The world's reefs, including Australia's Great Barrier Reef, will be dead within 30 years unless human activity changes quickly, a leading researcher says.
Addressing the 11th international Riversymposium in Brisbane, Professor Ove Hoegh-Guldberg said it was crunch time for the world's reefs.
"Let's say we delay another 10 years on having stern actions on emissions at a global level, we will not have coral reefs in about 30 to 50 years," he said.
Prof Hoegh-Guldberg, from the Centre for Marine Studies at the University of Queensland, said rising CO2 levels and melting ice caps meant the ocean was becoming uninhabitable for reefs.
This worldwide change in climatic conditions was in addition to land-based pollution spilling from Queensland's coastal river systems, a symposium session into the impacts of river systems on the reef was told.
"We're rapidly rising to (CO2) levels which will be unsustainable for reefs in the very near future," Prof Hoegh-Guldberg said.
"If you ask the question, `Will we have coral reefs in 30 years' time?', I would say at the current rate of change and what we're doing to them, we won't. But it's all up to us right now.
"We're at the fork in the road. If we take one road - the one we're on right now - we won't have coral reefs.
"If we make some very, very, very aggressive actions, if we reform how we do things, both at the global and local level, we'll have a really good chance of bringing coral reefs through in some shape or form, which will still provide the basis for the 100 million people that they support."
He said ice core samples showed CO2 levels were the highest for at least a million years, possibly 20 million years.
"That changes the circumstances under which corals form their skeletons, so they become less vibrant," Prof Hoegh-Guldberg said.
"Then if you keep hitting them with things like bleaching events, they just don't bounce back as much.
"So we're changing essentially the rules under which biology is trying to operate, and that's the problem."
He also warned that an increasing incidence of coral bleaching was a growing threat.
"If we have them (bleaching events) now every four to five years, we're getting to a point where reefs no longer have time to recover."
The impact on Queensland's $6 billion-a-year earnings from reef-based tourism would be enormous, he said.
"So we might have an industry that's half the size, but it certainly won't have the pull that it does today," he said.
