WMO Greenhouse Gas Bulletin - No.5: The State of Greenhouse Gases in the Atmosphere Using Global Observations through 2008

The latest analysis of observations from WMO's Global Atmosphere Watch (GAW) Programme shows that the globally averaged mixing ratios of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) have reached new highs in 2008 with CO2 at 385.2 ppm, CH4 at 1797ppb and N2 O at 321.8ppb: higher than those in pre-industrial times (before 1750) by 38%, 157% and 19%, respectively. Atmospheric growth rates of CO2 and N2 O in 2008 are consistent with recent years. The increase in atmospheric CH4 was 7ppb from 2007 to 2008, similar to the increase of the year before. These are the largest increases since 1998. The NOAA Annual Greenhouse Gas Index (AGGI) shows that from 1990 to 2008 the radiative forcing by all long-lived greenhouse gases has increased by 26.2%. The combined radiative forcing by halocarbons is nearly double that of N2O. Some halocarbons are decreasing slowly as a result of emission reductions under the Montreal Protocol on Substances That Deplete the Ozone Layer, whereas others are increasing rapidly.