Scientists fear climate change has already caused a mass die-off among the species, which lives in only two pockets of high-altitude rainforest in the Wet Tropics World Heritage area near Cairns, in Far North Queensland.

''We haven't seen lemuroids at one of these two sites for the past three years,'' the director of James Cook University's Centre for Tropical Biodiversity, Steve Williams, said.

''We used to see one around every 45 minutes when we were doing spotlight surveys on Mt Lewis.''

''We cannot say they are extinct, but all the signs point to the species being in very serious trouble.''

Climate change has diminished the nitrogen and water content of leaves eaten by the possums, increasing their vulnerability to heat stress.

Research shows the possums need to eat more leaves to obtain enough protein and water, but the leaves also contain protective toxins that restrict the quantity of leaves the animals can eat.

In a paper published in 2003 in the internationally published journal Science, DrWilliams warned more than 70 of Australia's tropical rainforest species faced extinction if temperatures increased by one degree.

''Lemuroids don't pant, sweat or come down from the trees to drink. It's been estimated around four to five hours of temperatures above 30 degrees will kill an animal,'' he said.

'' If you had a day where temperatures were above 30 degrees for eight hours, it would be enough to wipe out the entire species.''

The possum, which has two colour forms white and chocolate brown is listed as globally threatened in the 2008 Red List issued last month by the International Union for the Conservation of Nature.

Although the brown lemuroids have been known to science since 1884, the much rarer white lemuroids which are not albinos were discovered by Queensland parks staff only in the 1980s, during protests to save Mt Lewis from logging.

A federal action plan to protect the possum has lapsed, and it is not listed as a species at risk under the Environment Protection and Biodiversity Conservation Act.

The action plan, which runs to just over a page of nine dot points, was not updated since it was published in 1996, despite more than a decade of scientific research specifying the risks of climate change.

According to advice provided by the Department of Environment, the possum would need to be nominated for protection under federal law by next March.

Its status would then be assessed by the department's threatened species committee, who would advise Federal Environment minister Peter Garrett whether the species should be formally listed as threatened.

Greens biodiversity spokeswoman Senator Rachel Siewert said the situation highlighted the failure of the Act to protect Australia's endangered species.

''It is quite bizarre that a native species at such a high risk of extinction from climate change should not be protected. It shows exactly why we are currently conducting a Senate inquiry into the failings of the Act.''