Ever since humans started the industrial revolution and the burning of fossil fuel like coal and oil and natural gas, the carbon dioxide concentration in the atmosphere has been increasing. This leads to the more efficient trapping of the Suns energy and heating of the atmosphere and oceans.

Although the heating of earth due to greenhouse effect is beyond questioning the magnitude of the effect is still a bit uncertain. Most experts believe that we will see +2-+5 deg C of warming in next 50 years. This has some very serious consequences.

Greenhouse effect is what has driven the warming of Earth over past 50-100 yrs.