U.S. President Barack Obama speaks about his vision to reduce carbon pollution while preparing the country for the impacts of climate change while at Georgetown University in Washington, June 25, 2013.

Reuters/Larry Downing

Big news from President Obama’s climate speech: He says he won’t approve construction of the Keystone XL pipeline if it will “significantly exacerbate the problem of carbon pollution.”

It’s hard to know exactly what he means by that, but it’s a surprise that he mentioned Keystone at all. Pundits expected he would keep silent on the issue.

Here’s what he said:

Grist thanks its sponsors. Become one.

I know there’s been … a lot of controversy surrounding the proposed Keystone pipeline that would carry oil from Canadian tar sands down to refineries in the Gulf. And the State Department is going through the final stages of evaluating the proposal. That’s how it’s always been done. But I do want to be clear: Allowing the Keystone pipeline to be built requires a finding that doing so would be in our nation’s interest. And our national interest will be served only if this project does not significantly exacerbate the problem of carbon pollution. The net effects of the pipeline’s impact on our climate will be absolutely critical to determining whether this project is allowed to go forward.

It seems obvious that Keystone XL would significantly increase carbon emissions by encouraging development and facilitating transport of the dirtiest fossil fuel on earth — tar-sands oil. But in its draft environmental impact statement on the pipeline, the State Department asserted otherwise.

The U.S. EPA says State is wrong and argues that Keystone would notably boost greenhouse gas emissions. Even Canadian tar-sands boosters say Keystone is necessary in order to increase their oil production: “Long-term, we do need Keystone to be able to grow the volumes in Canada,” Steve Laut, president of big oil company Canadian Natural Resources Ltd., said last month.

Climate activists put so much pressure on Obama over Keystone that he felt compelled to address it. He certainly hasn’t killed the pipeline, but it’s notable that he attached a climate litmus test to it.

Grist thanks its sponsors. Become one.