The scale of the second mass bleaching in two years won't be known for several weeks but early indications suggest the corals in the tourist heartland between Townsville and Port Douglas have been hammered.

Even as scientists from James Cook University and the reef's Marine Park Authority complete aerial surveys of the 2300-kilometre natural treasure, researchers such as Line Bay from the Australian Institute of Marine Science (AIMS) are returning from dives with grim tidings.

"We saw bleaching on every reef we went to," Bay tells me. "And it was quite significant", reaching as much as 90 per cent in shallow reefs.

Despite the imminent blow to their industry, tourism bodies are largely silent in calling for help for their prize asset.

Col McKenzie, who heads the Association of Marine Park Tourism Organisations, concedes the sector is reluctant to present a negative image that could turn off visitors.

"Farmers have 10 times our voice," he says, even though reef tourism alone probably keeps 70,000 people in jobs and generates about as much revenue - $6 billion a year - as mining for the Queensland.

For now, scientists aren't expecting the damage to reach last year's extent, when about 25 per cent of the reef's corals died. But that's hardly cause for celebration.

John Gunn, AIMS' chief executive, says scientists had forecast global warming to trigger the sorts of the bleaching seen this year and last, but not for another 10-15 years.

"It is now crisis time," Gunn tells me. "If you found a massive cancer clusters and cancer deaths, you've suddenly got to restart your thinking, and say well you've got to tackle this problem now."

But those looking for leadership at the federal or Queensland level are likely to be sorely disappointed. Attention, if anything, seems to be focused on making things worse.

Premier Annastacia Palaszczuk was busy leading a delegation to India last week, begging Adani to begin a monster coal mine that will - if the Galilee Basin as a whole gets developed - lead to billions of tonnes of extra greenhouse gases that are already cooking the reef.

Claims Galilee coal is cleaner than what India would otherwise burn are debatable but anyway miss the point: the great bulk of all fossil fuel deposits must stay in the ground if corals at home or abroad are to have much of a future.

Warren Entsch, the Liberal National Party member whose electorate takes in Cairns, tells me "we need a cyclone badly" to stir up the becalmed region and provide cooling cloud cover. (And he may get his wish, with weather models suggesting the season's first cyclone off Queensland may form early next week.)

However, he has no patience for "anti-fossil fuel campaigners" - such as former Greens leader Bob Brown, who on Wednesday launched the Stop Adani Alliance to block the new mine.

"The reef should not become collateral damage," Entsch told me last week. Even so, he also had little time for researchers such as Terry Hughes, a leading scientist who is conducting this week's aerial surveys of the reef and last week published a major paper on the 2016 and previous bleaching events.

"He'll be having an absolute ball," Entsch told me.

The reality is more than a few scientists rely on Hughes to get the message out that the reef is in serious trouble.

As if the threat from climate change - including more acidic oceans hindering corals to form skeletons at all - weren't enough.

Even where the federal and state governments are throwing money at the reef, such as trying to limit the Crown of Thorns starfish or reducing sediment and nutrient-rich run off from farms - the efforts are likely to be insufficient.

"There's a really, really major outbreak of the crown of thorns starfish in the same area off Townsville that is bleaching at the moment," Gunn says.

And, according to WWF Australia, farmers have told the Queensland government that they want to clear more than 270,000 hectares, more than half of which are in Great Barrier Reef catchments.

"It can only have dire impacts on the reef to have so much clearing promised," Martin Taylor of WWF says. "This is a ticking time bomb."

And we need some bomb defusers in a hurry.

Peter Hannam travelled to the reef as a guest of the Climate Council.