If William Ernest McKibben had not become a leader of the 21st-century global environmental movement, if he had perhaps been born 150 years ago, he would have made a great vicar. His middle name suits him. After talking to a digital moving picture of him on my computer, via Skype – he in his loft study on the edge of the Green Mountain National Forest in Vermont, with the first snow of the year on the ground outside, me in my loft at home in London – I came away determined to try harder to figure out if I can do more in my own life to help slow the increase in the level of carbon dioxide in the air.

McKibben travels all the time and says his own carbon footprint is "crazily high". But the campaigning organization he now heads, 350.org, is deliberately organised in such a way that most people campaign and organize as close to home as they can, using computers and telephones to talk to each other. When I suggest there are some things that can't be done so easily or so well electronically (a newspaper interview arguably being one of them), he laughs: "Well, we'd better start figuring out what we can do." By not flying 6,500 miles to Vermont and back to meet him, I have ducked responsibility for 1.5 tonnes of CO2.

Twenty-one years ago Bill McKibben wrote one of the first books about climate change. The End of Nature set out in detail the facts, as they then were, about the rapidly increasing concentration of greenhouse gases in the atmosphere, and passionately entreated its readers to pay attention.

"It is astonishing if you think about it that we knew 30 years ago what we needed to do, and we had much of the technology to do it," he says. "And we just walked away from it. On the list of bad mistakes human beings have made, that's right up there."

Not everyone made the same mistake. With a half-smothered chuckle, he describes how, on a visit to the headquarters of the Chinese solar energy giant Himin Solar earlier this year, he was shown one of the solar panels that Jimmy Carter installed on the White House roof in 1979, and which Ronald Reagan removed soon afterwards. A few weeks ago McKibben drove to Washington DC in a biodiesel-powered van with another of Carter's solar panels, salvaged from its retirement on the roof of a college cafeteria in Maine, to lobby President Obama to bring solar power back to the White House.

"They weren't all that keen to see us really. I think they were worried that these solar panels were somehow associated with Jimmy Carter, that they would catch some sort of electoral disease from touching them," he says. "But we kept saying 'no, don't worry, even people who don't know about global warming really like solar panels!' And they called us up three days before this big global work party [the 10/10/10 climate demonstrations], and said 'OK, we're putting them on in the spring'."

For the first 25 years of his career, McKibben was a writer. The son of journalists, and president while at university of the Harvard Crimson newspaper, he carved out a niche as a classy environmental reporter, publishing a book every few years. The Age of Missing Information contrasted the knowledge gleaned from cable TV over 24 hours with a day spent on a mountain. Maybe One tackled the controversial subject of human population – McKibben and his wife, the writer Sue Halpern, have one 17-year-old daughter, Sophie, who is founder-editor of a children's magazine. He wrote about hiking, skiing and genetic engineering, and an anti-consumerist essay about how to spend less than $100 on Christmas.

Full of clearly presented information, McKibben's books were also filled with description and feeling. He left New York, where his first job was writing for the New Yorker's Talk of the Town column, and moved first to the Adirondack mountains in upstate New York, and then to Vermont. He became a nature writer, devoted to finding meaning in landscape: "On the mountain, of course, death surrounds you always. Dead trees, the insects and the birds excavating their guts; dead leaves under your feet beginning to disintegrate with a year of rain and snow; dead bones in the woods."

He looked back at the work of earlier explorers, marveled at the joy of the American outdoors, "not the dark and forbidding wilderness of European fairy tales but a blooming, humming, fertile paradise". The British academic and author Robert Macfarlane recalls the impact of The End of Nature's "astonishing central idea, that the entire globe is post-natural, whether that be a sunset or the Arctic, everything bears our traces. Encountering that idea for the first time was incredibly powerful."

Environmental activism was always something that interested McKibben: his first book included a discussion of the radical ideas and direct action campaigns of Earth First! and other conservationists in the western US. But he was a writer: he and Halpern built their home on land once owned by the poet Robert Frost, whose own summer cabin is nearby, "so there's some good writing karma, and lots of trees".

"I think my assumption when I was 27 was that explaining rationally all the trouble we're in would be sufficient, and that politicians and whoever would act. I'm older now and I think I've come to understand a little more clearly that we're going to need to build some power if we're going to mount a serious challenge," he says.