An international line-up of actors, conservationists and scientists, including Joanna Lumley and Hollywood star Jason Momoa, has backed calls for the Great Barrier Reef to be placed on a list of world heritage sites in danger. “The scientific evidence is beyond doubt: the Great Barrier Reef is in danger and it is time to act,” the group said in a global statement released to Guardian Australia. Later this week the 21-country world heritage committee will be asked to put the world’s biggest reef system on its danger list after global heating caused mass coral bleaching in 2016, 2017 and 2020. “There is still time to save the Great Barrier Reef, but Australia and the world must act now,” the statement says, backing a recommendation from the UN’s science and culture agency. “We commend Unesco for its leadership. We urge the world heritage committee to endorse Unesco’s recommendation.” Signatories include actor and activist Lumley, Aquaman actor Momoa, Prince Albert of Monaco, Australian singer Cody Simpson, former lead UN climate negotiator Christiana Figueres, and British endurance swimmer and UN patron of the oceans Lewis Pugh. The Australian government launched a fierce lobbying effort to block the listing after Unesco made the recommendation last month. Australia’s environment minister, Sussan Ley, has been in Europe for more than a week to lobby countries against the danger listing. At the same time, Canberra-based diplomats from 13 countries and the EU flew to the Great Barrier Reef, off the Queensland coast, for a snorkelling trip on Thursday hosted by the Australian government. The Scott Morrison government is arguing Unesco should have carried out a monitoring mission before making its recommendation, and has said the decision was political. Unesco says no rules were broken and its recommendation was based on scientific reports from the government’s own agencies. The statement was organised by the Australian Marine Conservation Society. The group’s chief executive, Darren Kindleysides, said: “The influential individuals who have signed up to this statement are from all over the world, showing that adoration and alarm for our reef is not just a concern for Australians. “The reef belongs to the world and, as its custodian, Australia must show global leadership on climate action to preserve its future.” Other signatories include American ocean explorer Sylvia Earle, British author and marine scientist Prof Callum Roberts and oceanographer Philippe Cousteau, the grandson of French diving pioneer Jacques Cousteau. Middle eastern countries Bahrain and oil-rich Saudi Arabia have agreed to back Australia and have tabled amendments asking the committee, chaired by China, to push the decision back to at least 2023. The 2,300 km (1,430 mile) Great Barrier Reef has been on the world heritage list – which identifies places of significance to humanity – since 1981. On Monday, the government’s Australian Institute of Marine Science said the reef had been through a benign 12 months, but new corals growing were a species that would be quickly wiped out by ocean heatwaves, storms and coral-eating starfish. “The predicted consequences of climate change, which include more frequent and intense mass coral bleaching events, are now a contemporary reality,” the report said. Coral reefs are considered one of the world’s most at-risk ecosystems from the climate crisis due to their sensitivity to warming oceans. No world heritage site has ever been placed on the “in danger” list explicitly because of impacts from global heating. Unesco is also asking Australia to link its policy to protect the reef to the Paris climate goals to keep heating to 1.5C. Australia has one of the highest per capita levels of greenhouse gas emissions in the world, and is also one of the world’s biggest exporters of coal and liquified gas.