Burning Fossil Fuels: burning coal to generate electricity, burning oil to power vehicles and aircraft (vehicle emissions), or burning wood in fires used for cooking or to provide heat, etc. changes the state of stored organic carbon from a liquid (e.g. oil) or solid (e.g. coal/wood) into a gas (carbon dioxide) which is released into the atmosphere.
Deforestation: vegetation absorbs carbon dioxide from the atmosphere during the process of photosynthesis, converting this to carbon which is stored within all plants (i.e it is a carbon sink). When vegetation is burned, this organic carbon is released into the atmosphere in the form of carbon dioxide, and in so doing becomes a carbon source rather than a carbon sink.
Decomposing organic matter: landfills, animal waste, sewerage and dams are all human sources of methane. For example, organic matter is trapped behind dam walls where it sinks to the bottom of the dam and decomposes. Bacteria produce methane in the decomposition process, which slowly escapes to the surface and is released into the atmosphere. Landfill gas operations and biodigesters provide a method of mitigation, and not only harness methane that would otherwise be released into the atmosphere, but also provide an alternative source of fuel.
Natural gas extraction: methane escapes during oil and gas extraction (e.g. fracking) operations and is released into the atmosphere.
Nitrous oxide is a potent greenhouse gas that is released primarily by fertilizers used in agriculture and landscaping, but also during the burning of fossil fuels and other organic matter. Atmospheric nitrous oxide levels have risen by roughly 18% since the Industrial Revolution, spiking rapidly towards the end of the 1900’s.
Water Vapor
Water is essential for life, and as it is constantly cycling from one state to another, it is not surprising that it is the most abundant of all the greenhouse gases. However, water vapor not only acts as a greenhouse gas, it also increases as the atmosphere gets warmer and provides climate feedbacks. While humans do not play a large direct role in producing water vapor, other human emissions promote atmospheric warming, which in turn promote evaporation that results in more water vapor in the atmosphere.
Chlorofluorocarbons
Chlorofluorocarbons (CFCs) are long-lasting greenhouse gases that also destroy the ozone layer. CFCs do not occur naturally in the atmosphere – they are synthetic compounds that only originate from human sources, including: aerosols, foaming agents, refrigerants, and other industrial applications.