|Changes in atmospheric radiative forcing by long-lived greenhouse gases and the 2005 NOAA Annual Greenhouse Gas Index (AGGI). Click to enlarge.|
In 2005, the globally averaged concentrations of the greenhouse gases carbon dioxide (CO2) and nitrous oxide (N2O) reached new highs with CO2 at 379.1 parts per million (ppm)—up 0.53% from 377.1 ppm in 2004—and N2O at 319.2 parts per billion (ppb), according to the 2005 Greenhouse Gas Bulletin, published by the World Meteorological Organization (WMO).
Methane (CH4) concentrations were unchanged at 1,783 ppb. These values are higher than those in pre-industrial times by 35.4%, 18.2% and 154.7%, respectively. After water vapor, carbon dioxide, methane (CH4) and nitrous oxide (N2O) are respectively the three most prevalent greenhouse gases in the Earth’s atmosphere.
The recently introduced NOAA Annual Greenhouse Gas Index (AGGI) shows that from 1990 to 2005 the atmospheric radiative forcing by all long-lived greenhouse gases has increased by 21.5%. The AGGI increased by 1.25% from 2004 to 2005.
Radiative forcing is the change in the balance between radiation coming into the atmosphere and radiation going out. A positive radiative forcing tends on average to warm the surface of the Earth, and negative forcing tends on average to cool the surface.
The 35.4% rise in carbon dioxide since the late 1700s has largely been generated by emissions from the combustion of fossil fuels. Around one third of N2O discharged into the air is a result of human activities such as fuel combustion, biomass burning, fertilizer use and some industrial processes.
Human activity such as fossil fuel exploitation, rice agriculture, biomass burning, landfills and ruminant farm animals account for some 60% of atmospheric CH4, with natural processes including those produced by wetlands and termites responsible for the remaining 40%.
Accurate atmospheric observations from some 44 WMO Members are archived and distributed by the World Data Centre for Greenhouse Gases (WDCGG), located at the Japan Meteorological Agency.
WMO prepares the Greenhouse Gases Bulletin in cooperation with WDCGG and the Global Atmosphere Watch Scientific Advisory Group for Greenhouse Gases with the assistance of the National Oceanic and Atmospheric Administration's Earth System Research Laboratory.