Greenhouse Gas Emissions

Greenhouse gases trap heat in the Earth’s atmosphere affecting climate change. Some greenhouse gases such as carbon dioxide and water vapor occur naturally and are emitted to the atmosphere through natural processes and human activities. Other greenhouse gases are emitted mostly through human activities. The principal greenhouse gases caused by human activities are:

Carbon Dioxide (CO2): Carbon dioxide enters the atmosphere through the burning of fossil fuels (oil, natural gas, and coal), solid waste, trees and wood products, and also as a result of chemical reactions. Carbon dioxide is also removed from the atmosphere (or “sequestered”) when it is absorbed by plants as part of the biological carbon cycle.

Methane (CH4): Methane is emitted during the production and transportation of fossil fuels such as coal, natural gas, and oil. Methane emissions also result from raising livestock and agricultural practices, the decay of organic waste in solid waste landfills, and small amounts during the combustion of fossil fuels in transportation.

Nitrous Oxide (N2O): Nitrous oxide is emitted during agricultural and industrial activities, as well as small amounts during combustion of fossil fuels and solid waste.

Ozone Depleting Substances and Fluorinated Gases: Certain Ozone Depleting Substances (CFC-11, CFC-12, CFC-113, CFC-114, CFC-115, HCFC-22, and HCFC-141b) regulated under the Montreal Protocol are also considered grenhouse gases (GHG). In December 2010, California Air Resources Board included ODS projects as an approved carbon offset for California’s forthcoming GHG cap-and-trade program.   Fluorinated gases are sometimes used as substitutes for ozone-depleting substances. These gases are typically emitted in smaller quantities, but are potent greenhouse gases based on their global warming potentials. Hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride are synthetic, greenhouse gases that are emitted from a variety of industrial processes.