The case was brought by seven young people who argue Ontario's weakened emissions target violated the Charter.

They allege the target violated their right to life in part by committing Ontario to dangerously high levels of planet-warming emissions and discriminated against them as youth who will bear the brunt of the impacts.

Fraser Thomson, a lawyer representing the young people, says Ontario's application "opens the door to a generation-defining hearing before Canada's highest court."

The case dates back to when Premier Doug Ford's then-newly elected Progressive Conservative government repealed the law underpinning Ontario's cap-and-trade system for lowering emissions.

The government scrapped the system in 2018 and replaced the emissions target in that law — 37 per cent below 1990 levels by 2030 — with a new target of 30 per cent below 2005 levels.

The young people suggest the revised target allows for additional annual emissions equivalent to about seven million passenger vehicles.