CarbonTracker.com - Greenhouse gases and their sources

When people speak of greenhouse gases, they are generally referring to carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), sulfur hexafluoride (SF6), fluorinated gases (HFCs, PFCs, HCs, SF6) and water vapor (H2O).

Greenhouse gases (GHGs) contribute to global warming by trapping energy from the sun in the Earth’s atmosphere. This trapping of energy has a warming effect, hence the term “greenhouse” gases.

Greenhouse gases have both natural and human sources. Volcano eruptions, for example, are a source of atmospheric carbon dioxide. Nevertheless, human activities have become a major source of greenhouse gases, due in large part to the burning of fossil fuels and industrial processes. Not surprisingly, since the advent of the industrial revolution and the widespread adoption of fossil fuels as an energy source, the amount of greenhouse gases added to atmosphere each year has increased greatly. In 2005, for example, global atmospheric concentrations of CO2 were 30% higher than they were prior to the Industrial Revolution.

There is widespread scientific consensus that human activities are rapidly increasing the levels of greenhouse gases in the atmosphere. Although there is some natural variability in the amount of greenhouse gases in the atmosphere, geological records indicate that historical changes in atmospheric levels of greenhouse gases have occurred gradually over very long periods of time.

Greenhouse gases in detail

Carbon dioxide (CO2) is created by the burning of fossil fuels (oil, natural gas and coal), other organic solids, and also as a result of some chemical reactions (e.g., the manufacture of cement). Carbon dioxide is also removed from the atmosphere (or “sequestered”) when it is absorbed by plants. Learn more about carbon dioxide by clicking here.

Methane (CH4) is emitted during the production and transport of fossil fuels. Other major sources of methane emissions include livestock and other agricultural practices and the decay of organic waste in landfills. Methane has a global warming potential of approximately 21. In other words, methane is 21 times as powerful a greenhouse gas as carbon dioxide. Learn more about methane by clicking here.

Nitrous oxide (N2O) is emitted during agricultural and industrial activities, as well as by the burning of fossil fuels. Nitrous oxide has a global warming potential of 310, or is 310 times as powerful a greenhouse gas as carbon dioxide. Learn more about nitrous oxide by clicking here.

Fluorinated gases, such as Hydrofluorocarbons (HFCs), halocarbons (HCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF6), are emitted from a variety of industrial processes. These gases do not occur naturally in nature, but are rather wholly the result of human activities. Because they are very powerful greenhouse gases, they are sometimes referred to as High Global Warming Potential gases (“High GWP gases”). For example, sulfur hexafluoride has a global warming potential of approximately 23,900. In other words, SF6 is almost 24,000 times as powerful a greenhouse gas as carbon dioxide. To learn more about fluorinated gases click here.

Water Vapor (H2O) is a primary gas with a powerful greenhouse effect. Because the amount of water vapor in the air tends to rise as air temperatures increase, rising temperatures may result in a “positive feedback loop” (i.e. a cycle that reinforces itself) causing additional warming. To learn more about water vapor click here.

Next: Carbon Dioxide