Question

The reason for global warming is

• A. Long wavelength radiation are absorbed by the atmosphere
• B. Short wavelength radiation are absorbed by the atmosphere
• C. Atmosphere traps radiations to increase the temperature
• D. UV and infra red radiations

Answer 1

Answer: (A)

Long wavelength radiation are absorbed by the atmosphere

The earth receives energy from the sun in the form UV (ultraviolet), visible, and near-IR (infrared) radiation, most of which passes through the atmosphere without being absorbed. Of the total amount of energy available at the top of the atmosphere, about 50% is absorbed at the earth's surface. Because it is warm, the surface radiates far IR thermal radiation, that consists of wavelengths that are predominantly much longer than the wavelengths that were absorbed. Most of this thermal radiation is absorbed by the atmosphere and re-radiated both upwards and downwards; that radiated downwards is absorbed by the earth's surface. This trapping of long-wavelength thermal radiation leads to a higher temperature than if the atmosphere were absent. The increase in the level of greenhouse gases has led to considerable heating of earth leading to global warming.