Every year 23rd March world meteorological day celebrate in the world.Although it's not so famous but still this day celebrate by World Meteorological Organization (WMO) because our biggest concern that World climate is changing and air pollution,water pollution and Global warming.We already know how lots of developed countries weather has been changing due to global warming because of too many industrialization(China & US the top two CO2 emitter country) without giving much importance to environment and that's why this days is symbolize to pollution free world in water,air,soil and also few others thing.

Finally this year(2009) theme is

Weather, climate and the air we breathe
Please see another thread

The Main Polluters