350.org

Co-founded in 2008 by author Bill McKibben and a group of university students, 350.org takes its name from the 350 parts-per-million safe upper limit for atmospheric CO2. It runs online campaigns, grassroots organizing, and mass mobilizations against fossil fuel projects and for renewable energy, and helped ignite the global fossil fuel divestment movement. Its network of volunteer organizers spans over 188 countries.