TORONTO -- Ontario's acting environmental commissioner says the province will have problems hitting its next climate-change targets.

In a report today, Ellen Schwartzel says the government has made the right noises, but now has to deliver.

The report, which comes a day before a major climate-change conference hosted by Ontario, says the province deserves praise for its ambitious targets for cutting greenhouse-gas emissions.

However, Schwartzel says the government will miss its 2020 targets unless it takes aggressive action.

She says the transportation and building sectors are in special need of attention.

The report singles out cars and trucks as the single largest source of global-warming emissions in Ontario.

Schwartzel says the government can take credit for closing coal-fired plants but says a more ambitious suite of actions is called for.

"Climate change has already begun to cost Ontarians and the costs are only expected to grow," Schwartzel said in a statement.

On Wednesday, hundreds of delegates will attend a conference of subnational governments on climate change.