that climate change will take on Florida reefs may have found their answer at the bottom of the ocean on the other side of the world.

In a study published in the journal Nature Climate Change, a team looked at an ancient, buried volcano near the Mariana Islands in the Pacific Ocean where carbon dioxide bubbling from the sea floor mirrors projections for future levels of ocean acidification. The results? A real-world yardstick showing the point at which healthy reefs collapse and algae takes over, leaving a bleak rocky moonscape.

“It’s a grim picture,” said lead author Ian Enochs, an assistant scientist at the University of Miami’s Cooperative Institute for Marine and Atmospheric Studies.

Lab experiments have long led scientists to conclude that as the ocean becomes more acidic, coral and other sea life will suffer. Scientists worry because coral reefs provide a natural barrier against sea rise and more powerful hurricanes — two other byproducts of climate change. But while lab experiments have allowed them to examine changes species by species, they could only theorize about possibilities for complex reefs, an ecosystem filled with fish, anemones, sponges and a web of marine life working in tandem.

About two years ago, while Enochs was in the Mariana Islands, a U.S. territory, he heard about the bubbling sea floor near the Maug Islands. A two-day boat ride from an already remote chain of volcanic islands on the edge of the deepest trench in the world, they are like the glaciers of the sea. “Therein lies the adventure,” he said. “You have this amazing natural laboratory where you can look at what predictions for the end of the century look like today.”

The team picked three sites to study. One spot reflected carbon dioxide at levels now generally occurring in the ocean, a second had medium levels and the third lay nearest the vents where carbon equals projections for the next century. For three months, the team logged acidity, temperature and light.

Closest to the vents, the team found hardly any coral and the sea floor matted with algae. For the first time, researchers were able to document a complete shift from coral to algae. While a recent study found some coral might acclimate to increased levels of acidity, Enochs said near vents in Maug, where acidity occurs in amounts projected for the next century, coral did not adjust. “It absolutely gives us a measuring stick,” Enochs said.