A recent report from the Intergovernmental Panel on Climate Change warned the burning of fossil fuels was contributing to changing climate patterns. A team of advocates, including IPCC panel members, sent a letter to the White House urging President Obama to reject pipeline company TransCanada's application for the cross-border section of the pipeline.
"As the main pathway for tar sands to reach overseas markets, the Keystone XL pipeline would cause a sizeable expansion of tar sands production and also an increase in the related greenhouse gas pollution," their letter states.
The environmentalists said the emissions associated with the production of oil for Keystone XL are equivalent to those of seven coal fired plants on an annual basis.
Obama said he'd weigh the project against its environmental footprint. A State Department assessment of the pipeline found there would be little to no net change in the emissions if Keystone XL were built.