Coral reefs may grow with global warming

Rising levels of greenhouse gases may not be quite as bad for coral reefs as was previously thought. A team of Australian scientists say that the damage done by increasing amounts of carbon dioxide in the oceans will be offset by warmer waters, which will make coral grow faster. But other researchers counter that warming will do more harm than good.
An increase in the amount of dissolved CO2 reduces the levels of calcium and carbonate ions in seawater, which are needed to make corals. But the effect of rising water temperature on corals has been less well understood.
So Ben McNeil of the University of New South Wales in Sydney, Australia, and colleagues modelled the interactions between the atmosphere, oceans and ice, and calculated the sea surface temperature and the levels of calcium carbonate in the water up to 2100. Then they estimated how these changes would affect the formation of corals.
They found that warmer water would increase the rate of coral formation, or calcification, and that this would outweigh the detrimental effect of lower levels of calcium carbonate in the seawater. They predict that by 2100 corals will be growing 35% faster than today.
Coral bleaching
Other researchers argue that McNeil’s team did not consider coral bleaching, which occurs when warmer waters cause corals to expel the symbiotic algae that live in them. They say bleaching may undo the beneficial effects of higher temperature.
“They are correct in saying that if you heat a coral up, it will work faster,” says coral expert Charles Sheppard at the University of Warwick, UK. “But a rise in temperature does other things too, such as kill the algae, which ultimately kills the coral and reduces calcification to nothing.”
McNeil claims that bleaching may not always kill coral. “The scientific evidence for a permanent state of bleaching is quite weak,” he says. “Corals recover and adapt to some extent.”
But Sheppard is sceptical that coral can adapt fast enough. “There are increasing indications that corals are creeping towards higher latitudes and hollowing out in the tropics. Bleaching is making them die left, right and centre.”
Journal Reference: Geophysical Research Letters (DOI: 10.1029/2004GL021541).
(New Scientist)