High Court Upholds Rejection of Mount Pleasant Expansion Over Scope 3 Emissions
Australia's High Court dismissed MACH Energy's appeal over the proposed Mount Pleasant coalmine expansion in a 3-2 ruling on 7 October 2026, leaving in place the New South Wales Court of Appeal's rejection of the project The Guardian.
The vote was 3-2. The majority upheld the Court of Appeal's unanimous 2025 decision, which had overturned approval for the expansion at Muswellbrook in the Hunter Valley. That appellate ruling had reversed an earlier judgment of the NSW Land and Environment Court, which had found in favour of MACH Energy after a challenge brought by the Denman Aberdeen Muswellbrook Scone Healthy Environment Group.
At issue was the scope of the NSW Independent Planning Commission's assessment duty. The High Court majority found the Commission was required to consider, and had failed to consider, how to mitigate greenhouse gas emissions from coal that would be sold and burnt overseas. It further found the Commission had failed to consider imposing conditions to minimise Scope 3 emissions to the greatest extent possible.
The project at stake is the Mount Pleasant Optimisation Project. MACH Energy, the owner of the established open-cut Mount Pleasant Coal Mine in the Upper Hunter Valley, proposed to double output from the currently permitted 10.5 million tonnes per annum to 21 million tonnes per annum, extending operations to 2048. The existing permission runs to December 2026. If built as proposed, the expansion would make Mount Pleasant one of the largest open-cut projects in New South Wales. About 98% of its projected emissions are Scope 3 emissions.
The procedural path has been long. The Commission approved the expansion in 2022. The community group, led by president Wendy Wales, challenged that approval. After losing in the Land and Environment Court, the group succeeded 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. The proceedings were the first time the High Court was asked to consider a case on climate grounds.
The broader context here is the legal treatment of exported emissions. The majority did not prohibit coal mining or rule that Scope 3 emissions must block approval. It ruled on process, holding that a decision-maker must address mitigation and the availability of conditions to reduce downstream emissions where the statutory framework requires it. For practitioners, that shifts attention from whether offshore combustion can be counted to how consent authorities document consideration of mitigation options.
Looking at what this means for New South Wales planning, the decision narrows room for approvals that treat Scope 3 emissions as beyond conditioning. Future proponents and the Commission will need to show a record of active consideration of feasible conditions, even where enforcement across supply chains is complex and ultimate combustion occurs outside Australian jurisdiction. Opponents, in turn, have a clearer template for judicial review focused on failure to consider, rather than on the merits of climate policy. The ruling leaves open how far such conditions can practicably go, and how courts will assess adequacy when authorities do consider mitigation but decline to impose it.
