Over the past few 100 years, human have been burning trees and fissile fuels
, thereby releasing millions of tones of carbon dioxide into the atmosphere. The increased level of carbon dioxide in the atmosphere has caused the temperature of the Earth to rise. This, in turn, causes more water to evaporate into the atmosphere. Water vapor is also very good at absorbing heat. This is causing the Earth's atmosphere to become even warmer. Scientist has called this effect Global Warming'. They have warned that Global Warming could shift rainfall patterns, raise the sea level and alter the ecological balance.