First, hurricanes are essentially heat engines, spawned only over warm ocean waters The warmer the water, the stronger the hurricane can be. Forecasters were left scratching their heads in bewilderment as the familiar swirl of clouds, complete with a well-defined eye, appeared in an ocean basin where none had been spotted before.Hurricane Catarina struck Brazil with 90mph winds, causing up to a dozen deaths. Hurricane monitoring services may now have to be extended 2,000 miles to the south of the equator to deal with the new threat.The stormy weather was followed by an equally stormy debate among tropical meteorologists about whether the fingerprint of global warming may be to blame. One, Chris Landsea from the Hurricane Research Division in Miami, even resigned from the intergovernmental Panel on Climate Change, accusing it of bias.But even from a debate this politicised, a few facts do stand out.
There is clear evidence that tropical Atlantic sea-surface temperatures are rising, and a broad acceptance that at least some of this must be down to human-caused global warming. And that was just in the Atlantic; in the Pacific, Japan was struck by a record number of typhoons, several also wreaking havoc in Taiwan, China and the Korean peninsula.And, for the first time on record, the southern Atlantic also spawned a hurricane. He estimates that overall a sixth of tropical corals were destroyed. "If we lost that proportion of the rainforests in a single year, people would be screaming," he says.Dr Hoegh-Guldberg calculates that within 20 to 30 years, disasters on the scale of 1998 will become annual events, putting the survival of tropical reefs at risk.HurricanesCoastal residents in Florida could be forgiven for keeping a nervous eye on the horizon now that this year's hurricane season has started. Unless the corals can recover quickly, invasive algae appear, covering the dead reefs in choking grey sheets.In 1998, an El Ni?ear, and still the hottest globally on record, huge swaths of reef were killed, particularly in the Indian Ocean, which suffered 90 per cent mortality rates in some areas.
The Australian marine biologist Ove Hoegh-Guldberg called it "the most serious human impact on an ecosystem ever". As sea surface temperatures rise under the baking sub-tropical sun, these tiny creatures - whose calcium carbonate skeletons form the famous reefs - begin to suffer a kind of marine heat-stroke. The coral polyps expel their companion algae and turn bone white in an increasingly-frequent event known as "bleaching".Coral reefs are the most biologically diverse ecosystem in all the seas, holding nine million types of plants and animals, including a quarter of all known ocean fish. Yet bleaching events have devastated large sections of reef across the world.