CANBERRA - A widening of the world's tropical belt that will turn Sydney's climate into that of Brisbane will hammer Aboriginal communities and the poor nations of Asia and the Pacific, new studies warn.
The studies say there is already evidence that the tropics are moving further north and south in a trend that will also extend the range of sub-tropical climates, drying out present fertile regions with devastating effects on health and food production.
James Cook University Vice-Chancellor Professor Sandra Harding said tropical climates had already moved more than six degrees of latitude beyond the traditional confines of the Tropics of Cancer and Capricorn, and were continuing to expand.
About half the world's population, including most of its poorest and least educated, lived in tropical climates that were also home to 80 per cent of plant and animal species, and which generated about 20 per cent of the planet's wealth.
"It is in the tropics where we have new and dangerous diseases evolving and spreading," Harding said.
"According to genetic studies, about 80 per cent of infectious diseases arise in the tropics, with many new illnesses resulting from viruses that jump from animals to humans.
"And it's in the tropics that we are seeing massive extinction of plant and animal life, the loss of indigenous cultures and deforestation on a scale that is scarcely imaginable."
Harding's warning, based on a new James Cook University review of the scientific literature on climate change, was echoed by a report by the aid group Oxfam, which found that formerly distinct seasons are shifting, destroying harvests and causing widespread hunger.
"Climate change is the central poverty issue of our times," Oxfam Australia climate change policy adviser Julie-Ann Richards said.
"Climate change is happening today and the world's poorest people, who already face a daily struggle to survive, are being hit hardest."
The university's review said that the impact of the widening of the tropical belt would be further deepened by the expansion of the world's subtropical dry zone, which was expected to cause longer and more frequent droughts.
Regions of temperate Mediterranean climate bordering the subtropics were particularly vulnerable, and were already experiencing the effects of climate change.
Southwestern North America was expected to see an "imminent shift" to a more arid climate, California was at present in the grip of an extended drought, and significant drying had been observed over the past 50 years in southern Western Australia.
"If the dry subtropics expand into these regions the consequences could be devastating for water resources, natural ecosystems and agriculture, with potentially cascading social and health implications," the review said.
Australia was expected to be one of the hardest-hit regions, with a significant increase in drought for much of its southern half and the extension of arid conditions to heavily populated temperate regions such as northern New South Wales, Perth, and potentially even further south, into Victoria.
Remote Aboriginal communities would be especially at risk.
Animal and plant species, especially those whose ability to migrate was limited, would be devastated: in the northern NSW heatwave of 2002 more than 2500 bats of two species died in a single day as temperatures hit 42C.
Tropical cyclones would become more severe and reach further south, serious flooding would increase in Queensland and across northern Australia, and tropical diseases such as dengue fever would move south.
Worldwide, the Oxfam study said evidence of the impact of climate change was already mounting. Rice and maize crops, on which hundreds of millions of people depended, faced significant falls in yield.
Evidence of changing seasons was already emerging from countries such as Bangladesh, Uganda and Nicaragua, where farmers were facing repeated crop failures.
Health was increasingly at risk, with estimates that climate change had contributed to an average increase of 150,000 a year in deaths from tropical diseases like malaria and dengue fever.