A study published today in Environmental Science and Technology Letters found that methane emissions from an open-cut coal mine in Queensland's Bowen Basin were up to eight times higher than the operator's reported annual average for the 2023 financial year (FY2023).
UNSW Sydney researchers were part of an international team led by the United Nations Environment Programme's International Methane Emissions Observatory (UNEP's IMEO). The team studied methane plumes via two different instruments attached to research aircraft. They flew over the Hail Creek open-cut coal mine in September 2023, comparing observed measurements downwind of the mine to operator-reported emissions.
Their results showed that, if sustained throughout the year, the methane emissions from the mine could be three to eight times higher than what the operator reported for FY2023.
The study is the first to successfully verify reported emissions from an open-cut coal mine in Australia using this method. The results highlight the need for continued independent verification, as well as a refinement of the current methods used to estimate emissions.
"Our airborne measurements are further evidence that emissions from the mine are not well-captured using state-wide emission factors," says UNSW co-author Dr Stephen Harris from the UNSW ESSRC Greenhouse Gas (GHG) Measurement team.
"The results support phasing out these generic reporting methods in favour of more advanced, mine-specific coal gas content modelling for open-cut coal mines in Australia."
Measurements vs estimations
Methane is a gas more than 80 times more damaging to the climate over 20 years than carbon dioxide. Australia signed the Global Methane Pledge in 2022, joining more than 150 countries in a pledge to reduce global methane emissions by at least 30% below 2020 levels by 2030.
Coal mines account for around one-third of overall fossil fuel methane emissions. Governments and industries across the world are now seeking better methods to accurately estimate their methane inventories, particularly in the open-cut coal mining sector, as robust verification methods are not common.
UNEP's IMEO conducts studies to equip policymakers and industry with the insights they need to better track – and ultimately mitigate – emissions. The airborne method used in this study is an approach that can be used to verify the emissions data reported under the National Greenhouse and Energy Reporting (NGER) framework from Australian coal mines.
Hail Creek's reports during FY2023 were based on state-wide emission factors. These are not actual measurements but instead are estimates: calculations based on how much coal is extracted and used. The study coincides with the Australian government's decision to phase out these factors when estimating fugitive methane emissions from open-cut coal mines.
"Atmospheric chemistry observations recorded using aircraft- or satellite-based platforms, as well as other ground-based monitoring systems, are important for quantifying the true emissions from coal mines," says Dr Harris.
"These data highlight the potential for the coal sector to measure, verify and mitigate its methane emissions," he says.
"Reducing methane emissions is a fast, cost-effective way to slow global warming in the near-term."
The significance for steel production
The Bowen Basin, where the Hail Creek mine is located, is home to nearly all of Australia's metallurgical coal – aka met coal – which is used in steel production. Met coal is an often-overlooked opportunity to make quick and affordable progress in fighting climate change, the researchers say.
According to IMEO, the methane released from met coal extraction contributes to about a quarter of steel's climate impact. They say better management of fugitive methane emissions could be achieved at just 1% of the cost of making steel.
"There is so much potential for the steel supply chain to step up, rein in its methane emissions, and have a real impact on climate in the coming years," says Manfredi Caltagirone, Head of IMEO.
But to do this, they need to know where the methane is and how much of it is there.
"We need better, verified data like those in this study to seize this mitigation opportunity," Mr Caltagirone says.
Where to now?
"This case study highlights how atmospheric chemistry observations can guide the refinement of current coal-core-based methods for estimating methane emissions from open-cut coal mining," says UNSW Associate Professor Bryce Kelly from the UNSW ESSRC Greenhouse Gas (GHG) Measurement team.
A/Prof. Kelly has mapped methane emissions throughout Australia since 2014. He says over this time it has become clear that aircraft-based methods can serve as an essential tool for verifying reported methane emissions.
"We need precise, reliable data to guide efforts to curb atmospheric pollution and slow climate change," he says.
"This IMEO study has demonstrated a robust approach that can be used throughout Australia to identify reporting anomalies as well as mitigation opportunities."
Key Facts:
UNSW researchers say a Queensland coal mine – previously identified by satellites as one of the state's highest methane emitters – could be releasing greenhouse gases at higher rates than officially reported.
