Global carbon emissions must be cut by at least 25 percent by 2020 to give the Great Barrier Reef a better chance of survival, an Australian reef and climate scientist revealed on Tuesday.

Representatives of the Federation of Australian Scientific and Technological Societies (FASTS) are in Canberra ahead of parliament's vote on the emissions trading scheme.

They also noted emissions would need to be cut by up to 90 percent below 2000 levels by 2050, if the reef is to survive the impacts of ocean temperature rises which contribute to coral bleaching and coral death.

"This is Australia's Great Barrier Reef and we must provide the leadership to help it survive," FASTS president Ken Baldwin told reporters.

More than 100 nations have endorsed a goal to limit average global warming to no more than 2 degrees above preindustrial temperatures, he said.

And that would need to be done by limiting the concentration of carbon dioxide to below 450 parts per million.

"To achieve concentrations below this value of 450 parts per million will require emissions reductions of at least 25 percent by 2020, so therefore to give the Great Barrier Reef a better than 50 percent chance of survival, emissions must be reduced by 25 percent," Baldwin said.