Bill McKibben is a Vermont author and environmentalist. The book he’s most known for, “The End of Nature,” was the first to introduce climate change to a general audience.

McKibben, photographed during an unseasonably warm winter, lives on Vermont land once owned by poet Robert Frost.

McKibben was one of 1,252 environmentalists arrested during late-summer protests in the nation’s capital.

Ahead of this November 6, 2011, protest, McKibben asked supporters to surround the White House in a “giant hug.”

Activists protest the Keystone XL pipeline in September 2011, two months before McKibben helped derail the controversial project.

McKibben, who can still look uncomfortable in the spotlight, addresses a crowd.

In 2009, people in 181 countries showed their support for a 350 parts per million carbon dioxide target. Here, Cape Town.

Mount Kilimanjaro, Tanzania.

Lebanon

Trujillo, Peru

Sandpoint, Idaho

Sydney

Shanghai, China

Okavango Delta, Botswana

India

Belgrade, Serbia

Paris

Mexico City

Afghanistan

Koprivnica, Croatia

Dhaka, Bangladesh

Hollywood

Debieh, Lebanon

Great Barrier Reef, Australia

Stellenbosch, South Africa

McKibben speaking in Times Square in New York City