With a political and cultural debate about the impact of human activity on climate change, there are some differences in the greenhouse gases given as examples by different sources. For example, some sources ignore the contribution of water vapour and ozone to the greenhouse effect, while others claim that water vapour is by far the most significant greenhouse gas. With those differences in mind a politically neutral list of greenhouse gases includes carbon dioxide, methane, water vapour, ozone, fluorocarbons and nitrous oxide.
According to Nick Hopwood and Jordan Cohen of the University of Michigan, carbon dioxide (CO2) is our most prominent greenhouse gas. All animals inhale oxygen and exhale CO2, while plants take in CO2 and give off oxygen, so an increase in CO2 is to be expected as areas of the planet are cleared of forests and plants. In addition when we burn fossil fuels such as oil, coal or natural gas, their oxidation produces CO2. CO2 is also added to the atmosphere by the decay of plant and animal matter, forest fires, volcanic eruptions and the evaporation of seawater.
Whether its source is man-made or natural, according to a 1998 article by Gary W. Harding of Clemson University the atmospheric concentration of CO2 in Earth's atmosphere has increased by 80 parts per million (ppm) over the last two centuries.
Methane (CH4) is also called swamp gas because one of its sources is decaying organic matter without exposure to air, a normal situation in swamps and marshes. Many animals also produce significant amounts of methane naturally, including cattle, bison, buffalo and even termites. According to Hopwood and Cohen, human activity accounts for increased methane production through livestock production, sanitary landfills, coal mining, oil and natural gas production and agriculture.
Hopwood and Cohen caution that methane concentrations have doubled since 1750 and could increase by another 100 per cent by 2050. The U.S. Environmental Protection Agency estimates that more than half the methane produced is due to human activity.
Water Vapor and Ozone
According to Esperenet, an international environmental website, approximately 60 per cent of the greenhouse effect is attributable to water vapour, 20 per cent to CO2 and the rest due to methane, ozone, nitrous oxide and fluorocarbons. This group takes the view that human activity contributes only a small percentage of greenhouse gases.
Greenhouse gases online (GHGOnline) points out that ozone (O3) is an important greenhouse gas as well as an important factor in the formation and longevity of other greenhouse gases. They add that human activity has contributed to large increases in ozone in the last century.
Fluorocarbons are compounds of fluorine and carbon. They are commonly used as refrigerants in mechanical refrigeration devices such as air conditioners and refrigerators. Chlorofluorocarbons (CFCs) were the refrigerants of choice until it was discovered in the 1970s that they damaged the ozone layer. They have been replaced with hydrofluorocarbons which do not harm the ozone, but which are greenhouse gases. The Intergovernmental Panel on Climate Change (IPCC) stated in a report that there was a significant reduction of all fluorocarbons in the atmosphere between 1990 and 2000.
Nitrous oxide is a greenhouse gas familiarly known as laughing gas when used as an anesthetic. It is produced naturally by the oceans and bacteria in the soils. Hopwood and Cohen state that a significant increase in concentration is due in large part to the used of fertilisers, waste treatment and auto exhaust. Its concentration has increased by 15 per cent since 1750.