Greenhouse Effect: A* understanding for IGCSE Biology 4.12 4.13 4.14

The Greenhouse Effect is the name given to the way in which the earth’s atmosphere acts to warm up the planet.  The earth and the moon gain almost exactly the same incident radiation from the sun and yet average temperature on the earth is stable at around 14 degrees Celsius.  On the moon the temperature fluctuates wildly from 1oo degrees Celsius during the day to minus 153 degrees Celsius at night.   Life would be impossible in such extreme and variable conditions and so the greenhouse effect is definitely a “good thing” for life on our planet.

How does the greenhouse effect work?

Well the main idea here is that there are certain gases in the atmosphere that can trap the infrared radiation that the earth emits and prevent it escaping the atmosphere.  These greenhouse gases are warmed as they absorb the infrared and so the atmosphere heats up.

greenhouseeffectdiagram

Remember that because the sun is so hot, it emits radiation at a much higher frequency.  This is mostly in the “visible light” part of the spectrum together with some ultraviolet.  The gases in the atmosphere cannot trap visible light (air is transparent as you have probably noticed) and so most of the solar radiation passes through the atmosphere and hits the earth.

greenhouseeffect

Which gases can act as greenhouse gases?

The two most prevalent gases in the atmosphere are nitrogen (N2) and oxygen (O2) and neither is able to trap infrared so cannot act as a greenhouse gas.  The principle greenhouse gases in the atmosphere are

greenhouse-gases-most-common

  • carbon dioxide
  • water vapour
  • methane
  • ozone
  • nitrous oxide

So what’s the problem?

Well of course the problem is that human activities over the past century or so have altered the composition of the atmosphere so that the concentration of greenhouse gases has risen.  This has meant more heat is trapped and climate systems are altered in consequence.  This enhanced-greenhouse effect is the problem and I will look at this in the next post…..

total-heat-content

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