Switch off lights you don´t need.
Greenhouse gases are naturally present in the atmosphere and mantain temperatures on Earth that are favorable to life. Too much greenhouse effect, however, leads to warming of the global climate. In a century, world energy demand (used electricity, heating, and transportation, for example) has increased twenty fold. If current trends continue unabated, the world´s energy consumption willdouble by 2030.
Most of this energy comes from oil, gas, and coal, which produce greenhouse gases.
Make a point of switching off lights that do not need to be on, especially when you leave a room, and try to use daylight instead wherever possible. The less electricity is used, the less energy is needed, and therefore less greenhouse gas is pumped into the atmosphere.