Professor Stephen Williams is taking me through a locked gate, up a mountain, to one of the most extraordinary places in Australia.

The cloud forests of the Wet Tropics World Heritage Area in Far North Queensland are some of the wettest places in the country.

As the name suggests, the mountain summits are almost perpetually shrouded in cloud. But as the sea breezes create gaps in the fog, the rainforest reveals itself.

"This place is just so special," says Professor Williams, who has spent his whole career studying the wildlife here.

"It's made a world heritage area because there are so many unique species here that occur nowhere else. They're here on this mountain and nowhere else."

Professor Stephen Williams has spent his career studying the wildlife of the Wet Tropics World Heritage Area in Far North Queensland. ( ABC: Ben Deacon )

The Wet Tropics World Heritage Area covers a tenth of 1 per cent of Australia's land mass, yet contains 50 per cent of all the nation's species. It's the definition of a biodiversity hot spot.

Record heatwave puts species at risk

Professor Williams and I are here to look for a creature called the white lemuroid possum. The white lemuroid possum is a rare variety of lemuroid possum, which only lives in two populations high in the Wet Tropics World Heritage Area. Both populations are at risk.

The white possum was nearly wiped out in the Mount Lewis region by a heatwave in 2005.

"After that time, we didn't see any lemuroids for seven years so the heatwave had knocked the population down to such a low level we couldn't find them spotlighting, using exactly the same methods where previously we'd seen lots of them," Professor Williams recalls.

"They started to recover, and after about seven years we started to see an occasional lemuroid, and then a couple and then four, so they were slowly recovering. Of course, that's until the next heatwave."

The Wet Tropics World Heritage Area contains 50 per cent of all the nation's species. ( ABC: Ben Deacon )

That heatwave came in late November last year, when the Cairns region was hit by the highest temperatures since records began.

"It scared the pants off me basically. One of the rangers sent me some data from the highest mountain in the wet tropics, where it got up to 39 degrees, which is off the charts."

Professor Williams's work has shown many tropical species just can't handle extreme heat.

"They haven't evolved mechanisms to cool their bodies down," he says.

"They don't sweat, they don't pant, they don't have a way to keep cool. And they've never had to."

"It just takes a couple of days, these possums die from temperatures above 29 degrees, after about 5 hours."

'Things have started to disappear from the lower elevations'

The ringtail possum is also a resident of the Wet Tropics World Heritage Area. ( Supplied: Wet Tropics Authority )

After dark, Professor Williams and I head out spotlighting. Biologists estimate population trends of rainforest animals by searching the same areas, year after year.

Professor Williams now has more than 15 years of data from a range of sites around the Wet Tropics World Heritage Area. He says the trend is clear.

"What we've noticed over the past 15 years is systematically things have started to disappear from the lower elevations," he says.

"Ringtail possums, we used to see at 600 metres. Twelve years ago, they disappeared from there. We'd still see them at 700 metres. Eight years ago, they disappeared at 700 metres. We're still seeing them now at 800 metres, and basically, it's the same with the birds.

"We've systematically seen species disappear at the low elevations and be pushed up the mountain. Which means the total populations are declining because they're being pushed and pushed into a smaller and smaller area."

We're spotlighting near the summit of Mount Lewis. A headlamp catches the flash of a pair of tiny eyes halfway up a tree.

"It's a Daintree River ringtail," Professor Williams says.

"It used to be common at about 1,000 meters, now it's common at 1,200 metres."

The Wet Tropics World Heritage Area is one of the wettest places in the country. ( ABC: Ben Deacon )

As new species migrate to higher elevations it spells trouble for the creatures, like the white possum, that call the mountain summits home.

"They've just got nowhere else to go. There's no rainforest south that they can move to. The nearest rainforest is a thousand kilometres away."

Climatologist Andrew King says northern Australia is seeing more heatwaves, longer heatwaves and more intense heatwaves due to human-caused climate change.

"We're seeing a lot more records broken now than we used to," Dr King says.

"In the first part of this century we're seeing 12 times as many hot records as cold records in Australia."

Professor Williams and I end the night without finding a white lemuroid possum. Soon the rain starts, as the monsoon hits the cloud forests of Queensland's far north.