The Canadian government, using procedures recommended by the Intergovernmental Panel on Climate Change, estimates that emissions from hydroelectric operations total 0.5 megatonnes of carbon dioxide a year. But, according to the Global Forest Watch report, the real total is between 7 and 13 megatonnes of carbon dioxide per year.

Part of the reason for the difference is that government estimates assume spillways and reservoirs stop emitting carbon from submerged plants after about a decade. Hydro development releases greenhouse gases when forests and plant materials are submerged by reservoirs. As the organic material decays, the carbon and methane stored in it is released.

"The Canadian government ends up with one number and everybody assumes that must be the correct number. The newer literature indicates that net emissions extend way beyond 10 years. The government should update and clean up its reporting of emissions," said Global Forest Watch spokesperson Peter Lee.

Lee said correct and complete information is vital as Canadians make decisions about their energy future.