Biology GREEN HOUSE EFFECT

### KEY TOPICS

star Greenhouse Effect
star Action of Greenhouse Gases
star Global Warming

### GREENHOUSE EFFECT

● The term color{brown}("‘Greenhouse effect’") has been derived from a color{violet}("phenomenon") that occurs in a color{violet}("greenhouse. ")

● A color{violet}("Greenhouse") looks like a color{violet}("small glass house") and is used for color{violet}("growing plants") especially during winter.

● In a color{violet}("greenhouse") the color{violet}("glass panel") lets the color{violet}("light") in, but does not allow heat to escape.

● Therefore, the color{violet}("greenhouse warms") up, very much like inside a color{violet}("car") that has been parked in the color{violet}("sun") for a few hours.

● The color{violet}("greenhouse effect") is a naturally occurring phenomenon that is responsible for color{brown}("heating of Earth’s surface") and color{violet}("atmosphere.")

● Without color{violet}("greenhouse effect") the color{violet}("average temperature") at color{violet}("surface of Earth") would have been a color{brown}("chilly" –18^o C) rather than the present color{brown}("average of" 15^oC).

### ACTION OF GREEN HOUSE GASES

● In order to understand the color{violet}("greenhouse effect"), it is necessary to know the color{violet}("fate") of the color{violet}("energy of sunlight") that reaches the outermost atmosphere.

● color{violet}("Clouds and gases reflect") about color{violet}("one-fourth") of the incoming color{violet}("solar radiation"), and color{violet}("absorb") some of it but almost half of incoming color{violet}("solar radiation") falls on color{violet}("Earth’s surface heating") it, while a small proportion is reflected back.

● color{violet}("Earth’s surface re-emits heat") in the form of color{violet}("infrared radiation") but part of this does not escape into space as color{violet}("atmospheric gases") (e.g., carbon dioxide, methane, etc.) absorb a major fraction of it.

● The molecules of these color{violet}("gases radiate heat energy"), and a major part of which again comes to color{violet}("Earth’s surface"), thus color{violet}("heating") it up once again.

● This cycle is repeated many a times.

● The above-mentioned gases – color{brown}("carbon dioxide and methane") – are commonly known as color{brown}("greenhouse gases") because they are responsible for the color{violet}("greenhouse effect")

### GLOBAL WARMING

● Increase in the level of color{violet}("greenhouse gases") has led to considerable color{violet}("heating of Earth") leading to global warming.

● During the past century, the color{violet}("temperature of Earth") has increased by color{violet}(0.6^oC), most of it during the last three decades.

● Scientists believe that this color{violet}("rise in temperature") is leading to deleterious changes in the color{violet}("environment") and resulting in color{violet}("odd climatic changes") (e.g. color{brown}(" El Nino effect")), thus leading to increased melting of polar ice caps as well as of other places like the Himalayan snow caps.

● Over many years, this will result in a color{violet}("rise in sea level") that can submerge many coastal areas.

● The total color{violet}("spectrum of changes") that global warming can bring about is a subject that is still under active research.

● We can color{violet}("control global warming") by various measures.

● The measures include cutting down use of color{brown}("fossil fuel"), color{violet}("improving efficiency") of energy usage, reducing
deforestation, planting trees and slowing down the growth of human population.

● International initiatives are also being taken to color{violet}("reduce the emission") of greenhouse gases into the atmosphere.