Glenn Murray says carbon taxes will take too long to work, given how quickly the planet is warming.
But Legault says the cap and trade system is still viable without the US state.
Ontario, Alberta, Manitoba, New Brunswick and BC have also filed notices of intervention in the province’s appeal.
He has undone many of the Liberals’ signature policies.
Government plan proposes to spur private investment in clean technologies, create performance standards for large emitters.
Doug Ford’s government has already cancelled most programs financed through cap and trade revenues.
Financial watchdog says loss is greater than the savings achieved by cutting program spending.
Doug Ford is also to speak Friday at a “Scrap The Carbon Tax Rally” in Calgary.
Greenpeace says the government flouted the province’s Environmental Bill of Rights by failing to hold public consultations.
Ford says the change will save families $80 a year and small businesses will save $285 annually.
Proposed legislation will set out the legal framework to wind down the program.
The speech, which opens a summer sitting of provincial parliament, is expected to focus on the Tory’s immediate priorities.
The fund is tied to Ontario’s cap-and-trade system, which Doug Ford has begun dismantling.
$420 million earmarked for Ontario under the Low Carbon Economy Leadership Fund is under review.
Money will flow instead to Alberta and US markets, says Toronto-based SolarWall.