Hotter oceans are putting coral reefs in peril worldwide. Scientists are warning that to save them, heat-trapping emissions must fall, and reefs will need more protection and restoration.

Transcript

STEVE INSKEEP, HOST:

One of the really affecting signs of climate change is the death of coral reefs. Many die as the oceans change. That's prompting scientists to ask what they can learn from certain coral reefs that seem to adapt. NPR's Lauren Sommer reports.

LAUREN SOMMER, BYLINE: As a marine biologist, Christopher Cornwall notices when people post photos of their snorkeling trips.

CHRISTOPHER CORNWALL: I've seen lots of people post pictures on the internet saying, look how great this reef is.

SOMMER: What they don't realize, he says, is that they're actually looking at coral skeletons. The oceans have absorbed most of the heat from human-caused climate change, and corals bleach in marine heat waves, turning white in the extreme heat. In his work at Victoria University of Wellington, Cornwall has seen this repeatedly on Australia's Great Barrier Reef.

CORNWALL: What happens is only a small fraction of that coral will be able to recover from those events, and a large proportion of those, depending on the heat stress, will die.

SOMMER: Cornwall says the oceans are also becoming more acidic, which makes it harder for reefs to grow. He and his colleagues found that if humans lower their emissions dramatically, some reefs will make it. But at high or even moderate levels of emissions, the majority of coral reefs will stop growing by the end of the century.

CORNWALL: If we miss this low-emission scenario target, the coral reefs are essentially doomed.

SOMMER: That has many scientists looking for ways to help corals adapt. I reached scientist Joanie Kleypas of the National Center for Atmospheric Research while she was in Costa Rica. The corals have bleached there, too. But she saw some hope at one of her projects.

JOANIE KLEYPAS: The corals survived. They were completely bleached for months and there was some mortality, but by and large, they survived. So they have some sort of secret.

SOMMER: The secret could be that they're better at handling heat. Kleypas says scientists are looking for these corals all over the world in the hope that they could breed them and restore reefs.

KLEYPAS: And if we act fast enough to execute that plan and we bring carbon dioxide emissions way down, then we do - we believe we have a chance.

SOMMER: If emissions remain high, Kleypas says, even helping corals adapt won't be enough. And corals are biodiversity hot spots that millions of people depend on for food, jobs and protection from storm surges.

KLEYPAS: This is just the first ecosystem, really major ecosystem, that we feel could collapse. So we have to do something. The eyes are on us.

SOMMER: Yes, it's pretty bleak, she says, which is why there's no time to waste.

Lauren Sommer, NPR News. Transcript provided by NPR, Copyright NPR.

Tags: coral reef  oceans  climate change