Nine days from now, on September 21, organizers of the largest climate change march in history expect at least one hundred thousand of people to join the People’s Climate March in New York City. Happening just before the United Nations holds a summit on climate change, the real goal of the march is to show convening world leaders that climate change isn’t just a policy issue that matters only to scientists and policy wonks. The idea is to show that climate action is a populist movement, too—and one that’s capable of making some noise.

While it might not get the same level of attention as the summit itself, the march is no mere sideshow. Elected officials often treat climate change as an isolated policy area—a distraction from the broader economic, humane, and stability challenges of our time. Environmentalists have tried and failed to change that perception, working within the political system and on their own. This march represents a different approach. It’s bringing in religious groups, labor unions, students, and social justice organizations—in order to show that support for fighting climate change is broad. In many ways, this effort mirrors the (so far) successful grassroots tactics of bringing attention to environmental and climate concerns like the Keystone XL pipeline and the growing fossil fuel divestment movement.

The People’s Climate March just has an even more ambitious target.

Remember, the next year is a critical one for fighting climate change. We know that at some point, very soon, humans will need to slow their use of fossil fuels if we hope to contain global warming to a manageable level. Somehow that needs to be balanced with China and India’s interests in economic and population growth. Climate experts and poorer countries hit hard by extreme weather want a binding global deal to reach emissions targets. To get there, there will be another UN meeting in Peru in December, leading up to Paris in 2015, where—activists hope—an agreement can be finalized.

Iain Keith, a campaign organizer for Avaaz, a group organizing the march, may have summed up the goals of the day best. "We realized that a march could send a powerful signal,” Keith told Inside Climate News. “Marches don't always change the world, but sometimes they are the only things that shake the system into widespread change."