Increasing concentration of greenhouse gases in the atmosphere

The gases carbon dioxide COâ‚‚, methane CHâ‚„ and nitrous oxide Nâ‚‚O are among the principal causes of human-induced climate change. They are found in the atmosphere in the absence of human activity, but the increases in their concentrations are due to human activities such as burning fossil fuels, deforestation and agriculture (livestock, rice paddies, and the use of nitrogen-based fertilisers). They are all from biological or fossil fuel sources.

There are a number of other gases that are present in trace amounts in the atmosphere and which are known to aggravate the problems of global warming. Only a few are present in sufficient concentration and have sufficiently strong radiation absorption bands in the thermal radiation window that contains up to 30% of the upward infrared radiation from the Earth's surface. However practically all these gases are increasing in the troposphere and their total effect may be comparable to that of the major gases. They include other gaseous oxides of nitrogen, carbon monoxide, volatile organic compounds and tropospheric ozone and its precursors and synthetic greenhouse gases: chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), most perfluorocarbons (PFCs), sulfur hexafluoride (SF₆), and others. Several, most famously CFCs, also deplete the ozone layer and are regulated under the Montreal Protocol. Others, such as HFCs, were actually first produced in large quantities to replace the ozone-depleting substances, but unfortunately turned out to be potent greenhouse gases too.   Most of these gases are emitted exclusively by humans and have been used variously as aerosol spray propellants, refrigerants, fire-extinguishing agents, and in the production of semiconductors, among other industrial applications.  Dichlorodifluoromethane (CFC-12) and trichlorofluoromethane (CFC-11) are the third and fifth most important greenhouse gases respectively, in terms of their overall contributions to global warming.

the synthetic greenhouse gases chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), most perfluorocarbons (PFCs), sulfur hexafluoride (SF₆), and others. Several, most famously CFCs, also deplete the ozone layer and are regulated under the Montreal Protocol. Others, such as HFCs, were actually first produced in large quantities to replace the ozone-depleting substances, but unfortunately turned out to be potent greenhouse gases too.  Dichlorodifluoromethane (CFC-12) and trichlorofluoromethane (CFC-11) are the third and fifth most important greenhouse gases respectively in terms of their overall contributions to global warming.

The IPPC announced in 1992 that the global rates of emission of methane and CFCs were decreasing, that emissions of carbon dioxide had remained stable for 1990 and 1989, after a 5% increase over 1987, and other rates of emissions of greenhouse gases continued to grow. The US government prediction in 2002 was that that US production of greenhouse gases will rise 43 percent by 2020.

According to the European Environment Agency: The total concentration of all greenhouse gases, including cooling aerosols, reached a value of 449 ppm in CO2 equivalents in 2016 — an increase of more than 4 ppm compared with 2015, and 33 ppm more than 10 years ago.