William Ernest McKibben (born December 8, 1960)[1] is an American environmentalist, author, and journalist who has written extensively on the impact of global warming.

He has authored a dozen books about the environment, including his first, The End of Nature (1989), about climate change, and Falter: Has the Human Game Begun to Play Itself Out?

[6] In 2011 and 2012 he led the environmental campaign against the proposed Keystone XL pipeline project[7] and spent three days in jail in Washington, D.C. Two weeks later he was inducted into the literature section of the American Academy of Arts and Sciences.

[11] In 2010, The Boston Globe called him "probably the nation's leading environmentalist"[12] and Time magazine book reviewer Bryan Walsh described him as "the world's best green journalist".

[21] McKibben began his freelance writing career at about the same time that climate change appeared on the public agenda following the hot summer and fires of 1988 and testimony by James Hansen before the United States Senate Committee on Energy and Natural Resources in June of that year.

[22] His first contribution to the debate was a brief list of literature on the subject and commentary published December 1988 in The New York Review of Books and a question, "Is the World Getting Hotter?

Described by Ray Murphy of the Boston Globe as a "righteous jeremiad," the book excited much critical comment, pro and con; was for many people their first introduction to the question of climate change;[25] and the inspiration for a great deal of writing and publishing by others.

It is an account of an experiment in which McKibben collected everything that came across the 100 channels of cable TV on the Fairfax, Virginia, system (at the time among the nation's largest) for a single day.

[27][28] Subsequent books include Hope, Human and Wild, about Curitiba, Brazil, and Kerala, India, which he cites as examples of people living more lightly on the earth; The Comforting Whirlwind: God, Job, and the Scale of Creation, which is about the Book of Job and the environment; Maybe One, about human population; Long Distance: A Year of Living Strenuously, about a year spent training for endurance events at an elite level; and Enough, about what he sees as the existential dangers of genetic engineering and nanotechnology.

We Are Better Together is a picture book for children celebrating the power of human cooperation and the beauty of life on Earth, illustrated by artist Stevie Lewis.

The Flag, the Cross, and the Station Wagon: A Graying American Looks Back at His Suburban Boyhood and Wonders What the Hell Happened is a personal memoir that also digs into America's history to reflect on what has brought us to the present environmental crisis.

Beginning in January 2007, he founded Step It Up 2007, which organized rallies in hundreds of American cities and towns on April 14, 2007, to demand that Congress enact curbs on carbon emissions by 80 percent by 2050.

The organizing effort, aimed at the entire globe, drew its name from climate scientist James E. Hansen's contention earlier that winter that any atmospheric concentration of carbon dioxide (CO2) above 350 parts per million was unsafe.

[36] On October 24, 2009, it coordinated more than 5,200 demonstrations in 181 countries, and was widely lauded for its creative use of internet tools, with the website Critical Mass declaring that it was "one of the strongest examples of social media optimization the world has ever seen.

[25] In September 2021, McKibben launched Third Act, a group and campaign for climate change activists aged 60 or older, hoping to leverage the demographic's free time and accumulated assets for political pressure on government.

[47] In 2016, McKibben wrote in The New York Times that he is "under surveillance" by "right-wing stalkers" who photograph, pursue, and inquire about him and members of his family in search of ostensible instances of environmental hypocrisy.

[49] In December 2019, along with 42 other leading cultural figures, McKibben signed a letter endorsing the British Labour Party under Jeremy Corbyn's leadership in the 2019 general election.

The letter stated that "Labour's election manifesto under Jeremy Corbyn's leadership offers a transformative plan that prioritizes the needs of people and the planet over private profit and the vested interests of a few.