The Albanese government’s decision to approve one of the world’s largest gas projects in Western Australia is being challenged in the federal court, setting up a significant test of how Australia’s environment law deals with the climate crisis.

The Australian Conservation Foundation (ACF) and Friends of Australian Rock Art (Fara) are this week running concurrent court challenges against the approval of the extension of Woodside’s major North West Shelf gas export project.

The environment minister Murray Watt’s approval of the project last year was met with fury from conservationists and the Greens.

The approval, allowing Woodside’s Karratha gas processing plant to operate until 2070, has been described as a “carbon bomb” and according to ACF would see about 4bn tonnes of CO2 released into the atmosphere – equivalent to about 10 years of Australia’s annual emissions.

The gas plant operates beside the Murujuga indigenous rock art complex – a landscape of more than a million petroglyphs dating back 50,000 years, including the oldest known image of a human face.

In a significant step, a UN special rapporteur has been allowed to intervene in the case to advise the court of Australia’s international climate obligations.

Representatives from Fara and ACF and their supporters gathered outside court in Melbourne on Tuesday before the case before Justice Catherine Button.

Adam Bandt, chief executive of the Australian Conservation Foundation (ACF), said: “It will be up to the court to decide the merits of the case … We’re here saying the minister made the wrong decision and that some very significant factors including around climate change need to be taken into account.”

The ACF will argue the minster failed to properly consider how emissions from the gas plant could be a “substantial cause” of damage to Australia’s protected environment.

The conservation group will argue the minister didn’t have enough detail about the gas the plan was going to process – partly because it would involve processing third-party gas from as yet unapproved projects – to make a decision.

The ACF will also argue the minister incorrectly considered the claimed economic benefits of the gas plant, a point also being argued by Fara.

Critics, including Fara, have argued industrial emissions from the plant are already causing erosion of the petroglyphs and this would be worsened by the decision to extend the project.

While government-backed monitoring of the rock art has mostly dismissed those concerns, some scientists remain unconvinced.

As part of the case, Fara is also seeking details of meetings between Watt and Woodside while the minister and his office were negotiating conditions of the approval.

Fara will argue the minister did not properly identify the risks to the rock art from the project.

Fara, a volunteer group formed 20 years ago, helped secure national heritage listing of the area in 2007, creating the legal trigger for assessment of the project under federal environment laws.

The United Nations special rapporteur on the human right to a clean, healthy and sustainable environment, Astrid Puentes Riaño, has been given leave to be a “friend of the court” in the hearings, laying out in written submissions to the court Australia’s environmental obligations under international law.

The intervention was made in the legal context of the International Court of Justice’s landmark ruling last year that countries must prevent harm to the climate system and failure to do so could result in them being ordered to pay reparations.

“Under customary international law, Australia is subject to a duty to prevent significant harm to the environment,” Puentes’ submission reads. “The ICJ Advisory Opinion confirmed that this duty applies to the environment and the climate system.”

A spokesperson for Woodside said: “The Australian Federal Government’s September 2025 approval of the North West Shelf Project Extension followed a comprehensive and extended assessment carried out by both Commonwealth and Western Australian State regulators in accordance with statutory processes.

“As proceedings are before the court, we have no further comment.”

Guardian Australia has requested comment from Watt.

The case is expected to run all week with a further day set aside next Monday.