A government scientist has warned that climate change, and specifically the rising levels of greenhouse gases in the atmosphere, is pushing up toxins and lowering nutrients in eucalyptus leaves.
Dr Dan Lunney, of the New South Wales Department of Environment and Climate Change, said the trend would force koalas out of trees and on to the ground to search for food, putting them in danger.
"What currently may be good koala habitats will become very marginal habitats," he said. "This means koalas have to change trees more often to get to the leaves they need.
"As koalas change trees they have to walk across the ground, if they walk across the ground they are vulnerable to dogs and if there are roads in the middle they are vulnerable to cars as well."
Koalas are already listed as a vulnerable species. Among the biggest threats to their survival are land clearing, bushfires and drought.
But they are also notoriously fussy eaters. Of Australia's 700 different types of gum tree, they will only eat the leaves of 25. The large grey marsupials, known for their bear-like looks and passive nature, sleep for 20 hours each day because the leaves they eat provide them with so little energy.
Conservationists recently called on the federal environment minister to urgently declare south-east Queensland's koala population critically endangered after numbers fell from 25,000 to 4,000 in ten years.
Post-mortem examinations of around 700 koalas in the region found most were "wasted" – or starving – when they died.
Professor Ian Hume of Sydney University said he has been "waving the yellow flag" about the consequences of toxic eucalyptus leaves for years.
Healthy koalas produce one offspring a year, but those living in "sub-optimal habitats" may only produce one cub every three to four years, he told The Daily Telegraph.
"We know global climate change is happening and its going to challenge many different things some of them which will be so subtle we won't actually know about them until suddenly we realise – well that's right, there used to be koalas in that patch of forest and they aren't there any more," he said.
"We wouldn't see them lying dead on the road, we would see them declining in number because they are reproducing at a slower rate."
Prof Hume warned there is little time to reduce the effects of climate change on koalas.
"They are clinging to the edge any way, it won't take much of a change to push them over."Original here