GHG concentrations continue climbing

In 2010, levels of greenhouse gases in the atmosphere reached a new high since pre-industrial time and the rate of increase has accelerated, according to the World Meteorological Organization (WMO).

Between 1990 and 2010, there was a 29 per cent increase in radiative forcing – the warming effect on our climate system – from greenhouse gases (GHG), with carbon dioxide (CO2) accounting for 80 per cent of this increase.

CO2 is the single most important man-made GHG and contributes about 64 per cent to the total increase in climate forcing. Since the start of the industrial era in 1750, its atmospheric abundance has increased by 39 per cent to 389 parts per million (ppm), primarily because of emissions from combustion of fossil fuels, deforestation and changes in land use.

Between 2009 and 2010, CO2 concentrations increased by 2.3 ppm – higher than the average for both the 1990s and the past decade.

Methane (CH4) has contributed about 18 per cent to the increase in radiative forcing since 1750 and is the second most important GHG. Since 1750, it has increased by 158 per cent, mostly because of activities such as cattle-rearing, rice planting, fossil fuel exploitation and landfills.

Nitrous oxide (N2O) has contributed about six per cent to the increase in radiative forcing since 1750, and is the third most important GHG. The atmospheric burden of N2O is now 20 per cent higher than in the pre-industrial era, mainly as a result of the use of nitrogen-based fertilisers, including manure, which has profoundly affected the global nitrogen cycle.

The combined radiative forcing by halocarbons is 12 per cent. Some halocarbons such as chlorofluorocarbons (CFCs) are decreasing slowly as a result of international action to preserve the Earth's protective ozone layer. However, concentrations of other GHGs such as HCFCs and HFCs, which are used as substitutes for CFCs because they are less damaging to the ozone layer, are increasing rapidly. These two classes of compounds are very potent greenhouse gases and last much longer in the atmosphere than CO2.

Source: WMO, 21 November 2011 Web link: http://www.wmo.int/pages/mediacentre/press_releases/pr_934_en.html

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