In the heart of what appears to be a pristine national park, a greenhouse gas is leaking out of an underground coal mine more than 30 years after it was last used.
Thermal vision filmed by the Australian Conservation Foundation (ACF) this year, and given to the ABC, shows methane coming from old mine vent shafts in the Dharawal National Park, south of Sydney.
Operations at North Cliff, which is part of the South32-owned Appin Mine, ceased in 1990.
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According to the United Nations, methane is a "powerful" greenhouse gas responsible for approximately a quarter of global warming to date.
It traps more heat in the atmosphere than carbon dioxide (CO2), and is 80 times more harmful than CO2 for 20 years after its release.
Methane emissions contribute to almost 30 per cent of Australia's total emissions and reducing them is vital to tackling climate change.
While the agriculture sector is the biggest emitter of methane, the energy sector is the second biggest contributor with coal mines considered the worst.
When coal seams are disturbed through mining activity, trapped gases known as fugitive emissions are released into the atmosphere.
Research from the US Department of Energy shows methane can continue to leak for decades after mining has stopped.
Conditions 'flouted for more than 30 years'
Tom Kristensen and Deidre Stuart live in the Illawarra region and are concerned about the mine's ongoing impact on the environment, saying in addition to climate change the methane poses a fire threat to the national park.
Their group Protect Our Water Catchment (POWC) enlisted not-for-profit legal centre the Environmental Defenders Office (EDO), to help pressure both South32 and the state government to have the site rehabilitated.
The EDO has asked government regulators to force South32 to comply with its rehabilitation requirements, and to pursue the company for the maximum penalty, which is up to $1.1 million per offence.
"We're worried that miners just tend to move off from their responsibilities once they've finished making money off the site," POWC president Tom Kristensen said.
The NSW government said "it is a requirement that rehabilitation is undertaken as soon as reasonably practicable".
Ms Stuart said the government needed to started enforcing the rules.
"This company had conditions attached to its approval and they've flouted them for more than 30 years," she said.
South32 said it was "aware that some residual methane is emitted from the shafts" that were sealed with concrete in 2005 for safety purposes when it was owned by BHP.
It said a rehabilitation plan had been submitted to the state government "which is intended to prevent residual emissions".
South32 is negotiating to sell Illawarra Metallurgical Coal, its company which runs the Appin Mine including the North Cliff shafts.
It said once the transaction was complete "all associated assets and liabilities will be transferred" to Golden Energy and Resources and M Resources, a consortium including businesses in Singapore, Indonesia and Australia.
That means all rehabilitation requirements will be passed on to the new owner.
Claims Australia failing to accurately report
ACF scientist Piper Rollins said the South32 mine site was an example of a broader regulatory failing when it came to methane.
"There's countless sites just like this one, all across Australia, which means that decommissioned and unrehabilitated mines could be playing a much more substantial role than we think," Ms Rollins said.
A 2021 State of the Environment Report said Australia had more than 50,000 abandoned mines, "most of which are decades old and may not meet modern rehabilitation and closure standards".
"We're in a situation in Australia where we have coal mines that could be emitting gas for up to 40 years after they've stopped mining coal," Ms Rollins said.
Under Australia's current reporting rules, emissions from open cut mines and decommissioned mines can be estimated.
For example, other ACF investigations found a NSW underground coal mine that shut in 2014 emitted the methane equivalent of more than 1 million tonnes of CO2, while a Queensland open-cut mine emitted more than a year's worth of its reported emissions in just 16 days.
EDO lawyer Kirsty Ruddock said governments needed to force mine operators to rehabilitate.
"We know that a number of mines both in NSW and Queensland will be either reducing their operations or closing due to demands for coal going forward," Ms Ruddock said.
"It's really important that the government is responsibly regulating this matter and on top of that so that those costs are not passed onto them ultimately and those mines are bearing those costs."
International Energy Agency (IEA) data from March shows Australia could be under-reporting its methane emissions by the fossil fuel sector to the United Nations Framework Convention on Climate Change (UNFCCC) by at least 64 per cent.
IEA's Global Methane Tracker estimated there were more than 1.6 million tonnes during 2022, despite Australia reporting just 1 million tonnes to the UNFCCC.
Technology reveals more than reports
Satellite and thermal imaging technology have helped shed light on the scale of methane emissions and reduced the reliance on industry reports.
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Independent MP for Warringah, Zali Steggall, said the gap between what is being reported and what is being emitted is so large it could undermine Australia's Paris Climate commitment to help limit global temperature increases to 1.5 degrees Celsius.
"I am pressuring the government to ensure we do our bit otherwise Australia is misleading the international community," Ms Steggall said.
Late last year Australia signed up the UN's Global Methane Pledge, which regards rapidly reducing methane emissions from energy, agriculture, and waste as "the single most effective strategy to keep the goal of limiting warming to 1.5C".
A review of the National Greenhouse and Energy Reporting Scheme by the Climate Change Authority (CCA) published in December made several recommendations to improve "the accuracy of estimated fugitive methane emissions".
The CCA suggested improved satellite-based monitoring programs would better detect fugitive emissions from Australian facilities.
The federal government's climate change department said it was considering those recommendations and working with stakeholders to implement some initial changes to the scheme "including on the estimation of fugitive emissions from open-cut coal mines".
South32 has been working with the CSIRO at the Appin mine to develop methane capture technology to turn it into CO2 since 2013 and received a $15 million NSW government grant in 2022.
But more than a decade since the project began, it has not progressed past pilots and trials.
