In a world without people, how fast would NYC fall apart? Here's the timeline.

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17 hours ago

Imagine the ceaseless cacophony of New York City suddenly stopped. No sirens wailed. No cars zoomed. No subways rumbled beneath sidewalks. All eight million New Yorkers disappeared overnight.
Now, imagine what would happen next. If no one's around to sweep the sidewalks, weed Central Park, or turn the power grid on, nature would move in—and quick. Dandelions would spring up in asphalt cracks. Raccoons would move into abandoned apartments. Sidewalk trees would outgrow their planters.
But just how swiftly would the city disappear beneath a curtain of green? We talked to architects and urban ecologists to map out a potential timeline.
With no one to maintain the power grid, the Big Apple would go dark within a few days. The Milky Way would illuminate Midtown as light pollution disappears overnight. Without air conditioning and heat, 'you start getting weird temperatures inside the building. Mold starts to form on the walls,' says architect Jana Horvat of the University of Zagreb, who studies building decay.
Some green energy projects in the city might stay lit for longer, such as the solar and wind-powered Ricoh Americas billboard in Times Square. Eventually, though, even the Ricoh billboard would go dark; not because the billboard would lose power, but because there would be no one to replace its LED lightbulbs.
Without power, the pump rooms that clear out 13 million gallons of water daily from the subway would be useless, and the train tunnels would begin to flood. 'Probably this water would result in [the subway] being, you know, occupied by new species,' says Horvat. 'Some plants would start growing, some animals' would move in. Likely, species that already thrive in the subway—rats, cockroaches, pigeons, opossums—would be the first ones to take advantage of the human-free passages.
Within the first month, the manicured lawns of Central and Prospect Park would grow wild and unkept. 'When you stop mowing a lawn, you get a meadow,' says botanist Peter Del Tredici, a senior research scientist emeritus at the Arnold Arboretum of Harvard University, who wrote a book on urban plant life. Within a month, dandelions, ragweed, and yellow nutsedge would start popping up in the now knee-high grasses of New York's iconic parks. 'First, it's herbaceous plants, but then, you know, you get trees and shrubs and vines,' says Tredici.
In a year without people, many of New York's buildings would start to deteriorate. 'The glass facades would be the first to go,' says Horvat. The single-pane glass on brownstones and family homes would be the most vulnerable, but in a decade, even the heat-strengthened glass on skyscrapers would start to wear down and crack. And once windows break, water gets in. 'Then you'll have plants start growing in there,' says Tredici. Apartments would transform into humid hothouses, the perfect habitat for mosquitoes, water snakes, fungus, and rushes. 'It's like a wetland on the second floor.'
Without maintenance, the asphalt streets and parking lots in New York would quickly degrade. Freeze-thaw cycles would create cracks. 'Water settles in that crack, and then that's all the plants need,' says Tredici. First, mosses would grow. Within a decade, young trees may even sprout. The London planetree, the most common street tree in New York, is particularly known for its resilience and fast growth rate, and any of its offspring could quickly find a toehold in a deteriorating asphalt parking lot.
Within a decade, the Statue of Liberty would also start to deteriorate. The statue's copper plating would start to split, allowing sea spray to break down its interior steel skeleton. Steel 'is a very durable material, but it is very prone to corroding if it comes in contact with damp conditions,' says Horvat: That's bad news for New York, a city made from steel.
In the decades since humans abandoned New York, a 'novel ecosystem' would emerge, says Tredici. 'It's not going to look like anything that's ever existed anywhere in the world.'
Tredici points to Detroit as a case study. Today, crabapple trees—tough ornamentals native to the Central Asian mountains—blanket Detroit. 'They actually will spread all over,' says Tredici, and after 50 years without humans, Central and Riverside Park's crabapple trees would grow among a young forest full of London planetrees, honeylocusts, pin oaks, and Norway maples (the last three being common New York street trees). Nightshade vines and poison ivy would creep up buildings, and mosses and resilient weeds would cover the higher reaches of exposed windy skyscrapers.
Among the greenery, more and more animals would call Manhattan home. Deer, rabbits, groundhogs, and wild turkeys would move in. Larger predators—coyotes, bobcats, black bears, and copperhead snakes—would follow. Peregrine falcons, bald eagles, red-tailed hawks, and great horned owls would nest in hollowed-out buildings, while feral cats prowl the abandoned upper floors of apartment buildings, feasting on mice and birds.
Despite their futuristic look, the city's newest spires, such as 10 Hudson Yards and 111 West 57th Street, would be the first to fall. These buildings rely on slender, reinforced steel skeletons encased in reinforced concrete. But when the power shuts off and water seeps in through these buildings' glass curtain walls, these high-rises would rot from the inside out.
The Empire State Building and Chrysler Building would likely outlast their younger rivals. Built to support much more weight than necessary (a safety precaution in the early days of skyscrapers), these giants' steel frames are bolstered by thick masonry and interior walls. Ten Hudson Yards might last a century. The Empire State Building might last 50 years longer, but eventually even these historic titans would collapse.
After a century, New York City would 'become a forest,' says Tredici. A canopy of mature trees over a 100-feet-tall would replace the city's skyscrapers. Soil would regenerate. Concrete, one of the world's 'strongest' construction materials, says Horvat, would dissolve. New York's carefully manicured river parks, such as the Hudson River and East River Park, would transform into wetlands teeming with eels, egrets, turtles, beavers, and muskrats.
But even as skyscrapers fell and forests grew, parts of New York would 'survive for centuries in this ruinous state,' says Horvat. Cracked marble lions would stalk the forest floor. Soil and underbrush would obscure once-gleaming granite fountains. Rusted steel beams would jut out from dense root systems. Even without humans, pieces of New York would endure—a fragile legacy for the future to either uncover or forget.
This story is part of Popular Science's Ask Us Anything series, where we answer your most outlandish, mind-burning questions, from the ordinary to the off-the-wall. Have something you've always wanted to know? Ask us.