High Court Rejects Mount Pleasant Coal Expansion Over Overseas Emissions
Australia's High Court dismissed MACH Energy's appeal over the Mount Pleasant coalmine expansion in a 3-2 ruling on 7 October 2026, keeping the project's rejection in place The Guardian.
The majority upheld the NSW Court of Appeal's unanimous 2025 decision. That decision had overturned approval for the expansion at Muswellbrook in the Hunter Valley. It had reversed an earlier judgment of the NSW Land and Environment Court, which had ruled for MACH Energy after a challenge by the Denman Aberdeen Muswellbrook Scone Healthy Environment Group.
At issue was the assessment duty of the NSW Independent Planning Commission, the body that decides major projects. The High Court majority found the Commission was required to consider how to mitigate greenhouse gas emissions from coal sold and burned overseas, and had failed to do so. It also found the Commission had failed to consider conditions to minimise those downstream emissions, known as Scope 3 emissions, to the greatest extent possible.
The project is the Mount Pleasant Optimisation Project. MACH Energy owns the existing open-cut Mount Pleasant Coal Mine in the Upper Hunter Valley. It proposed to double output from the currently permitted 10.5 million tonnes per annum to 21 million tonnes per annum, and to extend operations to 2048. The current permission runs to December 2026. If built as proposed, it would be one of the largest open-cut projects in New South Wales. About 98% of its projected emissions are Scope 3 emissions.
The path to this point was long. The Commission approved the expansion in 2022. The community group, led by president Wendy Wales, challenged that approval. It lost in the Land and Environment Court but won unanimously in the Court of Appeal in 2025. MACH Energy then appealed to the High Court. The case is listed as MACH Energy Australia Pty Ltd v Denman Aberdeen Muswellbrook Scone Healthy Environment Group Inc & Anor (S174/2025) High Court. It was the first time the High Court was asked to consider a case on climate grounds.
The broader context here is how the law treats exported emissions. The majority did not prohibit coal mining. It did not rule that Scope 3 emissions must block approval. It ruled on process. A decision-maker must address mitigation and whether conditions could reduce downstream emissions where the law requires it. For planners and lawyers, the focus shifts from whether overseas burning can be counted to how authorities record their thinking on mitigation.
Looking at what this means for planning in New South Wales, the decision narrows room for approvals that treat Scope 3 emissions as beyond conditioning. Future applicants and the Commission will need to show active consideration of feasible conditions, even where supply chains are complex and burning happens outside Australia. Opponents now have a clearer template for judicial review based on failure to consider, rather than on climate policy itself. The ruling leaves open how far such conditions can practicably go, and how courts will judge cases where authorities consider mitigation but decide not to impose it.
