April 22 marks the 43rd observance of Earth Day in the United States. Organized by Sen. Gaylord Nelson (D-Wis.), the first Earth Day in 1970 saw an estimated 20 million Americans demonstrate in support of the environment. By 2012, over one billion people in 192 countries took part in Earth Day festivities.
Tracing its roots to the 19th century conservation movement, modern environmentalism -- and its accompanying protests -- has gained support since the first Earth Day, despite modest progress on the policy front. A number of U.S. lawmakers have tried repeatedly to advance bills aimed at protecting the environment and reducing carbon emissions, as the international community warns that global investments in clean energy may be progressing too slowly to limit the effects of climate change.
The second decade of the 21st century -– marked by America's largest oil spill, the hottest year on record for the continental U.S. and the bitterly divisive Keystone pipeline proposal -- has already confirmed the growing relevance of environmental issues in America.
From dramatically unfurled banners across world landmarks to a “toilet protest” and an underwater government cabinet meeting, the demonstrations captured in the images in the slideshow below reflect a spirit unlikely to wane.
This story appears in Issue 45 of our weekly iPad magazine, Huffington, in the iTunes App store, available Friday, April 19.