World Environment Day (WED) is observed to stimulate awareness of the environment and enhance political attention and public action. It is on june-5.

It was the day that united-nations-conference-on-the-human-environmentbegan. The United Nations Conference on the Human Environment was from 5-16 June 1972. It was established by the united-nations-general-assemblyin 1972. The first World Environment Day was observed in 1973. World Environment Day is hosted every year by a different city with a different theme and is commemorated with an international exposition on the week that 5th June is on. World Environment Day is in summerin the northern-hemisphereand winterin the southern-hemisphere.

Source: Wikipedia