Global Warming

The term global warming refers to a warming in the earth's climate. Global temperatures have changed throughout earth's history; however, in common usage, the term global warming refers to the anthropogenic (human induced) warming that results from an increase in atmospheric concentrations of certain gases due to the burning fossil fuels since the Industrial Revolution. This phenomenon is also called the greenhouse effect, and is a specific case of the more general term global climate change (which also refers to climate cooling both human induced and otherwise). Average global temperature has risen 0.6 ± 0.2 degrees C over the 20th century. The Intergovernmental Panel on Climate Change (IPCC) reports that most of the warming observed over the past 50 years is attributable to human activities. IPCC also reports that the 1990s were the warmest decades and 1998 was the warmest year since 1861.

How does this happen? The earth surface absorbs energy from the sun and radiates it back into the atmosphere. An increase in “greenhouse gases,” including carbon dioxide (CO2), methane (CH4), ozone (O3), chlorofluorocarbons (CFC's), Nitrous oxides (N20) and sulfur hexaflouride (SF6) form a [Page 791]layer of insulation that traps the earth's outgoing heat, much as air is trapped inside a greenhouse. The increased concentration of these gases traps more heat and causes the earth's overall temperature to become warmer.

The atmospheric concentration of greenhouse gases has increased over the last century due to industrial and agricultural activity. The most significant greenhouse gas by volume is carbon dioxide. Carbon dioxide is released into the atmosphere through the burning of fossil fuels (oil, natural gas, and coal) in vehicle exhaust, coal-fired power plants and industrial processes. Since the late 1950s, measurements made at the Mauna Loa Observatory in Hawaii record an increase in carbon dioxide concentrations within the atmosphere. Data from Mauna Loa and other sources indicate that atmospheric carbon dioxide concentrations in the atmosphere are now the highest in 150,000 years. Similarly, methane concentrations have increased as a result of the production and transportation of fossil fuels, rice paddy farming, livestock production, changes in land use from wetlands, and emissions from municipal solid waste landfills as organic waste decomposes. Nitrous oxide is released from agricultural and industrial activities, and the combustion of both and fossil fuels and solid waste. Hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6), are greenhouse gases that are not naturally occurring, which are generated in a variety of industrial processes.