I don't believe that any government of Canada to date has yet proposed or committed to greenhouse gas targets based on science.
Speaking to the targets that the present government has laid out for Canada's emissions by 2020 and 2050, there are no public documents, to my knowledge, that the government has put out that explain where those targets came from. I'm referring to the 20% below 2006 by 2020 and the 60% to 70% below 2006 by 2050.
The government has not, to my knowledge, attempted to claim that those are science-based targets, and I'm not aware of any science on which they could be based.