Organizers call it "the most widespread day of environmental action in the planet's history." Today, in 181 countries and all 50 U.S. states, people are taking part in an event organized by 350.org.
The goal, the group says, is to bring attention to the need to lower carbon levels. In the Newsroom, we're explaining what the "350" means.
For facts and analysis about this issue and more, check out cnn.com/environment and our special section on "Eco Solutions."
Participating in the 350 event? What do you think about it?