Premier Kathleen Wynne's cap-and-trade carbon pricing scheme hasn't even started, but it already appears her government has low-balled the cost to Ontarians.

For months, the Liberal government said cap-and-trade would increase the cost of natural gas on home heating bills by about $5 a month, after it kicks in Jan. 1. But the Ontario Energy Board now says the cost on home heating bills will be up to $6.70 more per month to start, and no lower than $5.68 more, depending on the supplier and how much gas a homeowner uses.

The government previously said the cost of cap-and-trade to the average Ontario household would be $156 a year, consisting of an $8 per month increase in the cost of gasoline (4.3 cents more per litre) and $5 more per month in home heating costs.

Recently, it said this $156 annual cost will rise to $210 by 2019, plus another $75 in that year for increased costs for other goods and services.

The problem is, the government's numbers don't add up.

Auditor General Bonnie Lysyk noted in her annual report the government expects to take in $8 billion in new revenue from cap-and-trade over the next four years, or $2 billion annually. As energy consultant Tom Adams correctly notes, virtually all that money will be paid for by Ontario consumers in the form of higher retail prices for most goods and services, since virtually all of them consume fossil fuel energy.

Assuming five million households in Ontario (there were 4.89 million in the 2011 census), that works out to $400 per year for Ontario household, starting Jan. 1.

Lysyk also reported the estimated $8 billion in added revenues the government will take in between 2017 and 2020, will achieve only minor reductions in industrial greenhouse gas emissions linked to climate change.

The government says cap-and-trade revenue will be invested in green infrastructure and to help Ontarians cope with the higher cost of living caused by carbon pricing. But based on its record to date, skepticism is warranted about anything this government says about carbon pricing.