beginning of spring (UK)
22 - World Day for Water
22 – UN Earth Day
22 – US Earth Day http://www.earthday.org/
22 - World Biodiversity Day http://www.cbd.int/idb/2011/ (every 2 years)
5 – World Environment Day http://www.unep.org/wed/2009/english/content/about.asp
8 – World Oceans Day http://worldoceansday.org/
21 - summer solstice. The summer solstice occurs exactly when the Earth’s semi-axis in a given hemisphere is most inclined towards the sun, at its maximum tiltof 23° 26′. Though the summer solstice is an instant in time, the term is also colloquially used like Midsummer to refer to the day on which it occurs.
11 - World Population Day
: beginning of winter.
21 or 22 December: *Winter solstice : The winter solstice occurs exactly when the axial tilt of a planet is farthest away from its star, depending on the polar hemisphere of reference. Earth’s maximum axial tilt to our Sun during a solstice is 23° 26′. More evidently from high latitudes, a hemisphere’s winter solstice occurs on the shortest day and longest night of the year, when the sun’s daily maximum position in the sky is the lowest. Since the winter solstice lasts only a moment in time, other terms are often used for the day on which it occurs, such asmidwinter, the longest night or the first day of winter.