Ontario's cap-and-trade auctions brought in nearly $2 billion in its first year, ahead of entering a joint market with Quebec and California next year.

The final auction took place last week and results released Wednesday show that 83 per cent of current credits were sold, giving the province $422 million.

That means that the province's system aimed at lowering greenhouse gas emissions has brought in $1.9 billion for green projects in 2017, such as energy efficient improvements at hospitals, green rebates for homeowners, and bike lanes.

Environment Minister Chris Ballard said in a statement that Wednesday's results show the system is functioning as it should.

It puts caps on the amount of pollution companies in certain industries can emit, and if they exceed those limits they must buy allowances at auction or from other companies that come in under their limits.

Ontario's three previous auctions sold out of current credits. The government has previously said it didn't expect every single auction to sell out, as the market fluctuates.

Keith Brooks of Environmental Defence said the latest results are a strong showing, considering the uncertainty around the future of cap and trade in Ontario.

"I think it shows that cap and trade is off to a really good start," he said. "I think it shows that businesses have understood how the markets are going to work."

The Liberal government has signed an agreement to link with Quebec and California's carbon market on Jan. 1, but the Progressive Conservatives, who are ahead in the polls, have promised to dismantle the program and instead implement a carbon tax if they win next year's election.

Critics in Ontario have slammed both cap-and-trade's cost to consumers -- an extra 4.3 cents per litre to the price of gasoline and about $80 a year to natural gas home heating costs, as well as indirect costs -- and the potential cost to the economy.

The auditor general has said that when Ontario links its market with Quebec and California, an estimated $466 million will leave the Ontario economy over three years, because it will be cheaper to buy allowances from those jurisdictions.

But the Liberal government has staunchly defended the plan, saying it is far more cost effective and is more effective at reducing emissions than a carbon tax. The Tories decry the Liberals' cap-and-trade program as a "cash grab."