This is the grim warning by some of the world's foremost marine and environmental scientists who briefed MPs in Canberra.

“The 'outstanding universal values' of the GBR (Great Barrier Reef), recognised by its inclusion on the World Heritage List in 1981, are now threatened by rapid climate change,” said Terry Hughes, director of ARC Centre of Excellence for Coral Reef Studies at James Cook University.

“Coral reefs are in the front line of the effects of climate change because of their sensitivity to both relatively small temperature rises and to acidification of the oceans due to increased levels of dissolved CO2," said Western Australian Premier's Fellow and professor Malcolm McCulloch.

To date, atmospheric caron dioxide (CO2) has risen to 390 parts per million, resulting in an increase in temperature of 0.7 degrees Celsius and a rise in ocean acidity, said an ARC release.

"Unprecedented coral bleaching and extensive mortality due to thermal stress affected over 50 percent of the GBR in 1998 and 2002, when summer maximum water temperatures were elevated by only 1-2 degrees Celsius. Some parts of the GBR have still not fully recovered,” said Ove Hoegh-Guldberg, professor at the ARC Centre.

“Ocean acidification will impact all marine calcifying organisms, potentially disrupting the entire ecology of the world's oceans, resulting in severe socio-economic impacts on fisheries and other marine industries,” said Hoegh-Guldberg.