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帽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.
鈥淭his is the first palaeontological evidence that directly links the new
bleaching-related mass mortality to global warming,鈥� says Rich Aronson from
the Dauphin Island Sea Lab in Alabama, who did the research. 鈥淚t鈥檚 clearly a
cause for grave concern.鈥�
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The tropics are bearing the brunt of global warming, Aronson says. Sea
surface temperatures have risen by an average of 0.5 掳C a decade, according
to Alan Strong of the National Oceanic and Atmospheric Administration in the US.
That鈥檚 almost ten times the global average.
Aronson鈥檚 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.
鈥淭here is a definite increase in temperatures in the last 400 years, with
warmer, wetter conditions.鈥� This must be a result of human activity, says Eakin.
鈥淭he rate is extreme and we cannot explain it any other way.鈥�
Although Eakin thinks we are now entering a period of reduced El Ni帽o
activity, reefs are still vulnerable. There will be at least a doubling of
atmospheric carbon dioxide, he says.
鈥淵ou don鈥檛 even need to believe in climate change,鈥� adds Joan Kleypas of the
National Center for Atmospheric Research, also in Boulder. 鈥淵ou 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.鈥�
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.
鈥淭hese results must be used immediately to make sure the Climate Change
Convention is implemented properly,鈥� says Sue Wells of the World Conservation
Union.
