The U.S. State Department’s final environmental review of the Keystone XL Pipeline may have underestimated carbon dioxide emissions associated with the pipeline by as much as four times, according to a new study published in Nature Climate Change. The addition of Keystone XL crude oil to the market will drive global oil prices down, the authors say, which in turn will increase demand for oil worldwide — by as much as 0.6 barrels for every barrel of Keystone XL oil added to the market. The extra oil consumption could add up to 110 million tons of CO2 to the atmosphere each year, an amount four times larger than the State Department’s estimate of up to 27 million tons annually, according to the study. President Obama has said he will let the pipeline proceed only if it will not "significantly exacerbate" greenhouse gas emissions. The State Department’s final review determined that the pipeline’s effect on climate change would be negligible, but that analysis did not take into account the increase in crude oil demand that could be sparked by Keystone XL, the authors of the new study say.