Australia's top Great Barrier Reef officials warn the natural wonder will virtually collapse if the planet becomes 1.5 degrees hotter – a threshold that scientists say requires shutting down coal within three decades.
This federal election campaign is a potential tipping point for Australia's direction on climate action, as the major parties pledge distinctly different targets for cutting greenhouse gas emissions.
However neither party has rejected the proposed Adani mine outright or promised to phase out coal, an export on which Australia is heavily reliant.
Climate change has already wrought devastating effects on the World Heritage-listed Great Barrier Reef, including two consecutive years of mass coral bleaching in 2016 and 2017.
In response to the threat, the Great Barrier Reef Marine Park Authority – the federal government's lead agency for managing the reef – has prepared a climate change position statement.
The document, obtained by the Sydney Morning Herald and The Age under freedom of information laws, has not been released to the general public despite being in development for the past 15 months.
It states that limiting the average global temperature increase to 1.5 degrees or below since industrial times began – the more ambitious end of the Paris agreement target – "is critical to maintain the ecological function of the Great Barrier Reef". The world has already warmed by 1 degree.
Ecological function refers to roles performed by the reef's plants, animals and habitats, including providing a tourist experience. The authority has said these processes are necessary for the reef to exist.
The document cites scientific evidence that the reef could experience temperature-induced bleaching events twice per decade by about 2020 and annually by 2050 under high-emissions scenarios.
The authority has long said climate change is the greatest threat facing the reef. However climate action advocates say to date, it has not sufficiently emphasised the repercussions of exceeding a 1.5-degree temperature rise.
A report prepared by the United Nations' Intergovernmental Panel on Climate Change in October last year said it was possible to keep warming below 1.5 degrees, but only with "rapid, far-reaching and unprecedented changes in all aspects of society".
This included phasing out coal-generated electricity globally by 2050, unless unproven technology to capture carbon dioxide from coal plants was deployed.
The Morrison government has pledged to cut Australia's emissions by 26 per cent by 2030, based on 2005 levels. Experts say the target is not in line with keeping global warming below even 2 degrees.
The government has been plagued by internal divisions over emissions and insists coal has a strong future in Australia.
It has backed the controversial Adani mine and is considering underwriting new coal-fired generation projects in a bid to boost energy reliability and affordability.
By 2030, Labor wants half of Australia's electricity needs met from renewable sources and a 45 per cent cut to national emissions. It says a transition away from coal is inevitable, but has no plans to shut down the industry. It has expressed scepticism about the Adani mine's future but has not pledged to stop it if Labor wins government.
The Greens say that by 2030, thermal coal exports and coal burning in Australia should cease.
WWF-Australia head of oceans Richard Leck said the reef authority's explicit recognition of the need to stay below 1.5 degrees of warming was a "long time coming".