Amount varies geographically


Most abundant greenhouse gas, not most efficient absorber







Yearly variations due to biological effects

in spring/summer huge quantities are removed by photosynthesis (fixed carbon)

fall/winter fixed carbon released during biological decay of plant material













The concentration of CO2 in the atmosphere is sufficient to almost completely absorb the IR radiation in several spectral regions

Additional CO2 does not remove much more IR radiation

Methane absorptions occur in spectral regions where little IR absorption is occurring

Each new methane molecule provides can absorb IR radiation