Every day we're bombarded with news about global warming, pollution, and the environment's perilous position. But as bad as things are right now, it's important to remember that they used to be even worse. Progress is possible and we've already made plenty of it.

In an effort to fight rampant pollution and horrendous air quality around American cities in the '50s and '60s, President Richard Nixon signed the Clean Air Act of 1970. The act tasked the EPA with setting national air quality standards and working with states to enforce them. Young people have no idea how bad it used to be. 

Here are 20 photos of what breathing looked like in the 1970s and a few modern skylines to show you how far we've come.