Explain how global warming takes place in the presence of green house gases. Give a reason why the surface temperature of earth is maintained in absence of green house gases.

The green house effect results in rise of atmospheric temperature which is not confined to one region but also has a global impact and is termed as global warming.

In absence of green house gases the surface temperature on earth is maintained since -

1. The solar radiations emitted as heat radiations, passes through the clear atmosphere.
2. It reaches the earth's surface where it is absorbed and retained.
3. Some of the absorbed heat radiations is reflected back into the atmosphere. [radiations from the earth takes place in two ways - reflected solar radiation and emitted thermal infra red radiations]

Thus, a balance is maintained between the heat energy absorbed by the earth and radiated from the earth.