Atmosphere And Weather

The Greenhouse Effect



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Greenhouse effect is the process where emissions of infrared radiation from other sources(e.g The Sun) or the atmosphere warms a planet's surface. It comes from the analogy of internal warming of a greenhouse as compared to external heat.



Basic mechanism:

Earth receives energy from the sun mainly through radiation as conduction and convection is not possible through the vacuum conditions of outer space. The Earth primarily reflects 30% of the incoming radiation through the clouds and land masses. The remaining of about 70% is absorbed to warm the land, atmosphere and oceans. In most cases, the infrared that are not absorbed by the surface are absorbed by greenhouse gases and clouds and thus unable to escape to space. For the earth to be at a constant state of temperature, the Earth does not gain or lose heat rapidly, thus the reflection and absorption should be rather constant through infrared radiation.

Cloud cover is generally one of the mechanisms for greenhouse effect because of it capability to trap and at the same time reflect infrared radiation. Clouds are generally white in color and as everyone knows, white objects are bad conductors but good radiators, they are therefore good reflectors and bad absorbers. Yet in the situation of greenhouse effect, they aid in reflecting and absorbing due to its nature. Incoming radiation are mostly reflected by cloud cover, and those that get in are kept in due to cloud cover, which explains why in some areas of the earth, there are major temperature ranges and in come near constant temperatures.

In deserts, in the day, due to lack of evaporation, cloud cover is low, and thus most of the radiation reaches the ground causing the temperature to rise rapidly. Yet at night, due to the lack of cloud cover, radiation escapes rapidly causing the rapid fall to extreme low temperatures at night.

Yet in the tropics, temperature ranges are not too extreme. High evaporation allows good cloud cover, as most of the heat are either reflected or absorbed, the temperature reaches a certain amount. And at night, cloud cover is still evident to regulated the heat within the area and thus does not promote the extremes of temperature ranges.



Greenhouse gases:

Common gases that causes greenhouse effects are H2O (36%), CO2 (12%), O3 (3%).
These gases though not the major gases in the atmosphere as compared to oxygen and nitrogen are good absorbers due to their quantum make-up.
These gases have a linear arrangement, thus allowing them to interfere with the electron configurations, due to such a cases, infrared radiation can be absorbed and making the molecules more excited. And since H20 is common everywhere due to evaporation, they contribute the most to the effect.



Positive feedback and runaway greenhouse effect:

Positive feedback happens when there is an increase in greenhouse gases, as gases absorb more heat, it causes an increase in evaporation which forms H2O gases, which in turn contribute to more greenhouse effect, causing an increased amount of warming through the effect. This is the situation the earth is in now, as heat continues to be accumulated, the world is in fact warming up causing problems like melting ice caps that could cause the submerging of low-lying coastal areas.

Runaway feedback happens when greenhouse gases decreases, causing the cooling of the earth and thus changing of states of matter to less excited stages, such a situation my lead to the freezing up of some greenhouse gases and thus will lead to even more cooling which is one of the primary works when ice ages happen.



Climate change:
As temperature of the area affects the climate system, greenhouse effects will affect the climate as the area turns warmer or cooler, and in present case, warmer, due to global warming. The greenhouse effect may be the main contributor and thus people should start taking action to stop the effect from causing the extreme warm up of the earth and leading to the end of life on earth.




References:
http://en.wikipedia.org/wiki/Greenhouse_effect

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