In a coastal town in Washington, climate change has a high school junior worried about the floods that keep deluging his school. A 17-year-old from Texas says global warming scares him so much he can’t even think about it.

But across the country, teens are channeling their anxieties into activism. “Fear,” says Maryland 16-year-old Madeline Graham, an organizer of a student protest planned for this week, “is a commodity we don’t have time for if we’re going to win the fight.”

A solid majority of American teenagers are convinced that humans are changing the Earth’s climate and believe that it will harm them personally and other members of their generation, according to a new Washington Post-Kaiser Family Foundation poll. Roughly 1 in 4 have participated in a walkout, attended a rally or written to a public official to express their views on global warming — remarkable levels of activism for a group that has not yet reached voting age.

The poll by the Post and Kaiser Family Foundation is the first major survey of teenagers’ views since the explosion of the youth climate movement last year. Inspired by Greta Thunberg, 16, whose yearlong “strike” in front of the Swedish Parliament and carbon-neutral sailboat voyage across the Atlantic have made her an activist icon, growing numbers of teens have been skipping school on Fridays to protest on behalf of something they say is more important.

This week, in the run-up to a major U.N. summit, ­hundreds of thousands of school kids plan to abandon their classrooms to demand more aggressive measures to protect the planet.

“People feel very guilty when a child says, ‘You are stealing my future.’ That has impact,” Thunberg told the Post. “We have definitely made people open their eyes.”

More than 7 in 10 teenagers and young adults say climate change will cause a moderate or great deal of harm to people in their generation, a slightly higher percentage than among those 30 and older. By the time today’s high schoolers turn 30, scientists say the world must achieve a “rapid and far-reaching” transformation of society to avoid warming’s most dire consequences.

Dire signs are here, teens say

Several teenagers said in interviews that they are already feeling its effects.

Gabe Lopez, 16, of Everett, Wash., said warming waters have taken a financial toll on relatives who fish in the Pacific. Graham, who lives in Silver Spring, Md., was inspired to take action after seeing hurricanes bombard Puerto Rico, North Carolina and the Bahamas — and watching floods repeatedly deluge her grandmother’s home in Ellicott City, Md.

“It’s like a dystopian novel,” she said. “To grow up seeing the world fall apart around you and knowing it’s going to be the fight of your lives to make people stop it.”

Both Lopez and Graham said thinking about climate change makes them afraid, an emotion they share with 57% of teens nationwide. Fewer than a third of teens say they are optimistic.

“A lot of it is connected to being a kid,” Lopez said. “We can’t vote. We don’t have anyone to represent us.”

Adults, he said, don’t seem to take the issue as seriously, or as personally, as people his age. Lopez recalled getting into an argument with his driving instructor after the older man was dismissive of students’ anxieties about ­climate change.

Adults “think: ‘Oh you’re so young, you don’t know what you’re talking about,’ ” he said. “But I know the facts, and I know what the most drastic consequences will be. I know that people aren’t doing what needs to be done.”