Changes in GHG Concentration
The concentration of GHGs is increasing in the atmosphere since the beginning of the Industrial era, mainly due to the increase in human activities. However, the extent to which each GHG perturbs the climate system over a particular time period depends on the concentration of the gas in the atmosphere over that period and its radiative forcing.
The largest contribution comes from the burning of fossil fuels, mainly for transportation, heating and cooling of buildings, and industrial applications. There has been a remarkable increase in the combined radiative forcing of CO2, CH4, and N2O over the last few centuries. The increase during the past four decades has been at least six times faster than that observed over the last two millennia (IPCC, 2007).
The following table depicts how human activities have multiplied the GHG pile up.
Source (Human Activities)
Atmospheric Residence Time
Fossil fuel burning, deforestation, land use
Industry and agriculture (fertilizers), fibre production, and fossil fuel burning
Agriculture, wetlands, biomass burning, industries, waste-dumped lands
* ppm â€“ parts per million
** ppb â€“ parts per billion
Other significant GHGs include CFCs (cholorofluorocarbons) and HCFCs (hydrochlorofluorocarbons). Industry is the main source of the emission of these gases. Emissions of some of these gases have been controlled, which are showing a decreasing trend. There are some other gases like HFCs (hydrofluorocarbons), PFCs (perfluorocarbons), and SF6 (sulphur hexafluoride), which are observed to be increasing in concentration.
Tropospheric ozone, a short-lived GHG, is produced by the chemical reactions of carbon monoxide, nitrogen oxides, and formaldehyde. Changes in ozone concentrations due to the increase in emissions or changes in climate are, however, not very well understood as of now. A strong correlation between ozone concentrations and air quality and temperature has been observed; for example, exceptionally high concentrations of ozone were observed in the troposphere during the summer heat wave in Europe in 2003.