Numbering in the hundreds of thousands, they stepped, strutted, soldiered and sauntered through the streets of New York, their footfalls kicking up a thundering message of concern for their children, their grandchildren and their own futures unless world leaders act.

“We’re sending a clear message that enough is enough,” said Crystal Lameman of Beaver Lake Cree Nation in North Alberta, Canada, as she marched down Sixth Avenue, just south of Central Park. “These are real human lives.”

Among her biggest concerns: the rights of the world’s indigenous people to live free of the pollution caused by fracking.

Lameman’s sense of urgency was shared by Kathy Selleck, a 57-year-old nurse from Boston. “To get our voices heard,” she said in response to a question about what she was hoping to accomplish. “Because we’re tired of all the white noise getting in the way. The time has come.”

Selleck was bedecked in a pair of homemade wings intended to look like those of a monarch butterfly, whose numbers are in decline. “Today, I’m thinking of monarchs,” she said.

As they marched, drumbeats and chanting pulsed through the crowd. “Hey, hey! Ho, ho! Climate change has got to go!”

Some let their T-shirts or signs speak for them. “Yalies choose climate justice,” read one.

“Live green, love green, be green,” read another.

“Stop the rape of the world!” read a third.

And one appeared to take inspiration from Bob Dylan: “The tides, they are a changing,” it read.

Many of the marchers were aware that human monarchs and other world leaders plan to descend Tuesday on United Nations Headquarters in New York for Secretary-General Ban Ki-moon’s Climate Summit.

Ban himself linked arms with the marchers. “There is no Plan B because we do not have Planet B,” he told reporters.

Trudy Vermehren said change could take decades. “I think, in about 20 years, we might start making changes,” said the 56-year-old landscaper from Cape Cod, Massachusetts. “I wish it would be this week at the UN Summit.”

Though some of the marchers were wearing T-shirts and other memorabilia picked up during other fights – espousing everything from women’s rights to children’s rights to union rights – the day was a rarity for Phil Kramer, a 58-year-old advertising executive from Boston. “The last time I was in one of these was Earth Day,” he said, referring to the 1970 event that is credited for kicking off awareness about the environment.

Marilyn Schramm was walking slowly, with a cane. The 62-year-old retired lawyer said she needs a new hip, but decided to march anyway. “We have to show that it’s a worldwide concern of the people,” she said. “We have to show that we are not going to sit back.”

Though she has no children, she was happy to see youths among the marchers. “They’re the ones who are going to have to bring about the change,” she said.

And she was also glad to see indigenous people marching with her. “What bothers me is the people who caused the problem themost aren’t suffering the most.”

But she expressed doubt that her effort would yield any tangible benefit soon. “I will probably be dead and gone before the worst of it hits,” she said.

Jeff Ostman made the trek in from northwest New Jersey with his wife, Cathy. The 58-year-old reclaims refrigerant for a living, but was not marching. Weakened by multiple sclerosis, the heating and air conditioning specialist was watching the event from an area set up along Sixth Avenue for wheelchairs.

His message to the heads of state who will be in the UN on Tuesday? “It’s not just a meeting,” he said. “You’ve got to accomplish something.”

Angela Fonda, an attorney in Atlanta city government, was celebrating her 50th birthday with her husband by participating. “We are speaking to global leadership,” she said. ”We can all do well and thrive if we just clean up our act.”

“I hope that the world leaders will come to a conclusion to make this world greener and a better place to live,” said Paldon Dolma, a 19-year-old freshman at Hunter College. The political science major left Tibet in 2002, then moved to India until 2007, when she moved again – this time to the United States.

She said she hoped to highlight the environmental exploitation of Tibet by China. Sunday’s march was her first. “This is a very big thing,” she said.

Nawan Gurung was also among the throng. He said he was 6 years old when he began working as a shepherd in the mountains of Nepal, tending to flocks of 200 to 300 goats and sheep.

“You could see snow-covered mountains and glaciers,” he said. Gurung, now 28 and studying cultural anthropology at Columbia University, recently returned to Nepal and was dismayed at what he found. “All the streams have dried out,” he said. And the ice packs that once covered the mountain tops have retreated.

The issues on Sunday were nothing new to Fred Cunningham. The 72-year-old engineer from Stamford, Connecticut, said he studied renewable energy more than 50 years ago at MIT but had never carried a sign or otherwise participated in a demonstration.

That all changed on Sunday, when he was carrying a sign that read, “End Iithiocracy.”

“It means end government by idiots,” Cunningham translated from the Greek.

Why did he feel compelled to take up activism now? He hesitated, his voice caught, and he finally blurted out huskily, “My grandchildren.”

And what message would he give to the world leaders on Tuesday? He turned for inspiration to a Chinese philosopher. “A nation, to be a leader, has to set a good example.”

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus

Photo: Caitlin McManus