How much extra CO2 will be emitted by the Keystone XL project?
In its comments to the State Dept., the EPA says that over a 50-year period the extra CO2 emitted from transporting tar sands oil via the Keystone XL will be 935 million metric tons.
Over this same period, global manmade emissions will be about 1.7 trillion tons — i.e., assuming constant 2011 emissions for the next 50 years, 34 billion tons (2011 est.) x 50 years.
So extra the Keystone XL emissions amount to 935 million tons/1.7 trillion tons or 0.055%.
As global emissions for the next 50 years are like to exceed 2011 levels, the actual ration of Keystone Xl emissions to total manmade emissions will be less.