A directive issued instructs Crown-owned utility Ontario Power Generation to reduce coal emission levels to two-thirds below 2003 levels by 2011.
"We have to figure out how to use our coal plants less," said OPG spokesperson Ted Gruetzner, noting other sources of power such as natural gas, hydroelectric and nuclear will have to shoulder more of the load.
The utility has until November to file a plan for achieving the goal, which requires reductions to begin next year.
New plants such as the natural gas-fired Portlands facility on Toronto's waterfront will help, said Gruetzner.
After promising to close the coal plants by 2007 and then in 2009, Premier Dalton McGuinty's government is now aiming for a 2014 closure.
The new directive makes official McGuinty's election promise last fall to reduce the pollutants spewing from coal plants by another 33 per cent, said Jack Gibbons of the Ontario Clean Air Alliance.
While he called the planned cut in emissions "a fantastic step forward," Gibbons warned Ontarians won't notice much of a difference in overall air quality.
"There's going to be less pollution but pollution is still increasing from other sources, like cars," he said. "We'll still have smog days."
Energy Minister Gerry Phillips said emissions of greenhouse gases which cause global warming from the coal plants must be 11.5 megatonnes in 2011, down from 34.5 megatonnes in 2003.
That will be the equivalent of taking up to 700,000 cars off the road, said Gibbons.
None of OPG's coal plants, such as the giant Nanticoke generating station on the north shore of Lake Erie, or the Lambton plant near Sarnia, will close as emissions are lowered, said Gruetzner.
"We don't have plans to shut coal plants or do layoffs."
The government decided to keep coal plants open until 2014 in case the province needs them to meet electricity needs."