The state government on Thursday announced it will target a whole-of-government emissions reduction of 80 per cent below 2020 levels.

It will apply to emissions from all state government agencies, including transport, health and education, and government trading enterprises.

Much of the savings will come from WA closing its state-owned coal-fired power stations by the end of the decade.

"Action on climate change is crucial to diversifying the WA economy, creating long-term jobs, managing environmental impacts, and protecting the health and wellbeing of Western Australians," Premier Mark McGowan said.

"This interim target sends a signal to the broader economy that we are serious about tackling climate change and setting up Western Australia for a healthy, prosperous, low-carbon future."

Energy efficiency measures, reduced government vehicle emissions and the use of local offsets will help the government achieve the target.

Mr McGowan last week announced state-owned generator Synergy would close the Collie coal-fired power station in October 2027 and the Muja station two years later.

About 1200 workers in the coalmining town of Collie, 200km south of Perth, are expected to be affected, although efforts will be made to diversify the town.

The Labor government has promised to invest $3.8 billion in new green power infrastructure in the state's southwest, including pumped hydro and battery storage.

However, it remains uncommitted to enshrining its new emissions reduction target in legislation.

"We're considering that. We haven't ruled that out," Mr McGowan told reporters.

"We are taking pretty significant steps down the road ... taking coal out of the grid is pretty big in terms of reducing emissions."

Environment Minister Reece Whitby said talks were under way with other sectors to produce non-government interim emissions targets.

Greenpeace's Jess Panegyres said the plan put WA "out in front of the country's energy transition", but warned the state needed to move away from major gas developments such as Woodside's proposed Scarborough project.

"It's time for Western Australia to fully embrace the renewable energy transition, and leave polluting fossil fuels in the past," she said.

"As the windiest, sunniest state in Australia, we're poised to become a renewable superpower."

Meanwhile, the McGowan government has announced it will build a third desalination plant at Alkimos, north of Perth, estimated to cost about $2 billion.

It will be entirely wind-powered and have a capacity of 100 billion litres per year, with the first stage expected to open in 2028.

The government committed $1.4 billion towards the plant in last year's budget, before settling on a location. It is yet to secure environmental approvals.

Australian Associated Press