Before 1970, if a factory wanted to dump toxic waste into a river in the United States, they could get away with it. There was no Clean Water Act, no Clean Air Act, no Environmental Protection Agency. Though protests were common, they were focused on the war in Vietnam, not improving the environment. A Wisconsin senator, Gaylord Nelson, was inspired to change things; on April 22, he organized the first Earth Day, a "teach-in" on the environment. 20 million Americans demonstrated that day, and the government listened: by December, they had established the EPA and passed the Clean Water, Clean Air, and Endangered Species Acts.

The environment hasn't been "saved." It's an understatement to say that there's a long way to go, and climate change alone may be the greatest challenge that humanity has ever faced. But today, as we're thinking about the next steps toward a more sustainable future, it's worth taking a moment to think about the progress that the environmental movement has made. Since it's Earth Day-centric, the list below focuses mainly on the United States, but progress is happening all around the world.

1. Shrinking the Hole in the Ozone Layer

Products like hairspray and refrigerators used to contain CFCs, chemicals that can deplete the ozone layer (the critical part of the atmosphere that absorbs nearly all of the UV light from the sun, protecting life on earth). In 1987, 197 countries agreed to phase out CFCs. The hole in the ozone layer is still there—roughly the size of North America—but it's expected to start decreasing within a decade.

2. Cleaner Air

There's an episode of Mad Men where Don looks out the window to a sea of smog not unlike recent real-life scenes from Beijing. The radio tells him not to go outside. The Clean Air Act has helped live up to its name: cars today are 98 percent cleaner than they were in 1970, and the reduction in air pollution has prevented hundreds of thousands of premature deaths.

3. Cleaner Water

The Cuyahoga River in Ohio is famous for being so polluted in the 1960s that it often caught on fire. Today, it's illegal for factories to dump pollutants in waterways, and public drinking water is cleaner.

4. National Parks

This one long predates Earth Day, but you can also thank environmentalists for preserving 84 million acres of national parks in the United States (and another 190 million acres of national forests). After Yellowstone was established in the late 1800s, other countries were inspired to launch their own national parks. Today, one-eighth of the world's land is protected.

5. Un-endangered Species

Thanks to the Endangered Species Act, several species are no longer endangered, including grizzly bears, bald eagles, the brown pelican, and gray wolves. Out of 1800 plants and animals that have been on the endangered species list, 1791 are still around.

6. Unleaded Gasoline

More than 185 countries around the world have stopped adding lead to gasoline. Why does that matter? Lead might have been okay for cars, but for people, it's a cause of brain, kidney, and heart damage. For children, even tiny amounts of lead can lower IQ and lead to behavior problems.

7. Less Acid Rain

Until 1990, when the Clean Air Act was toughened up to include stricter emissions regulations for coal power plants, acid rain was much more common in many locations. Chemicals from the coal plants would react in the air, causing rain that killed trees and plants, and poisoned lakes. Though coal plants are still polluting—and a major source of climate change—acid rain much less of an issue.

Now for the hard news: we have, by some estimates, just a handful of years to completely turn things around if we want to avoid catastrophic climate change. Let's take inspiration from the major environmental victories of the past, and get to work. Though environmentalists of different stripes—like designers, architects, and entrepreneurs—are also making major progress, it's worth thinking about the power of policy to also make lasting change. The first Earth Day, the voice of the citizens was heard. Let's be heard again: tell your political leaders, including President Obama, if you're an American citizen, that we need action on climate change policy now.

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