Two years? It's already too late.
Given the access the pipeline will grant tar sands oil to overseas markets and the advantage that pipelines have over rail, the Keystone XL will undoubtedly support tar sands production, promote continued tar sands investment, and contribute to Canada’s already significant greenhouse gas output.
So, if the decision really comes down to the pipeline's climate impact - and not something else - the choice is clear.
Two years? It's already too late.
Not peer reviewed? :P