Latest WMO GHG Bulletin Now Available

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Executive summary

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 1797 ppb and N2O at 321.8 ppb: higher than those in pre-industrial times (before 1750) by 38%, 157% and 19%, respectively. Atmospheric growth rates of CO2 and N2O in 2008 are consistent with recent years. The increase in atmospheric CH4 was 7 ppb 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.

Overview

This is the fifth in a series of WMO-GAW Annual Greenhouse Gas Bulletins. Each year, they report the global consensus on the latest changes and atmospheric burdens of the most important, long-lived greenhouse gases: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), CFC-12 and CFC-11, as well as a summary of the contributions of the lesser gases.

Water vapour is the most important greenhouse gas, but it is connected to human activities only through climate feedbacks. This Bulletin focuses on those greenhouse gases that are directly influenced by humans and that are generally much longer lived in the atmosphere than water vapour. The three primary greenhouse gases are not only closely linked to anthropogenic activities, but also have strong interactions with the biosphere and the oceans. Chemical reactions in the atmosphere affect their abundances as well. Prediction of the evolution of greenhouse gases in the atmosphere requires an understanding of their many sources and sinks.

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Radiative forcing



According to the NOAA Annual Greenhouse Gas Index (AGGI), the total radiative forcing by all long-lived greenhouse gases has increased by 26.2% since 1990 and by 1.3% from 2007 to 2008 (see Figure 2). Five major gases (carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), CFC-12 and CFC-11) contribute about 96% of the increase in radiative forcing due to long-lived greenhouse gases that has occurred since 1750.

(*) This sign shows, that the percentage is calculated as the relative contribution of the mentioned gas to the increase in global radiative forcing caused by all longlived greenhouse gases since 1750.

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Carbon Dioxide (CO2)

CO2 is the single most important human-emitted greenhouse gas in the atmosphere, contributing 63.5 % (*) to the overall global radiative forcing. However, it is responsible for 85% of the increase in radiative forcing over the past decade and 86% over the last five years. For about 10,000 years before the industrial revolution, the atmospheric abundance of CO2 was nearly constant at ~ 280ppm (ppm = number of molecules of the gas per million molecules of dry air). This abundance represented a balance between the atmosphere, the oceans and the biosphere.



Monthly means of CO2 mixing ratios are shown on the plot (Figure 3, click to enlarge). The graph shows a substantial increase of the mixing ratio at all reporting stations.

CO2 measured on Mauna Loa constitutes the longest record of direct measurements in the atmosphere. The dark curve behind the monthly means represents the seasonally adjusted data. The amount of CO2 in the atmosphere is increasing exponentially at a rate of about 0.5% per year.

Data courtesy of Scripps Institution of Oceanography, University of California, San Diego and National Oceanic and Atmospheric Administration (NOAA).



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