“There’s another lesson in our history, one that offers a valuable signpost for today: The benefits of cleaner air almost always dwarf its costs. When we’re contemplating change, the price tag tends to loom larger, and those who will have to pay often exaggerate it, hoping we’ll shy away from action. But when polluters are forced to clean up, they buckle down and find the cheapest way to do it. That determination often brings innovations that make change quicker and easier than predicted. And while the cost is less than we’d feared, the benefits are often much larger, multiplying in a cascade of well-being and rising productivity. Spread among millions of people, they can be hard to see, but that doesn’t make them any less real.”