Once the jewel in Australia's crown, the Great Barrier Reef is fading.
The bleaching of the reef, caused by warmer sea temperatures, now affects up to .
Conservationists said bleaching has dire consequences for fish populations, which many developing countries rely on for food and livelihoods.
As Environment Minister Greg Hunt prepares to ratify the Paris agreement on Climate Change in New York on Friday night (22:30 AEST), there are calls for Australia to do more about the reef.
Speaking at a rally in Sydney on Friday, GetUp environment campaigner Sam Regester said urgent action was needed.
"The Great Barrier Reef is dying in front of our eyes," he said.
"Our government knew this was coming and they did nothing. While the rest of the world stands by and watches our coral and great barrier reef bleach, our government has been handing out billions of dollars in fossil fuel subsidies."
The Paris deal to slow climate change is set to be signed by more than 165 countries, including Australia.
It is the most number of states to endorse an international agreement on day one and backers hope this will inspire swift implementation.
Many states still need a parliamentary vote to formally approve the agreement. It will only enter into force when ratified by at least 55 nations representing 55 per cent of man-made greenhouse gas emissions.
UN Secretary-General Ban Ki-moon "wants to use the event to generate momentum around implementation and early entry into force of the Paris agreement", said Selwin Hart, director of Ban's climate change support team.
Some experts predict the 55 per cent thresholds can be reached this year. The UN said 13 countries, mostly small island developing states, are due to deposit instruments of ratification on Friday.
The UN expects about 60 heads of state and government at the signing ceremony. French President Francois Hollande and Hollywood actor and environmental activist Leonardo di Caprio are expected to attend.
China and the United States, the world's top emitters accounting together for 38 per cent of emissions, are due to sign, along with Russia and India, who round out the top four.
Many developing nations are pushing to ensure the climate deal comes into force this year, partly to lock in the US if a Republican opponent of the pact is elected president in November.
Even if the pact is fully implemented, promised greenhouse gas cuts are insufficient to limit warming to an agreed maximum, the United Nations says.
The first three months of 2016 have broken temperature records and 2015 was the warmest year since records began in the 19th century, with heat waves, droughts and rising sea levels.
Warm waters have done widespread damage to corals in Australia's Great Barrier Reef, and sea ice in the Arctic hit a record winter low last month.
"The magnitude of the changes has been a surprise even for veteran climate scientists," said Petteri Taalas, secretary-general of the World Meteorological Organisation.
Australia will be represented by Environment Minister Greg Hunt. Environmental activists are calling for greater action from Canberra after extensive surveying of the Great Barrier Reef found 93 per cent of the 2300km-long natural wonder has been affected by coral bleaching as a result of warmer ocean temperatures.
