A new study from the Stockholm Environment Institute says that the Keystone XL pipeline could emit four times more greenhouse gas than originally estimated.

Earlier this year, the US State Department estimated that the pipeline could increase emissions of greenhouse gases annually by around 1.3 million to 27.4 million metric tons. The new study, however, shows that it would likely increase emissions by as much as 121 million metric tons.

Authors of the study Peter Erickson and Michael Lazarus wrote, “The sole reason for this difference is that we account for the changes in global oil consumption resulting from increasing oil sands production levels, whereas the State Department does not.”

The study also predicts that oil prices could go down to $3 a barrel, therefore increasing consumption, which would also have a negative effect on the environment.

“Our simple model shows that, to the extent that Keystone XL leads to greater oil sands production, the pipeline’s effect on oil prices could substantially increase its total GHG (greenhouse gas) impact,” Erickson and Lazarus wrote.

The proposed pipeline would stretch from Hardisty, Alberta, Canada to Steele City, Nebraska, and connect to an existing pipeline which goes to the Gulf Coast of Texas. Energy companies have not been able to build the structure already because it requires federal approval as it would cross the Canadian border.

President Obama has repeatedly said that he would allow the $5 billion pipeline’s construction “only if this project does not significantly exacerbate the problem of carbon pollution.”

It’s a tricky decision for the president to make. The pipeline’s supporters are calling for its approval on the grounds that it will lessen America’s dependence on foreign oil and that it will create jobs. Other than the obvious toll the additional greenhouse gases will take on the environment, those opposed to the project point out that, once it is complete, the pipeline will only create 35 permanent jobs — hardly a major boost to the US workforce.

In April, eleven Democratic senators called on the president to make a final decision on the pipeline’s approval no later than May 31.

They’re still waiting for an answer.