If you're out and about in New York City this week, you may have noticed a few more people than usual handing out fliers in the subway.

These dedicated recruiters are volunteers for the People's Climate March — a New York City-based event touted as the "largest climate march in history" — and they're on their A-game this week: The march is only five days away, and they're expecting hundreds of thousands to attend.

The ads are running everywhere, from the New York Times Website to subway walls. Ads for the People's Climate March are everywhere. Lauren Friedman/Business Insider The march was born shortly after it was announced that this year's UN Climate Summit— a gathering of international leaders to discuss actions and solutions to the problem of global climate change — would occur in New York City, said spokesperson Maryam Adrangi. The movement was spearheaded by local organizations hoping to express their concern over climate change during the week leading up to the summit.

But with climate change threatening just about every aspect of life on earth, from our shrinking shorelines to our vanishing biodiversity, it's a problem far bigger than the confines of New York City — and participation in the People's Climate March has grown to reflect this fact. In the months since its inception, it's become an international project.

The main event will occur this Sunday, Sept. 21, starting at 11:30 a.m., and will carry participants more than 50 blocks, from 86th St. down to 34th St. Here's where they will be walking, starting in six themed groups: And making their way downtown: Around the country and the world, similar events have sprung up in a show of solidarity: In fact, demonstrations will be held on every inhabited continent, as the map below shows.

"People's Climate Marches" around the world. People's Climate March/Google Maps Events will continue to ramp up in New York this week and will continue on in the days following the march, with workshops, exhibits, and demonstrations being hosted by various organizations around the city.

There's also a train currently en route from California, bearing participants interested in mingling and networking with other activists before they reach the East Coast. Passengers will have the opportunity to engage in talks and workshops on the journey to New York, like this one tweeted by the Center for Biological Diversity:

The event is picking up speed on social media, with hashtags on Twitter, Tumblr, and Instagram (including #pcm, #peoplesclimate, and #peoplesclimatemarch). Here's what people are saying:

"We're tired of winning the argument and losing the fight. And so we march." http://t.co/oAMChqFNLp #peoplesclimatemarch— The Nation (@thenation) September 16, 2014

To change everything, we need everyone on board. Join the largest climate march in history on 9/21. #peoplesclimate #peoplesclimatemarch— Projects For All (@ProjectsForAll) September 10, 2014

With more than 1,000 participating organizations and what's looking more and more like hundreds of thousands of individuals, it's a big response to a big problem — and may be one for the history books.

There'll be a Bee-In at Bowling Green Park, where the public can interact with beekeepers and learn how climate change is destroying this keystone species. On Monday another group is planning a Financial District Sit-In of climate activists in Battery Park, starting at noon.