A leading coral reef scientist says the world's industrialised nations need to cut carbon emissions by up to 90 per cent by 2050 or risk losing the Great Barrier Reef off Queensland.

Professor Terry Hughes from James Cook University, along with 13 other marine and environmental scientists, delivered a briefing in Parliament House this morning.

Professor Hughes told the gathering, the Great Barrier Reef contributes $5.4 billion annually to the Australian economy.

"The response was mixed depending on the political persuasion of individual politicians but I think that everyone realises that there's a problem," he said.

"Everyone is aware of the threats to the Great Barrier Reef, to other ecosystems through the land, fires on land, so the debate is about how we get to those targets."

He says even a slight increase in average temperatures could cause massive coral bleaching on the reef.