Michael McCarthy: Why put one of the Earth's last pristine reefs at risk?

They're the world's richest ecosystems. They're also the world's most threatened ecosystems. Why would you want to add to the risks now facing coral reefs, when you don't have to?

That will be a question to which Australia's leaders will struggle to find a convincing answer, should they take the virtually unthinkable decision to license Shell's proposed oil drilling close to the Ningaloo Reef. For there has never been a time when the threats to coral reefs have been clearer. Two weeks ago, the most comprehensive assessment of the health of the "rainforests of the sea" was released by the World Resources Institute (WRI). It contained a dire message: three-quarters are now threatened with destruction by human activities.

Overfishing, especially destructive fishing with explosives, is the most immediate threat, but there are also major pollution threats from agriculture and industrial development.

And all reefs are further at risk from two global threats associated with climate change: "bleaching" when the coral organisms themselves are unable to support higher water temperatures, and ocean acidification, brought about by carbon dioxide dissolving into seawater and producing carbonic acid.

Coral reefs in their natural state are immensely productive – it has been estimated that between a quarter and a third of all marine fish species live in association with them – and they directly support the livelihoods of nearly 300m people. Last year, the UN estimated their economic worth at $172bn annually.

Yet the WRI's report shows most on the road to destruction. In South-east Asia, nearly 95 per cent of reefs are threatened; in the Atlantic region, more than 75 per cent; in the Indian Ocean, more than 75 per cent; in the Middle East, more than 65 per cent.

In fact, the one bright spot in the report was Australia, with only 14 per cent of reefs threatened by local activities, and a mere 1 per cent facing a very high threat. Australia is the last real haven for the world's coral reefs; and now Shell wants to invade even that.

Never mind the Gulf disaster; Australians have had their own warning: the Montara spill in the Timor Sea two years ago. The Australian federal government and the government of Western Australia don't need to take that risk with Ningaloo. It might like the revenues, but it doesn't have to have them.