Kelly Nichols and her best friend, Michelle Ramoni, march in New York. (Photo by Yana Paskova/For The Washington Post)

NEW YORK — She liked to keep her political views secret from the world, safe from judgment.

That was before Superstorm Sandy destroyed her apartment.

This weekend, Kelly Nichols returned to New York City, her former home of 13 years, to protest a future she deems dangerous for her nearly 3-year-old twins, Owen and Vivian.

She fled the East Coast to protect them.

On Sunday, 37-year-old Nichols joined more than 100,000 demonstrators — including Al Gore, Mark Ruffalo and Leonardo DiCaprio — for the People’s Climate March, billed as the largest of its kind in history.

Two days before the United Nations Climate Summit, where President Obama and other world leaders will debate environmental action, crowds started in Central Park and rolled through Manhattan, chanting: “What do we want? Climate justice!”

Barbara Abbott-McGhee, from the Manhattan Country School, and her nine-year-old daughter, Alicia McGhee, march through Columbus Circle during the People’s Climate March in Manhattan, NY, on September 21, 2014. (Photo by Yana Paskova/For The Washington Post)

They came from across the country, generations and cultures. They called for stricter carbon regulations and help for endangered species, among other green demands. They dressed as polar bears, corn cobs, gold-dusted Sun Gods.

Nichols, brown hair pulled into a low-maintenance ponytail, simply wore a pin — MOM-PARTISAN — and waved a message: I’m marching for my babies.

She strolled with the Moms Clean Air Force, a national advocacy group, cracking jokes: “Where’s the Port-O-Potty? I should have brought adult diapers…” She plans to start a local chapter in Chicago, where her family moved last year to escape climate change.

“I had to leave,” Nichols told a clean air attorney Sunday, also marching. “I do miss the city. But if something like Sandy happens again, how am I supposed to get my kids out of here safely?”

They were in Australia, visiting her husband’s family, when the superstorm struck in 2012. It took two weeks and three layovers — Germany, Singapore, Detroit – to get back to New York.

They stayed with a friend in Albany, sniffling from travel-induced colds, until it was safe to return home.

Their Hoboken, New Jersey apartment stank of spoiled food; the electricity was cut off in the storm. Two gallons of breast milk (and about a month of mother labor) was gone. The basement, flooded.

Activists carried props in the People’s Climate March. (Photo by Yana Paskova/For The Washington Post)

Nichols thought of this as she marched through New York City, her first visit since the move. It was transformative, her environmentalist origin story.

Growing up, she was the toddler who performed ABBA songs on her parents’ fireplace. She dreamed of playing Maria in the Sound of Music.

After graduating from the University of Minnesota-Duluth, she built a stage career in New York City, her dreamland, singing and sword-fighting in community shows.

She met her husband, an Australian businessman, at a karaoke bar in the East Village. They intended to stay there forever — but Hurricane Sandy shifted Nichols’ attention from acting to activism.

Her new passion is full-time.

She studies weather patterns with growing anxiety and references some scientists’ claims that severe weather events will strike more often, thanks to global warming. The same researchers say it’s impossible to directly tie storms like Sandy to climate change — but they generally agree climate change makes catastrophic weather more likely to occur. (Coincidentally, Nichol’s Chicago street flooded during her housewarming party.)

She Googled ways to get the word out and found the Moms Clean Air Force. She traveled with the group to Washington, D.C. earlier this summer for her first-ever political demonstration. The People’s Climate March was her second.

Her twins, with her husband’s help, Skyped her Sunday by cell-phone. She pointed her screen toward the protesters.

“Hi, babies!” she yelled. “I love you! I’m doing this for you!”