The 50th anniversary of the first Earth Day was celebrated 50 years later, in 2020. Since the inaugural April 22 observance took place in 1970, the anniversary calculation is 2020 minus 1970, which equals 50.
Earth Day 2020 marked five decades since the nationwide environmental teach-in organized by Senator Gaylord Nelson and coordinated by Denis Hayes. The original event brought environmental issues into public debate across the United States, with activities at schools, universities, and hundreds of communities. Around 20 million Americans were estimated to have participated in 1970.
The anniversary year was historically unusual because the COVID-19 pandemic disrupted many planned in-person events. Earth Day organizations moved a substantial portion of the program online, using livestreams, digital education, citizen-science projects, and climate advocacy. Even with those changes, the 50th anniversary drew worldwide attention; more than 100 million people were reported to have observed Earth Day in 2020.
The 50th anniversary is sometimes confused with Earth Day’s 50th annual observance, but in this case the year count is straightforward: the first event was in 1970 and its half-century anniversary was in 2020.