A United Nations monitoring trip to the Great Barrier Reef will land in Queensland later this month just as forecasts suggest the risk of widespread coral bleaching will be at its highest.
Unesco has confirmed two scientists will carry out the mission, requested by the Morrison government, lasting for 10 days from 21 March.
Forecasting from the US governments National Oceanic and Atmospheric Administration (Noaa) shows the visit could coincide with the reef being at risk of widespread bleaching.
Environment groups told the Guardian while they were not aware of any details of the itinerary, it was vital the scientists were allowed to see any bleaching for themselves.
The Great Barrier Reef Marine Park Authority reported late last week that low to moderate bleaching had already been reported in many areas.
The reef authority said significant heat stress had accumulated in some parts of the far north of the reef, as well as between Townsville and Rockhampton.
The Bureau of Meteorology is forecasting sea surface temperatures to remain above average throughout most of the marine park in the coming weeks, the authority said.
The 2,300km reef has seen five mass bleaching events in 1998, 2002, 2016, 2017 and 2020 all caused by rising ocean temperatures driven by global heating.
Corals can recover from mild bleaching if cooler conditions return quickly. Coral cover over the reef has risen in the last 18 months after benign conditions, but the Australian Institute of Marine Science has said this recovery is dominated by fast-growing corals susceptible to bleaching.
Dr William Skirving, of Noaas Coral Reef Watch, said the accumulation of heat stress had paused during most of February, but had now returned.
Without clouds and cooler weather, Skirving said there was a risk of bleaching from the Whitsundays to the northern tip of the reef by the last week of March.
But he said it was unclear how much the cloud cover in February had benefited the corals because the amount of sunlight, as well as the level of heat, were both important in translating the heat stress into bleaching.
The Morrison government requested the Unesco mission last year after it successfully lobbied against UN scientific advice that the reef should be placed on a list of world heritage sites in danger.
Unesco said the visit was confirmed by letter to the Australian government on 21 February, but there had been no official announcement of the visit.
One expert from Unesco and another from the International Union for Conservation of Nature (IUCN) would travel to the reef.
Unesco declined to provide any details about where the scientists would visit, as did the office of the environment minister, Sussan Ley.
A report from the mission is expected to be completed by early May ahead of a scheduled meeting of the 21-country world heritage committee in June.
The Morrison government has argued the reef is being singled out, and that world heritage sites should not be placed on the in danger list because of impacts from climate change.
The head of oceans at WWF Australia, Richard Leck, said Unesco advisers had last year recommended the reef be listed as in danger primarily because of concerns about the impacts of global heating.
It is absolutely vital that if there is a bleaching event, that these experts are witness to the impacts of coral bleaching, Leck said.
WWF fervently hopes there wont be a bleaching event, but if it does occur every effort should be made so that Unesco and IUCN are witness to that.
He said WWF Australia had made a formal request to the government to brief the mission while it was in the country.
We have also spoken directly to representatives of IUCN who are very keen to meet with non-governmental organisations, scientists and civil society, he said.
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Dr Lissa Schindler, a reef campaigner at the Australian Marine Conservation Society, said she expected an itinerary that ensured the visiting delegates gain a true picture of how seriously impacted our reef is by the climate crisis, water pollution and poor fishing practices, and what the solutions are.
Schindler said there had not yet been an invitation to non-government groups to speak with the mission, so we are concerned they will not be presented with a true picture of what is happening on our reef.
Prof Terry Hughes, a leading coral reef researcher at James Cook University, said the scientists should visit coalmines and export terminals along the reef to see for themselves the scale of fossil fuel exports across the reef.
They should look at the causes of the decline of the reef, he said.
The Guardian had reported that in the latest major UN climate report, the Morrison government unsuccessfully attempted to insert a sentence saying the reef was not in crisis.
A spokesperson for the environment minister said: The world heritage committee will be given every opportunity to satisfy its requirements.
The mission is being planned in collaboration with the world heritage centre and the International Union for the Conservation of Nature.
