9th International Coral Reef Symposium
It is now certain that coral reefs are being damaged by global climate change, the Bali meeting heard last week.
The first warning signs came from bleaching, which occurs when warmer waters force corals to expel their symbiotic algae. During the 1997-1998 El Ni-o, reefs bleached throughout the world, and there were mass deaths of coral in the Caribbean. Now cores drilled from Caribbean reefs off Belize show that nothing like this has happened for at least 3000 years.
"This is the first palaeontological evidence that directly links the new bleaching-related mass mortality to global warming," says Rich Aronson from the Dauphin Island Sea Lab in Alabama, who did the research. "It's clearly a cause for grave concern."
The tropics are bearing the brunt of global warming, Aronson says. Sea surface temperatures have risen by an average of 0.5 °C a decade, according to Alan Strong of the National Oceanic and Atmospheric Administration in the US. That's almost ten times the global average.
Aronson's work is supported by evidence from cores drilled at 16 reefs throughout the tropics, which have been analysed by Mark Eakin and his colleagues at the World Data Center for Paleoclimatology in Boulder, Colorado. "There is a definite increase in temperatures in the last 400 years, with warmer, wetter conditions." This must be a result of human activity, says Eakin. "The rate is extreme and we cannot explain it any other way."
Although Eakin thinks we are now entering a period of reduced El Ni-o activity, reefs are still vulnerable. There will be at least a doubling of atmospheric carbon dioxide, he says.
"You don't even need to believe in climate change," adds Joan Kleypas of the National Center for Atmospheric Research, also in Boulder. "You just need to believe emissions are going up. If you put more CO2 into the atmosphere, you put more into the ocean. That reduces pH, and in turn reduces reef calcification."
If current trends continue, corals may become too fragile to support reef structures as we know them, says Kleypas. There is no evidence to suggest corals are acclimatising to the changes, she says.
Reefs are worth an estimated $400 billion a year. A call for action to cut greenhouse emissions was unanimously supported by scientists at the meeting. "These results must be used immediately to make sure the Climate Change Convention is implemented properly," says Sue Wells of the World Conservation Union.
New Scientist issue: 4th November 2000
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