Greenhouse Gases

The Greenhouse Effect

How do(es) carbon dioxide (and other greenhouse gases) cause warmer temperatures?  Sunlight comes through the atmosphere and when that happens, some of that sunlight is directly reflected into space (through ice in the poles) and some hits the ground.  When that happens some of the energy is absorbed in the ground, and then it reflects back into space with a different wavelength (in the infrared radiation part of the electromagnetic spectrum).  For that reflected energy in infrared part of the spectrum, some goes straight into space and some gets absorbed by certain gases called greenhouse gases.  When that energy gets absorbed, it gets trapped into our atmosphere and it warms our atmosphere.  This phenomenon is not a bad thing inherently; in fact, it is necessary for our survival.  Without it, the Earth’s temperature would plummet.  However, too much of it can also be a bad thing, because it causes the Earth to warm too much.

But, why are certain gases greenhouse gases, but not others?  Certain molecules are nonpolar (meaning that the electron density is equally distributed throughout the molecule) but through vibrations in the molecule, it can become polar momentarily.  However, some molecules cannot do this.  For example, CO2 and H2O can vibrate in many different ways, but gases like N2, which only have two atoms, cannot vibrate in the same ways:

Screen Shot 2014-04-07 at 10.35.47 PM

Gases with only two atoms cannot do these vibrations.

The energy from that infrared radiation that is being reflected from the ground gets absorbed by these gases only because it causes them to vibrate, causing the molecule to become polar from nonpolar or nonpolar from polar (this essentially just means that the electrons, as the molecule vibrates, become unequally distributed throughout the molecule).  This causes the molecule to gain kinetic energy and vibrate, absorbed the heat.  More carbon dioxide in the atmosphere would cause more infrared radiation to be absorbed by these molecules, causing more heat to be retained in the atmosphere.

Watch out for a post about the evidence for climate change coming soon!

Works Cited


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