The long-term outlook for Australia's Great Barrier Reef was downgraded to "very poor" for the first time Friday by the official agency charged with managing the world heritage site.
In its latest five-yearly report on the health of the world's largest coral reef, the Great Barrier Reef Marine Park Authority singled out rising sea temperatures due to climate change as the biggest threat to the giant organism.
"The significant and large-scale impacts from record-breaking sea surface temperatures have resulted in coral reef habitat transitioning from poor to very poor condition," the government agency said.
It said "strong and effective management actions are urgent at global, regional and local scales" to rescue the 2,300-kilometre (1,400-mile) reef, a UNESCO World Heritage site.
"The Reef is core to Australia's identity and improving its outlook is critical," it said, adding that in addition to countering climate change, further action was needed to halt the run-off of agricultural pollutants into reef areas.
"The window of opportunity to improve the reef's long-term future is now," it said.
The conservative Australian government has faced criticism from environmentalists for favouring an expansion of its massive coal mining and export industry over action to curb climate change.
Friday's reef report coincided with the release of new government data showing that Australia's emissions of greenhouse gases blamed for climate change continued a four-year rising trend during the first half of 2019.
The government insists it is nevertheless meeting its emissions targets as set under international protocols, including the Paris climate agreement, and argues that Australia's total greenhouse gas output remains far below that of major polluting nations.
"This report calls out climate change as the biggest threat to the reef," Environment Minister Sussan Ley acknowledged at the release of the outlook report.
But she added: "We are taking the action that we're required to do under our Paris agreements."
Environmentalists said the latest reef outlook put new pressure on Prime Minister Scott Morrison over his support for expanding production of coal, Australia's biggest export.
"Australia must do its fair share in the global effort to tackle climate pollution. That means moving on from digging up and burning coal and gas for our energy," said Kelly O'Shanassy, CEO of the Australian Conservation Foundation.
The United Nations had asked to receive the latest update on the reef's health by December so that it can determine whether the site can retain its world heritage status when UNESCO next considers the issue in 2020.