Earth Day - April 22nd
 

from the Earth Day Website:

Earth Day Network was founded on the premise that all people, regardless of race, gender, income, or geography, have a moral right to a healthy, sustainable environment. Our mission is to broaden and diversify the environmental movement worldwide, and to mobilize it as the most effective vehicle for promoting a healthy, sustainable environment. We pursue our mission through a combination of education, public policy, and consumer activism campaigns. Our campaign and programs are predicated on the belief that an educated, energized population will take action to secure a healthy future for itself and its children. Earth Day Network has a global reach with a network of more than 17,000 partners and organizations in 174 countries. More than 1 billion people participate in Earth Day activities, making it the largest secular civic event in the world.

Details here:
http://www.earthday.net/