世界地球日（Earth Day）即每年的4月22日，是一个专为世界环境保护而设立的节日，旨在提高民众对于现有环境问题的意识，并动员民众参与到环保运动中，通过绿色低碳生活，改善地球的整体环境。
Earth Day is the name given to two different annual observances that are intended to raise awareness about a wide range of environmental issues and problems and to inspire people to take personal action to address them.

Except for that general goal, the two events are unrelated, even though both were founded about a month apart in 1970 and both have gained wider acceptance and popularity ever since.

The First Earth Day

In the United States, Earth Day is celebrated by most people on April 22, but there is another celebration that predates that one by approximately a month and is celebrated internationally.

The first Earth Day celebration took place on March 21, 1970, the vernal equinox that year. It was the brainchild of John McConnell, a newspaper publisher and influential community activist who proposed the idea of a global holiday called Earth Day at a UNESCO Conference on the Environment in 1969.

McConnell suggested an annual observance to remind people of their shared responsibility as environmental stewards. He chose the vernal equinox—the first day of spring in the northern hemisphere and the first day of autumn in the southern hemisphere—because it is a day of renewal.

At the vernal equinox (always March 20 or March 21), night and day are the same lengths everywhere on Earth. McConnell believed that Earth Day should be a time of equilibrium when people could put aside their differences and recognize their common need to preserve Earth’s resources.

On February 26, 1971, U.N. Secretary-General U Thant signed a proclamation saying that the United Nations would celebrate Earth Day annually on the vernal equinox, thereby officially establishing the March date as the international Earth Day.