When Greta Browne began her trek up the Eastern seaboard in March to attract attention to climate change, the grandmother of three envisioned crowds of supporters à la Forrest Gump.

Instead, it was a sometimes lonely road for the retired Unitarian minister, who logged some 1,200 miles by foot by the time her journey ended Aug. 29. Making her way from New Orleans to Rouses Point, N.Y., the white-haired Browne wore T-shirts emblazoned with the slogan “Walking for the Climate.” She made her case to drivers who stopped alongside her on the road, spoke at churches along the way and blogged regularly, dedicating her musings to her grandchildren.

“Sometimes, you just have to stand up,” she said, by way of explaining the project.

It all started last year, when she joined an environmental group and read Six Degrees: Our Future on a Hotter Planet by Mark Lynas. The book predicts humanity’s demise by the end of the century if temperatures on Earth continue to rise. Browne said she thought of her grandchildren and became heartsick. She pledged to do something, she wrote on her blog, “Because it seemed absurd to go on as usual.”

To be sure, Browne is not the first activist to promote environmental causes through stunts. Writer Colin Beavan lived (somehow) without toilet paper and electricity for a year when he “went off the grid” in New York City. British “eco-adventurer” David de Rothschild has built a boat from reused plastic water bottles and plans to sail from San Francisco to Sydney, Australia. Browne’s own role model was Dorris Haddock, or Granny D, who was 90 years old when she walked across the country lobbying for campaign finance reform in 1999.

Browne said her carbon footprint is about half that of the average American. One exception was her home during the walking campaign: a 1982 van that she called a “disgusting gas guzzler.”

Still, she plodded along undaunted.

About 500 to 1,000 cars passed her on the road each day, she estimated, and about 1 percent honked or gave her a thumbs-up sign. During her travels, she met one woman at a church who said, “Oh, you are preaching to the choir. We already recycle.”

Browne said she remembers thinking that was “so 1980s.” People need to do more, she said. “People just don’t see enough urgency to change their life."