evidence: Water vapor is the most important GHG, since globally it is the most abundant of these gases, although it varies from 0-3% in a given location. NOAA's Carbon Cycle Greenhouse Gases (CCGG) group is concerned with the abundances of many of the other GHGs, since humans have a dominant role in the growing atmospheric concentrations of these gases. The gases measured by the CCGG include carbon dioxide (the second most important GHG), methane, nitrous oxide, sulfur hexafluoride, ozone, and a few others. While these gases constitute only a tiny fraction of Earth's very large atmosphere, their amounts are sufficient to absorb a major fraction of the infrared light in the atmosphere.