350.org was founded in 2008 by a group of university friends in the United States along with author Bill McKibben, who wrote one of the first books on global warming for the general public. The goal was to build a global climate movement. 350 was named after 350 parts per million — the safe concentration of carbon dioxide in the atmosphere.
350.org is an international environmental organization addressing the climate crisis. Its stated goal is to end the use of fossil fuels and transition to renewable energy by building a global, grassroots movement.
The 350 in the name stands for 350 ppm (parts per million) of carbon dioxide, which has been identified as the safe upper limit to avoid a climate tipping point. As of 2019, the current level has reached 415 ppm.
Through online campaigns, grassroots organizing, mass public actions, and collaboration with an extensive network of partner groups and organizations, 350.org has mobilized thousands of volunteer organizers in over 188 countries. It is one of the many organizers of the Global Climate Strike from September 20 to 27, 2019 which evolved from the Fridays for Future movement.