Wondering if you should buy a hybrid car or install an air-source heat pump to supplement your gas furnace and be kinder to the environment?

If you live in Alberta, Saskatchewan or Nova Scotia, probably not. These supposedly green machines rely on electricity that, in those provinces, comes mainly from coal. The heat pump may save you money, but it ultimately won't reduce your carbon footprint.

If you live in Quebec, British Columbia, Manitoba or Newfoundland and Labrador, on the other hand, your electricity comes mostly from hydro power stations. So in those parts of the country your hybrid or heat pump will be much kinder to the atmosphere than a fossil-fuelled alternative.

Elsewhere in Canada, the question gets even murkier because multiple power sources play a significant role.

In short, going green isn't always simple. Electricity is sometimes greener than fossil fuels, and sometimes not, depending on how it is generated. No source of electricity — not even wind power — has zero carbon footprint. And while greenhouse gases linked to climate change get a lot of attention, they aren't the only environmental issue to consider.

Carbon dioxide

Coal is considered the dirtiest energy source used in Canada. (Troy Fleece/Canadian Press)Coal is considered the dirtiest energy source used in Canada. Figures from the Environmental Protection Agency in the U.S., based on statistics from power plants in New York and New England, say generating a terawatt hour of electricity from coal produces 915,000 tonnes of carbon dioxide, 1,380 tonnes of nitrogen oxide and 5,691 tonnes of sulphur dioxide.

Oil (which accounts for very little Canadian power generation) is next at 748,000 tonnes of carbon dioxide, 1,283 tonnes of nitrogen oxide and 2,415 tonnes of sulphur dioxide.

Natural gas produces 535,000 tonnes of carbon dioxide, 481 tonnes of nitrogen oxide and 69 tonnes of sulphur dioxide per terawatt hour — about 58 per cent as much as coal.

Different types of coal, oil or gas and different power-plant technologies produce different emissions, notes Tim Weis, an environmental researcher at the Pembina Institute in Edmonton. Overall, he says, natural gas produces from a third to about half the emissions that coal does.

Hydroelectricity from flooded land produces about 15,000 tonnes of carbon dioxide per terawatt hour and practically no sulphur dioxide or nitrogen oxide, the EPA statistics say.

Why does hydro produce carbon dioxide, you ask? A hydro dam usually floods land that has vegetation growing on it. The submerged vegetation rots, giving off carbon dioxide and methane.

One study published in 2005 found emissions resulting from a dam in Brazil, where vegetation is lush, were 3.5 times higher than generating the same electricity from oil would have been. The situation in Canada is a bit different. Hydro-Québec says measurements from its James Bay hydro project found a significant spike in emissions in the first year an area was flooded, stabilizing to the level of a natural lake within five years.

There are also "run-of-river" hydro plants that have little or no effect on water levels, thus avoiding the rotting vegetation question.

The EPA statistics don't cover wind or tidal power, both of which produce small amounts of Canada's electricity, but neither produces significant greenhouse gases in operation.

Hidden footprints

Nuclear power plants don't emit significant greenhouse gases, but they have their own waste issues.

'We're not disposing of [nuclear waste]…It doesn't go away.'—Danny Harvey, professor

Hydro and nuclear both have larger over-all carbon footprints than you might think, says Peter Berg, associate professor of physics at the University of Ontario Institute of Technology in Oshawa, Ont., because before producing any electricity you have to build the plants.

Nuclear plants and hydro dams use tonnes of concrete. And much of North America's cement comes from plants powered by burning coal. Trucks and construction equipment also pollute.

Taking those up-front emissions into account, says Berg, a nuclear plant's lifetime greenhouse-gas emissions work out at about one-tenth of a coal plant's for the same electricity. Hydro may have higher lifetime emissions than nuclear, depending on the amount of greenhouse gas from decomposing vegetation behind a dam.

A bigger issue with nuclear, Berg adds, is the long-term storage and disposal of waste. The cost of this for Canada's nuclear plants has been estimated in the tens of billions of dollars, he says, and should ideally be taken into account in assessing the overall cost of electricity from the plants.

"We're not disposing of [nuclear waste]," says Danny Harvey, a geography professor at the University of Toronto who has written several books on energy and global warming. "It doesn't go away."

Wind farms are generally large installations that involve clearing land, pouring concrete and trucking in equipment. (Adrian Wyld/Canadian Press)

And Harvey adds that the world has about 100 years' supply of uranium left before turning to reprocessing of spent fuel, which he says would greatly increase the risk of weapons proliferation and terrorism.

Weis says the Pembina Institute is not "ideologically against nuclear, but it falls, sort of, to the bottom of the list in terms of desirability."

Wind power isn't immune to up-front costs, either. Wind farms are generally large installations that involve clearing land, pouring concrete and trucking in equipment. Berg suggests greenhouse gas emissions in the construction phase could be comparable to those from nuclear or hydro.

Solar energy contributes little to Canada's electrical supply, but is an option for homeowners. Berg says solar water heating is most practical and will pay for itself in around 12 years. Although it takes a lot of energy to manufacture solar panels, solar still has a lower carbon footprint than fossil fuels, he says.

And what about a wood stove? Burning wood produces fairly small amounts of greenhouse gases, Berg says, though it does produce particulate matter. Heating cities with wood wouldn't make sense because of the smoke and the need to transport the wood, but "if I had a cabin in the countryside or a farm that supplied enough wood … I would do it."

So if you want a simple answer to going green, you may be disappointed. Take heart, though — one thing that works everywhere is simply reducing your overall energy consumption. Insulate your attic, caulk your windows, walk or take public transit to work.

Berg says doing all those things — and avoiding air travel — may be a more effective way to reduce your carbon footprint than driving an electric car.