Volunteers collect garbages to mark the World Earth Day in Panama City, capital of Panama, on April 22, 2017. (Xinhua/Mauricio Valenzuela)

Volunteers collect garbages to mark the World Earth Day in Panama City, capital of Panama, on April 22, 2017. (Xinhua/Mauricio Valenzuela)

The Canadian National Tower (CN Tower) is lit up in green to celebrate the 2017 Earth Day in Toronto, Canada, April 22, 2017. (Xinhua/Zou Zheng)