WMO Greenhouse Gas Bulletin - No.6: The State of Greenhouse Gases in the Atmosphere Based on Global Observations through 2009

The report shows that the globally averaged mixing ratios of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) reached new highs in 2009, with CO2 at 386.8 ppm, CH4 at 1803 ppb and N2 O at 322.5 ppb. These values are greater than those in pre-industrial times (before 1750) by 38%, 158% and 19%, respectively. Atmospheric growth rates of CO2 and N2 O in 2009 are consistent with recent years, but are lower than in 2008. After nearly a decade of no growth, atmospheric CH4 has increased during the past three years. The reasons for renewed growth of atmospheric methane are not fully understood, but emissions from natural sources (from northern latitudes and the tropics) are considered potential causes. The NOAA Annual Greenhouse Gas Index shows that from 1990 to 2009, radiative forcing by all longlived greenhouse gases increased by 27.5%, with CO2 accounting for nearly 80% of this increase. The combined radiative forcing by halocarbons is nearly double that of N2O.