A study for The Canadian Nuclear Association is questioning just how green wind power is.

The association points to an independent study of life-cycle carbon emissions from Toronto-based engineering firm Hatch Ltd.

The study compares greenhouse gas emissions from nuclear power plants, to emissions from wind farms backed by natural gas plants.

The association says wind plants only operate when wind blows, so they need back up, often from natural gas plants.

The analysis estimated nuclear power emitted 18.5 grams of greenhouse gases per kilowatt-hour (kWh) through the entire life cycle, compared to 385 grams per kWh for wind backed by natural gas.

However, the Hatch study does not mention that the Bruce Power nuclear plant is unique in that it can power down when the wind is blowing.

The study does not take nuclear waste into account.