Today, President Obama made a bold proclamation that he will not approve Keystone XL if it contributes to climate pollution. He said that, “Our national interest will be served only if this pipeline does not significantly exacerbate the climate problem.” It is now up to the State Department to prove that the pipeline will not increase greenhouse gas (GHG) emissions.
With this promise to the American people to reject the pipeline if it will increase climate pollution, the President has taken a huge step towards rejecting Keystone XL, given that evidence has already shown that the pipeline will increase GHG emissions and have serious climate consequences.

The EPA said that State Department assessment of Keystone XL climate impacts must be more “complete and accurate.”
“The market analysis and the conclusion that oil sands crude will find a way to market with or without the Project is the central finding that supports the DSEIS’s conclusions regarding the Project’s potential GHG emissions impacts. Because the market analysis is so central to this key conclusion, we think it is important that it be as complete and accurate as possible. We note that the discussion in the DSEIS regarding energy markets, while informative, is not based on an updated energy-economic modeling effort.” [EPA, 4/22/13]

Congressional Research Service stated the Keystone XL would increase U.S. greenhouse gas emissions by 3 million to 21 million metric tons.
Based on a survey of published literature, the nonpartisan Congressional Research Service noted: “[T]he estimated effect of the proposed Keystone XL pipeline on the U.S. GHG footprint would be an increase of 3 million to 21 million metric tons of GHG emissions annually (equal to the annual GHG emissions from the combustion of fuels in approximately 588,000 to 4,061,000 passenger vehicles); and the estimated effect of the Keystone XL pipeline on global GHG emissions remains uncertain, as some speculate that its construction would encourage an expansion of oil sands development, while others suggest that the project would not substantially influence either the rate or magnitude of oil extraction activities in Canada or the overall volume of crude oil transported to and refined in the United States.” [Congressional Research Service, 3/15/13]

Eighteen of the nation’s top climate scientists released a letter to President Obama today urging him to reject the Keystone XL tar sands pipeline. 
“We hope, as scientists, that you will demonstrate the seriousness of your climate convictions by refusing to permit Keystone XL; to do otherwise would be to undermine your legacy.”

Industry insiders agree that without Keystone XL, tar sands expansion cannot proceed as planned. Less tar sands development means less GHG emissions.

• “Even if all the pipelines being planned were built, there would not be enough capacity to handle the growth that companies have laid out in their expansion plans.” Globe and Mail
• “Canada’s oil industry is facing a serious challenge to its long-term growth. Current oil production in Western Canada coupled with significant gains in U.S. domestic production have led the industry to bump up against capacity constraints in existing pipelines and refineries.” Financial Post
• “This is why Keystone is so important for us – because we have this refinery capable of treating our crude and today we are missing that opportunity because of that logistical constraint.” Andre Goffart, Total E&P Canada Ltd. President

Even the State Department, in its extremely conservative analysis in the Supplemental Environmental Impact Statement, acknowledged that the project will increase GHGs. 
“The annual CO2e emissions from the proposed Project is equivalent to CO2e emissions from approximately 626,000 passenger vehicles operating for one year.” [State Department, 3/2013]

All evidence shows that Keystone XL will have serious climate impacts. 
The NRDC climate backgrounder gives a good overview on greenhouse gas emissions and Keystone XL.