Every year on 5th June, World Environment Day is celebrated in over 100 countries. It was first held in 1974 by the United Nation, since then, it has been an important campaign to fight against the increasing global warming as well as emerging environmental risks from the human population, marine pollution etc.
Similarly, the themes vary from year to year. Last year, the theme for World Environment Day 2021 is “Ecosystem Restoration”.
You can read the details about it on https://www.genevaenvironmentnetwork.org/world-environment-day/