WMO reports GHG reached new high in 2010 since pre-industrial times; special attention on rising N2O concentrations
The amount of greenhouse gases in the atmosphere reached a new high in 2010 since pre-industrial time and the rate of increase has accelerated, according to the World Meteorological Organization’s (WMO) Greenhouse Gas Bulletin. The Bulletin focused special attention on rising nitrous oxide (N2O) concentrations.
Between 1990 and 2010, according to the report, there was a 29% increase in radiative forcing—the warming effect on our climate system—from greenhouse gases. Carbon dioxide accounted for 80% of this increase.
After water vapor, the three most prevalent long-lived greenhouse gases are carbon dioxide, methane and nitrous oxide.
Carbon dioxide is the single most important man-made greenhouse gas in the atmosphere and contributes about 64% to total increase in climate forcing by greenhouse gases. Since the start of the industrial era in 1750, its atmospheric abundance has increased by 39% to 389 parts per million. This is primarily because of emissions from combustion of fossil fuels, deforestation and changes in land-use.
Between 2009 and 2010, its atmospheric abundance increased by 2.3 parts per million—higher than the average for both the 1990s (1.5 parts per million) and the past decade (2.0 parts per million).
For about 10,000 years before the start of the industrial era in the mid-18th century, atmospheric carbon dioxide remained almost constant at around 280 parts per million.
Methane (CH4) contributes about 18% to the overall global increase in radiative forcing since 1750 and is the second most important greenhouse gas after carbon dioxide.
Before the start of the industrial era, atmospheric methane was about 700 parts per billion (number of molecules of the gas per billion molecules of dry air) Since 1750, it has increased 158%, mostly because of activities such as cattle-rearing, rice planting, fossil fuel exploitation and landfills. Human activities now account for 60% of methane emissions, with the remaining 40% being from natural sources such as wetlands.
After a period of temporary relative stabilization from 1999 to 2006, atmospheric methane has again risen. Scientists are conducting research into the reasons for this, including the potential role of the thawing of the methane-rich Northern permafrost and increased emissions from tropical wetlands.
Nitrous oxide contributes about 6% to the overall global increase in radiative forcing since 1750. It is emitted into the atmosphere from natural and man-made sources, including the oceans, biomass burning, fertilizer use and various industrial processes. It is now the third most important greenhouse gas.
The atmospheric burden of nitrous oxide in 2010 was 323.2 parts per billion—20% higher than in the pre-industrial era. It has grown at an average of about 0.75 parts per billion over the past ten years, mainly as a result of the use of nitrogen containing fertilizers, including manure, which has profoundly affected the global nitrogen cycle.
Its impact on climate, over a 100-year period, is 298 times greater than equal emissions of carbon dioxide. It also plays an important role in the destruction of the stratospheric ozone layer.
Other greenhouse gases. The combined radiative forcing by halocarbons is 12%. Some halocarbons such as chlorofluorocarbons (CFCs), previously used as refrigerants, as propellants in spray cans and as solvents, are decreasing slowly as a result of international action to preserve the Earth’s protective ozone layer.
However, concentrations of other gases such as HCFCs and HFCs, which are used to substitute 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 carbon dioxide. (Earlier post.)