Page 340 - New Medley 5 Semester 1

The Polar Zone

The Polar Zone is also known as the Frigid Zone. It also lies in both

the hemispheres. In the Northern Hemisphere, it extends from the Arctic

Circle to the North Pole and in the Southern Hemisphere, from the
Antarctic Circle to the South Pole. This region receives very little heat

from the sun and, therefore, this region remains cold throughout the

year. Here temperature always remains below zero degrees (0°). This is
the coldest part of the Earth.

Global Warming

Recently, it has been noticed that the mean temperature of the Earth

and of the atmosphere is increasing due to Greenhouse Effect, which is

causing Global Warming. The average increase of the temperature on
the Earth and also in the atmosphere is one degree in the last 100 years.

The main greenhouse gases are carbon dioxide, methane and CFCs
(Chlorofluorocarbons). The increase of the greenhouse gases in the

atmosphere is due to pollution, which is caused by nature and the activities

of human beings. These gases can easily trap the heat of the Sun, and
this is called the Greenhouse Effect.

Carbon dioxide is added in the atmosphere by the burning of wood, coal

and petroleum. It is also added by vehicles and industries. Methane gas
is added in the atmosphere by the digestive system of the herbivores,

such as cows, horses, goats and sheep. CFCs are released from perfume
and deodorant sprays. CFCs are also used in refrigerators.

Let us try to understand how the trapped gases in the atmosphere cause

warming and increase of temperature. Suppose you are sitting inside
a car and the windows are closed. The rays of the sun fall on the car.

Some of them pass through the windshield of the car. The heat collected
inside the car cannot fully escape through the windshield. This causes

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