In the years that followed, climate policy became an afterthought, then a partisan issue, then a casualty of the Republican Party’s delirious embrace of industry propaganda and self-delusion — until now, when it has become a matter of life and death.

Claudine Schneider recently told me that she was “grateful” to the Green New Deal for “raising the level of dialogue.” She is enthusiastic about the opportunity for the new House Select Committee on the Climate Crisis to hold public hearings, for the education not only of the public but also of members of Congress.

“The current Republicans, with their lies, denial of science, denial of the truth, do not deserve to be in office,” she said. “Pragmatism has to be the guiding light. When it comes to climate, the only pragmatic choice for the nation’s economy and the planet is to act now.”

Timothy Wirth shares her enthusiasm about the Green New Deal. The turning point in the public conversation, Mr. Wirth believes, came after the midterm election when students from the Sunrise Movement staged a protest in Nancy Pelosi’s office to demand a Green New Deal. Ms. Ocasio-Cortez joined them, giving a passionate speech in their defense.

“That was the catalytic moment,” Mr. Wirth told me. “It changed the emotion. It made you think, ‘Wow, we’re going to do this.’ It made you think that this time was different.”

This time is different. The Green New Deal, and the youth movement that helped produce it, has absorbed a critical lesson from the past 40 years of failed efforts to advance climate policy. Until now, activists and politicians have offered, over and over again, versions of the same argument: The science is clear; we know what we have to do; the longer we wait, the worse it will be for us; it’s foolish not to act.

You can find this argument in a 1979 report sent to President Jimmy Carter by four of the nation’s pre-eminent earth scientists warning that the disruptions from climate change “are sufficiently great to warrant the incorporation of the CO₂ problem into all considerations” of energy policy ; in the 1988 congressional hearing when Gus Speth, president of the World Resources Institute, said that “responsible” leaders “have no choice but to treat this threat as a real one, as an urgent threat, as one requiring serious responses, serious policy changes, and changes not in the distant future but in the near term”; and in 2006, in “An Inconvenient Truth,” when Al Gore wrote that “unless we take quick action the consequences for our planetary home could become irreversible.”