Extreme temperature swings thousands of years ago caused a dramatic shutdown in coral reef growth that lasted more than two millennia — a finding that makes controlling climate change today all the more pressing, a new study suggests.

A team of marine biologists drilling into coral reefs off the Pacific coast of Panama found that reefs in the area had stopped growing about 4,000 years ago due to natural climatic shifts.

The lead author of the study, Richard Aronson, with the Florida Institute of Technology, told CBC Radio's As It Happens on Friday that the reefs in Panama didn't resume growth until 2,500 years later.

"It's important because it tells us that when bad things happen to reefs, it can shut them down for a long period of time," Aronson said, speaking from Melbourne, Fla. "Our biggest mystery, then, was to figure out what exactly had happened, and we were able to pin that shutdown of reefs on climate and, in particular, the variability of the El Nino southern oscillation, of which El Nino events are a part."

Aronson explained that a "climatic seesaw" in the Pacific caused hot water to "bleach" and damage the coral and cold water from La Nina weather patterns to suppress its growth.

Flattening of reefs

The death of corals causes their skeletons to collapse, and the reef zone to flatten.

"That means it doesn't have the cavities and crevices that fish and octopuses and conches and crabs and all the other inhabitants of the reef depend on, so they go away," Aronson said. "So what you're left with is essentially a pile of rubble that can be covered with algae or just covered by sand, as compared to a vibrant reef with coral branches growing everywhere and lots of things living in it."

Aronson said it's not too late to reverse global warming and ocean acidification by capping greenhouse gas emissions.

"The window is closing, but it's still open. Now is the time to act and this is certainly not the time to give up and say it's all over," he said. "This is the time we need to be fighting the hardest to save coral reefs and all the other natural habitats on the planet."

The findings were published in the latest issue of the journal Science.