One problem with understanding why global warming is a very real possibility is that many people don’t have a basic understanding of the basic mechanisms by which molecules in the atmosphere absorb and re-emit radiation, adding to heating of the earth.  And infrared spectroscopy is not something covered in basic college educations, unless one majors in a hard science.  Besides a really nice animation, this site has excellent written explanation, reading, in part:

Absorption of Infrared Radiation by carbon dioxide happens because the carbon-oxygen bonds can stretch or flex at a frequency that allows them to absorb an infrared photon. There are a number of ways in which the molecule can oscillate. One type involves the bonds stretching and contracting like springs. The molecule can absorb an IR photon when this stretching is asymmetric. The alternative is for the bonds to flex as shown in this animation. The flexing movement allows absorption at a longer wavelength. … the oscillating molecule can then re-emit the infrared energy as a photon traveling in a random direction …

Check it out.