At $50, a carbon tax would shave about $4.8-billion from Canada's GDP in 2010, which works out to about 0.09 per cent of GDP. However by 2020, the impact would become slightly positive for the economy, working out to a 0.004 per cent increase to the GDP.
That is the result of an internal report prepared for the Conservative government, and obtained by Green Party Leader Elizabeth May through an access to information request.
The report was written by economist Mark Jaccard and analyzes the potential impacts of various climate change measures on Canada's GDP including carbon taxes ranging from $10 to $250. If you're not familiar with Mark Jaccard, you should be. He is one of the world's foremost experts specializing in energy related issues and policy. Jaccard's also been a vocal advocate for the development of a sustainable energy future for the province of BC, but although he consistently has the ear of environmental advocates, he is not an "environmentalist".
His views are those of an informed realist that recognizes the need to meet the energy needs of the developing world as well as the critical goal of reducing greenhouse gas emissions. He's not against the use of fossil fuels, but he is adamantly in favour of creating policy and economic systems that encourage the solutions we need to drastically curb emissions.