Tough choices loom if the world wants to go green. The United States and other countries must decide where and how to procure the materials that make our renewable energy economy possible. To build electric vehicles, solar panels, cell phones, and millions of other devices means the world must dig more mines to extract lithium, copper, cobalt, rare earths, and nickel. But mines are deeply unpopular, even as they have a role to play in fighting climate change.