Super Tuesday whittled down the Democratic race for the White House to two viable candidates — and two different visions for what to do about climate change. 

Both Joe Biden and Bernie Sanders agree Earth’s steadily rising temperatures are an “existential threat.” Both say President Trump made a grave mistake when he promised to pull the United States out of the Paris climate accord. And both offer more ambitious proposals for tackling climate change than any U.S. president ever has.

But beyond that, the former vice president and the independent senator from Vermont have diverging proposals about how exactly — and how quickly — to try to cut the country’s contributions to global warming. Here are the biggest differences on the issues, as voters head to the polls in Idaho, Michigan, Mississippi, Missouri, North Dakota and Washington next Tuesday:

1. Gas: The declining cost and growing availability of gas because of hydraulic fracturing, or fracking, has helped lead to the closure of hundreds of power plants that burn coal — the dirtiest of all fossil fuels. But gas makes its own contribution to climate change, and scientists are still trying to puzzle out just how big it is.

  • Biden wants to end new drilling on public lands and impose “aggressive” limits on the release of methane, a potent heat-trapping pollutant, from existing wells. But he stops short of calling for an immediate end to gas production and wants to spend money to research ways of capturing and using carbon dioxide from gas-fired power plants.
  • Sanders wants to undercut the entire gas industry with nationwide bans on both fracking and exporting gas to other countries. He also calls capturing carbon from the exhaust of fossil fuel plants a “false solution” to climate change.