A new report has valued Australia’s Great Barrier Reef at $56 billion, more than double the value of a new coal mine opponents claim will help kill it.

The World Heritage-listed asset underpins 64,000 direct and indirect jobs, and contributes $6.4 billion to the nation's economy each year, according to the report produced for the Great Barrier Reef Foundation.

The $56 billion price tag is equivalent to 12 Sydney Opera Houses, five new national rail programs and more than four times the length of the Great Wall of China in $100 notes.

By comparison, Adani's planned Carmichael coal mine project and its associated infrastructure has been valued at $21.7 billion, with the Indian miner forecasting 10,000 direct and indirect jobs.

The mine is also expected to generate $203 million in direct and indirect contributions during construction and $274 million in production.

Asked how the federal government could support the mine, when the value of the reef dwarfed it, Environment Minister Josh Frydenberg said Australia's coal was "cleaner than other sources".

The Great Barrier Reef as viewed from above last year. (AAP)

"If Australia vacates this field, not only will we be forgoing billions of dollars' worth of export income and thousands of jobs domestically, but somebody else will sell that coal into India and the impact on the environment could be worse in terms of emissions," Mr Frydenberg said in a statement today.

The Australian Conservation Foundation (ACF) said emissions from the coal Adani will mine will fuel the primary threat to the reef's survival: climate change.

"It's just a disturbing statement to hear from our federal environment minister," ACF campaigner Basha Stasak said.

"Our governments seem to refuse to acknowledge the reality of the situation. It's a choice - it's coal or it's coral and we are going to have to pick."

The United Nations Agency UNESCO has said that "climate change remains the most significant overall threat to the future" of the coral expanse. (AAP file image)

A former chief scientist of the Australian Institute of Marine Science, Charlie Veron, last week urged the Turnbull government to revoke Adani's environmental approval, saying coal mining was the primary threat to coral reefs worldwide.

"If we wipe out coral reefs, we are going to crash the ecologies of the oceans," he told ABC News.

Climate scientist Professor Will Steffen, from the Climate Council, echoed that call.

"We're gambling with this priceless global asset if we persevere with any new fossil fuel developments - and there's no room for exceptions here," Mr Steffen said.

Greenpeace said it was impossible to put a dollar value on a global wonder, and the Deloitte report missed the point.

Bleaching damage on the Great Barrier Reef in April 2017. (AAP)

"We have an inescapable moral responsibility to save it for us, and for future generations - regardless of its economic value," climate and energy campaign director Nikola Casule said.

The reef has suffered back-to-back mass coral bleaching events due to warming ocean temperatures.

Earlier this month, UNESCO expressed serious concern about the bleaching, saying climate change remained the most significant threat, and urged Australia to work faster to improve water quality.

The Deloitte report said that of the 64,000 jobs linked to the reef, 39,000 were direct jobs - making the reef a bigger "employer" than the likes of Telstra, the Qantas Group, National Australia Bank, and the oil and gas extraction industry.

With AAP