Yet even as the price of inaction grows more tangible, a second structural barrier impedes legislative action. Much like gun control, climate is an issue that unites Republicans by ideology but divides Democrats by geography. Even if Democrats can build a bigger Senate majority through the next few election cycles—they are positioned to add seats in 2016 even if they lose control in 2014—such gains probably won’t produce the 60 votes needed to break a filibuster against legislation to limit carbon emissions.

The Democrats’ problem is that they cannot build a big Senate majority without winning seats in states heavily dependent on coal, which would suffer the most from limits on carbon. Democrats now hold 21 of the Senate seats in the 19 states that rely on coal to produce a majority of their electricity and half of the seats in the 10 states (some overlapping) that mine the most coal. Resistance from some coal-state Democrats doomed climate legislation in 2009, even when the party controlled 60 Senate seats and then-Speaker Nancy Pelosi narrowly muscled a cap-and-trade bill through the House. Senate Democrats such as North Dakota’s Heidi Heitkamp and Indiana’s Joe Donnelly remain equally unenthusiastic today.

Theoretically, those Democratic votes could be replaced by Republican votes from states less reliant on coal. But Republicans face overwhelming ideological pressure to oppose action on climate change and even to reject the scientific consensus that it is occurring, as Sen. Marco Rubio from vulnerable Florida demonstrated in his dismissal of the federal climate report. Republican unity and Democratic division promises a permanent legislative stalemate over climate.