Monday, September 5, 2011

Greenhouse Effect and Greenhouse Gases

When thermal radiation is emitted from the earth some of it is trapped by gases in the atmosphere and then re-radiated back towards the earth.  This process is called the greenhouse effect and the gases which contribute to this process are called greenhouse gases.

Although this effect is necessary to warm the earth and therefore needed to sustain life, too much of the greenhouse effect causes the average temperature of the earth to rise.  This phenomenon is called global warming and occurs when the amount of greenhouse gas in the atmosphere is increased.  What are these greenhouse gases?  They are water vapor, carbon dioxide, methane, ozone, sulfur hexafluoride, hydrofluorocarbons, and perfluorocarbons.  Of those listed, the first four contribute significantly to the green house effect:



Where are these greenhouse gases coming from?  Although these gases have been produced naturally for billions of years, there has been an unprecedented increase in the last hundred years.  As seen in the graph below, the start of the increase of every greenhouse gas has coincided perfectly with the onset of the industrial revolution.  This is not a coincidence.  The increase in atmospheric greenhouse gas concentration is undeniably caused by humans.


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