When the temperature soars, coral reefs might cool off by creating their own clouds.

Research from the Great Barrier Reef off the Australian coast shows that corals are packed full of the chemical dimethyl sulphide, or DMS. When released into the atmosphere, DMS helps clouds to form, which could have a large impact on the local climate, reports New Scientists.

In the air, DMS is transformed into an aerosol of tiny particles on which water vapour can condense to form clouds. This sulphur compound is also produced in large amounts by marine algae and gives the ocean its distinctive smell. Algae play a vital part in regulating Earth’s climate, but no one had looked at whether coral reefs might have a similar role.

Graham Jones of the Southern Cross University in Lismore, Australia, and colleagues measured DMS concentrations in corals in the Great Barrier Reef and its surrounding water. They found that the mucus exuded by the coral contained the highest concentrations of DMS so far recorded from any organism. A layer rich in DMS formed at the sea surface above the reef, where it was picked up by the wind.

"Although globally the emission of DMS from the Great Barrier Reef is not huge, on a regional basis it is very significant," says Jones.

The big question now is what effect this will have on the climate. "The coral is a concentrated source of DMS, which could affect the formation of clouds in that region," says Peter Liss, an environmental chemist and DMS expert at the University of East Anglia, Norwich, UK.

The Australian team plans to study the impact of the reef and other corals on local climate over the next few years. "We don’t know how the DMS emitted by the coral relates to cloudiness and the radiative climate over the reef," says Jones. "That’s the missing link."

But their findings help to solve a 30-year puzzle. Surveys in the 1970s found very high concentrations of aerosol particles in the air above the Great Barrier Reef. The coral was thought to be the source, but the mechanism by which the reef might have caused the aerosol count to soar was not known. "They didn’t know about DMS in the 1970s," says Jones.

The research also raises another intriguing possibility: that coral can use a Gaia-like feedback mechanism to regulate the amount of sunlight they are exposed to. The "Gaia theory" is that life on Earth regulates its environment to keep itself healthy.

In lab experiments, Jones and his team showed that corals produce more DMS when the symbiotic algae inside their tissues become stressed by high temperatures or UV radiation. If this DMS seeds more clouds, the coral could have evolved a way to reduce the water temperature or UV exposure. "We’ve got a long way to go to conclusively demonstrate this, but we’ve got a lot of ammunition," says Jones.