Australia has warned that it will have to switch off the water supply to the continent's food bowl unless heavy rains break an epic drought - heralding what could be the first climate change-driven disaster to strike a developed nation. The Murray-Darling basin in south-eastern Australia yields 40 per cent of the country's agricultural produce. But the two rivers that feed the region are so pitifully low that there will soon be only enough water for drinking supplies. Australia is in the grip of its worst drought on record, the victim of changing weather patterns attributed to global warming and a government that is only just starting to wake up to the severity of the position.

The Prime Minister, John Howard, a hardened climate-change sceptic, delivered dire tidings to the nation's farmers yesterday. Unless there is significant rainfall in the next six to eight weeks, irrigation will be banned in the principal agricultural area. Crops such as rice, cotton and wine grapes will fail, citrus, olive and almond trees will die, along with livestock. A ban on irrigation, which would remain in place until May next year, spells possible ruin for thousands of farmers, already debt-laden and in despair after six straight years of drought.

Lovers of the Australian landscape often cite the poet Dorothea Mackellar who in 1904 penned the classic lines: "I love a sunburnt country, a land of sweeping plains." But the land that was Mackellar's muse is now cracked and parched, and its mighty rivers have shrivelled to sluggish brown streams. With paddocks reduced to dust bowls, graziers have been forced to sell off sheep and cows at rock-bottom prices or buy in feed at great expense. Some have already given up, abandoning pastoral properties that have been in their families for generations. The rural suicide rate has soared.

Mr Howard acknowledged that the measures are drastic. He said the prolonged dry spell was "unprecedentedly dangerous" for farmers, and for the economy as a whole. Releasing a new report on the state of the Murray and Darling, Mr Howard said: "It is a grim situation, and there is no point in pretending to Australia otherwise. We must all hope and pray there is rain." But prayer may not suffice, and many people are asking why crippling water shortages in the world's driest inhabited continent are only now being addressed with any sense of urgency. The causes of the current drought, which began in 2002 but has been felt most acutely over the past six months, are complex. But few scientists dispute the part played by climate change, which is making Australia hotter and drier.

Environmentalists point to the increasing frequency and severity of drought-causing El Niño weather patterns, blamed on global warming. They also note Australia's role in poisoning the Earth's atmosphere. Australians are among the world's biggest per-capita energy consumers, and among the top producers of carbon dioxide emissions. Despite that, the country is one of only two industrialised nations - the United States being the other - that have refused to ratify the 1997 Kyoto protocol. The governments argue that to do so would harm their economies.

Until a few months ago, Mr Howard and his ministers pooh-poohed the climate-change doomsayers. The Prime Minister refused to meet Al Gore when he visited Australia to promote his documentary, An Inconvenient Truth. He was lukewarm about the landmark report by the British economist Sir Nicholas Stern, which warned that large swaths of Australia's farming land would become unproductive if global temperatures rose by an average of four degrees.

Faced with criticism from even conservative sections of the media, Mr Howard realised that he had misread the public mood - grave faux pas in an election year. Last month's report by the UN Intergovernmental Panel on Climate Change predicted more frequent and intense bushfires, tropical cyclones, and catastrophic damage to the Great Barrier Reef. The report also said there would be up to 20 per cent more droughts by 2030. And it said the annual flow in the Murray-Darling basin was likely to fall by 10-25 per cent by 2050. The basin, the size of France and Spain combined, provides 85 per cent of the water used nationally for irrigation.

While the government is determined to protect Australia's coal industry, the drought is expected to shave 1 per cent off annual growth this year. The farming sector of a country that once "rode the sheep's back" to prosperity is in desperate straits. With dams and reservoirs drying up, many cities and towns have been forced to introduce severe water restrictions.

Mr Howard has softened his rhetoric of late, and says that he now broadly accepts the science behind climate change. He has tried to regain the political initiative, announcing measures including a plan to take over regulatory control of the Murray-Darling river system from state governments.

He has declared nuclear power the way forward, and is even considering the merits of joining an international scheme to "trade" carbon dioxide emissions - an idea he opposed in the past. Mr Howard's conservative coalition will face an opposition Labour Party revitalised by a popular new leader, Kevin Rudd, and offering a climate change policy that appears to be more credible than his. Ben Fargher, the head of the National Farmers' Federation, said that if fruit and olive trees died, that could mean "five to six years of lost production". Food producers also warned of major food price rises. Mr Howard acknowledged that an irrigation ban would have a "potentially devastating" impact. But "this is very much in the lap of the gods", he said.

How UN warned Australia and New Zealand

Excerpts from UN's IPCC report on the threat of global warming to Australia and New Zealand:
"As a result of reduced precipitation and increased evaporation, water security problems are projected to intensify by 2030 in south and east Australia and, in New Zealand, in Northland and eastern regions."

* "Significant loss of biodiversity is projected to occur by 2020 in some ecologically rich sites, including the Great Barrier Reef and Queensland's tropics. Other sites at risk include the Kakadu wetlands ... and the alpine areas of both countries."

* "Ongoing coastal development and population growth in areas such as Cairns and south-east Queensland (Australia) and Northland to Bay of Plenty (New Zealand) are projected to exacerbate risks from sea-level rise and increases in the severity and frequency of storms and coastal flooding by 2050."

* "Production from agriculture and forestry by 2030 is projected to decline over much of southern and eastern Australia, and over parts of eastern New Zealand, due to increases in droughts and fires."

* "The region has substantial adaptive capacity due to well-developed economies and scientific and technical capabilities, but there are considerable constraints to implementation ... Natural systems have limited adaptive capacity."
(By Kathy Marks, The Independent, 20/04/2007)