Greenhouse Gases...  
increase the absorption of radiant heat
 

Gas

1978 2005  % increase
carbon dioxide            CO2 337 ppm 375 ppm 11.3 %
methane                      CH4 1.54 ppm 1.85 ppm 20 %
nitrous oxide               N2O 302 ppb 319 ppb 5.6 %
chloroflurocarbons      CF4 40 ppt 80 ppt 50 %
sulfur hexaflourides    SF6 0 ppt 5.21 ppt 521 %

 reference - Current Greenhouse Gas Concentrations