In her progress report, Ellen Schwartzel said car and truck emissions and energy-hogging buildings present the single biggest problem and opportunity in the province's fight against climate change.
"In a world of rapidly melting Arctic sea ice, there is a real urgency to reducing emissions now," Schwartzel said.
"Delay reduces the choices we can make to prevent worse climate consequences down the road."
The report, which comes as Ontario is set to host hundreds of delegates at a climate-change summit for subnational governments that starts Wednesday in Toronto, praises the Liberal government for having the right ideas.
The government can take credit for having closed its coal-fired plants and incorporating climate change into its planning, but ambitious actions are now called for now, Schwartzel said.
The province's own targets call for its greenhouse-gas emissions to fall to 15 per cent below the levels they were in 1990 by 2020. To make that happen, the report called "Feeling the Heat" urges among other things aggressive measures to tackle vehicle emissions.
A key way to do that would be to boost the use of electric vehicles by promoting incentives and ensuring "super cheap" electricity at night to make charging them more convenient and affordable, the report says.
"Our power supply, our electricity, is very low carbon, so it makes a lot of sense to use that to electrify transportation more and more," Schwartzel said.
The report also calls for more urgency in ratcheting up energy-efficiency standards for new buildings and providing incentives for retrofitting existing ones to make them greener.
The province, Schwartzel said, has created the right pre-conditions to meet its targets, but now is the time for action.
"It can be achieved. We just really need to buckle down and do it."
In response to the report, Environment Minister Glen Murray said he agreed with the commissioner that the need to cut greenhouse gases is urgent.
As examples of provincial action, Murray cited the province's plans for multibillion-dollar investments in public transit and a cap-and-trade system to limit emissions. What's really needed, he said, is for the federal government under Conservative Prime Minister Stephen Harper to take climate change seriously.
However, Peter Tabuns, with the provincial New Democrats, said government efforts have lagged.
"The government has put the climate-change file on the back burner for a number of years — it relied on the recession," Tabuns said.
The province, he said, should be doing more to curb urban sprawl, provide incentives to retrofit homes and office buildings, and electrify trains in the greater Toronto area.
The Greens' Mike Schreiner called for high-speed charging stations to be erected along major highways as one way to motivate motorists to go electric.