The suit follows up on the EPA's allegations that VW installed illegal software to cheat on emissions tests.
The deal is far from an ultimate solution to climate change, but it represents unprecedented progress.
Tension is rising between the United States and China as the deadline for a climate deal approaches.
Negotiators just took a big step forward in the fight against global warming.
After just a few days, billions of dollars have been committed to clean energy.
Sometimes taking a plane is actually more fuel-efficient than driving, research shows.
Corporate sponsors for COP21 include utility companies and a big bank with billions invested in coal mines and coal plants.
As major U.N. talks kick off in Paris, the president acknowledged America's role in causing global warming.
Presidents, diplomats, scientists, and activists are all descending on the French capital. They'll try to save the world.