Biodiversity, Conservation and Environmental Issues — BIOLOGY STD 12 Science — Question

1. Greenhouse effect is caused due to heating up of earth’s surface and atmosphere. This heating is due to trapped infrared rays that are reflected from the earth’s surface by atmospheric gases.

2. The solar energy reaches the earth in the form of ultraviolet radiations, visible light and infrared and radio waves. Clouds and gases reflect about Vith radiations and absorb some of it.

3. Harmful UV radiations are absorbed by the ozone layer of the stratosphere and thus do not reach the earth’s surface.

4. Infrared radiation has heating effect thus it warms up the earth’s atmosphere and various objects. A part of the infrared radiations falling on the earth surface which have longer wavelength is reflected back into the outer space.

5. But there is a layer of carbon dioxide in the lower region of the atmosphere along with other atmospheric gases such as methane, nitrogen oxide, etc.

6. Due to these gases radiations cannot escape out. Carbon dioxide, along with methane, nitrogen oxides and CFCs can absorb infrared radiations reflected from the earth’s surface. They are therefore called greenhouse gases.

7. The blanket of these greenhouse gases in the atmosphere traps the reflected infrared rays and produces heat on the earth’s surface. This results in greenhouse effect which in turn causes global warming.