WMO Greenhouse Gas Bulletin - No.4: The State of Greenhouse Gases in the Atmosphere Using Global Observations through 2007

The latest analysis of data from the WMO-GAW Global Greenhouse Gas Monitoring Network, a comprehensive network of the Global Climate Observing System (GCOS), shows that the globally averaged mixing ratios of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) have reached new highs in 2007 with CO2 at 383.1 ppm, CH4 at 1789 ppb and N2 O at 320.9 ppb. These values are higher than those in pre-industrial times (before 1750) by 37%, 156% and 19%, respectively. Atmospheric growth rates in 2007 of CO2 and N2 O are consistent with recent years. The mixing ratio of CH4 shows the largest increase since 1998. The NOAA Annual Greenhouse Gas Index (AGGI) shows that from 1990 to 2007 the atmospheric radiative forcing by all long-lived greenhouse gases has increased by 24.2%. The combined radiative forcing by the most abundant ozone depleting substances, CFC-11 and CFC-12, exceeds that of N2O. They are decreasing very slowly as a result of emission reductions under the Montreal Protocol on Substances That Deplete the Ozone Layer.