Air

Greenhouse gases

Greenhouse gases such as carbon dioxide, methane and water vapor contribute to the greenhouse effect, a natural phenomenon that traps heat in the atmosphere. The gases result from natural processes (such as volcanoes, cloud cover and ocean currents) and human activities (such as the burning of fossil fuels and, at a lower level, the creation of reservoirs).

Hydro plants have mixed impacts on greenhouse gas emissions. Hydroelectricity helps to lower Canada’s overall greenhouse gas emissions by replacing some of the need for fossil fuel-fired power. However, reservoirs, like natural lakes and streams, emit carbon dioxide and methane. When a reservoir is filled and vegetation is submerged, methane and carbon dioxide can be produced as the vegetation decomposes.

The Canadian Hydropower Association estimates that hydropower in Canada generates about 15,000 tonnes or less of carbon-dioxide equivalent for each gigawatt-hour of electricity produced.

Although greenhouse gas emissions from reservoirs are small compared with emissions from other energy sources, the industry is conducting studies to better understand the source of emissions and to identify solutions. One option being used is clearing vegetation before an area is flooded.