NSW coal mine expansion fight reaches High Court in landmark climate emissions case

For the couple behind a coal mine expansion challenge that’s reached three levels of courts over four years, every fraction of a degree of warming matters.

The Upper Hunter Valley region where Wendy Wales and Tony Lonergan call home has already been see-sawing between drought, fires and floods.

Climate extremes are only expected to worsen as greenhouse gases from burning fossil fuels warm the planet further, prompting the pair to take the fight directly to the coal mines surrounding their farmland.

It’s now taken them to the highest domestic court, which is due to hear a case brought against the Mount Pleasant open-cut coal mine near Muswellbrook by a local environment group, headed by Ms Wales, on Wednesday.

The Denman Aberdeen Muswellbrook Scone Healthy Environment Group have been challenging operator MACH Energy Australia’s plan to double the mine’s output and keep it running out to 2048.

In July 2025, the NSW Court of Appeal ruled the mine’s approval was unlawful, and that planning authorities are legally required to consider the climate impact of scope three emissions - caused when the coal is eventually burnt, including overseas when exported - on local communities.

MACH Energy is now asking the High Court to overturn that ruling.

The mining company has prepared a case based on the validity of the Mount Pleasant extension’s approval.

“MACH Energy welcomes the opportunity to appear as an appellant to the High Court and will continue to operate in alignment with existing approvals and conditions and seek to provide long-term continuity and certainty for its staff, contractors, customers and the local community,” a spokesperson said on Tuesday.

Ms Wales said a decision in the community environment group’s favour could set a precedent and “turn a super tanker around”.

“We really we need all the wins we can get,” she told AAP.

“And this is a substantial one for providing courage to politicians, perhaps, that we’ve got more evidence and more reason to move away from export coal.”

The hearing will follow a landmark advisory opinion ruling by the International Court of Justice - the world’s highest court - that specified fossil fuel production could count towards the host country and constitute an “internationally wrongful act”.

Bond University professor of climate law Nicole Rogers said the opinion was not binding, meaning the High Court did not technically need to factor it into decision-making, but was still influential.

“Australia did play a role in supporting the request for the advisory opinion, so Australia can’t just say, ‘we’re washing our hands of that the advisory opinion, it has nothing to do with us’,” she told AAP.

Another key development was the growing acceptance of climate attribution science in similar legal proceedings, she said, to substantiate correlation between emissions from one particular source and particular climate impacts.

“Courts around the world - from The Hague to London to Canberra - are being asked the same fundamental questions: can legal systems keep pace with the climate crisis and to what extent are decision makers who continue to approve fossil fuel projects accountable for climate impacts?”