New research shows global warming of 1.5C will be catastrophic for almost all coral reefs worldwide, even sites scientists once thought of as refuges.
The study is a dramatic escalation in expected outcomes and sobering news for economies like Australia that rely on reefs to support key industries including fishing and tourism.
James Cook University Associate Professor Scott Heron was part of the international study and says previous analyses pointed to about 90 per cent of global reefs being affected at 1.5C of warming.
Under that scenario, about 10 per cent of the world's reefs would have escaped frequent warming impacts via natural mechanisms like the consistent upwelling of cool, deep waters.
But the new analysis suggests it will be nothing like 10 per cent, more like 0.2 per cent.
"We are now looking at one fifth of one per cent of coral reef locations avoiding those frequent heat stress impacts," Dr Heron says.
"Our study has indicated that the situation global coral reefs are facing is even more dire than we'd previously thought and it's all related to climate change."
The most authoritative body on climate science, the Intergovernmental Panel on Climate Change (IPCC), has already warned the world is off course and won't limit warming to 1.5C unless it redoubles efforts to slash emissions.
On the current trajectory, the planet is likely to hit 1.5C of warming by about 2030. Even with radical action to cut emissions, warming is still likely to reach 1.6C before falling back again.
Dr Heron says the study is yet more evidence of the pressing need for immediate action to curb greenhouse gas emissions.
"We need to have changes happening in our energy policies this decade," he said. "We also need to ramp up local actions to help reefs survive through already predicted impacts.
"There's as many as one billion people around the world that rely upon the coral reef ecosystems for part of their sustenance or livelihoods. Australia is one of those countries, Australians are some of those people."
Scientists involved in the study used the latest IPCC projections and modelled likely outcomes for shallow-water coral reefs around the globe.
Scientists found there were a small number of "hope sites" that might persist at 1.5C. But that was because they are in areas that already have high temperature variability, meaning corals might be better equipped to cope with the impacts of warming.
As far as Dr Heron is aware, none of them are in Australian waters.
