The natural presence of greenhouse gases in the atmosphere is necessary to sustain life on Earth. Without these gases, the temperature would be much too low for life as we know it to exist. The phenomenon of heat retention, or the “greenhouse” effect, occurs because greenhouse gas molecules allow energy from the sun to enter the atmosphere but prevent that energy from leaving.

With the beginning of the industrial revolution in approximately 1750, humans began to alter the balance of the atmosphere by producing greenhouse gases such as carbon dioxide, methane, and nitrous oxide. The increase in carbon dioxide is primarily caused by the combustion of fossil fuels (oil and gas) and deforestation. Livestock, the decomposition of organic waste, and production and transportation of oil, coal, and natural gas create methane emissions. Nitrous oxide is produced from industrial and agricultural processes and the burning of fossil fuels. These gases are naturally found in the atmosphere along with other greenhouse gases such as water vapor and ozone. People also produce gases such as hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs), however, that do not occur in nature.

The amount of time both natural and human produced greenhouse gases remain in the atmosphere varies from a few years to over 100 years. When evaluating the effect of a specific gas, the ability to absorb IR (or terrestrial) radiation and be transmissive to solar radiation must be considered along with the atmospheric residence time. This is referred to as global warming potential. The global warming potential of some HFC compounds is more than 1000 times that of carbon dioxide.

It has been estimated that the Earth’s average surface temperature has risen approximately 0.5 to 1 degree Fahrenheit in the past 100 years and many scientists expect this trend to continue. This increase in temperature is often attributed to the increased levels of greenhouse gases in the troposphere (lower atmosphere) which in turn increases the amount of heat retained from the sun. The Earth’s natural temperature fluctuations make it difficult to quantify the actual effects of the rising concentrations of greenhouse gases. Most people can agree, however, that this pollution will have adverse effects.

If global temperatures are indeed rising, changes in climate can be expected. It is currently difficult to predict these climatic changes but precipitation patterns will likely alter making some areas more arid while others become wetter. Sea level is currently rising, and this trend will also continue. Changes like these will affect agriculture, wild life, and possibly human health.

URLs: Global Warming

http://yosemite.epa.gov/oar/globalwarming.nsf/content/Climate.html

http://www.nzherald.co.nz/storydisplay.cfm?storyID=3563965&thesection=news&thesubsection=general

http://www.ncdc.noaa.gov/oa/climate/globalwarming.html#Q1

http://yosemite.epa.gov/oar/globalwarming.nsf/UniqueKeyLookup/SHSU5BUM9T/$File/ghg_gwp.pdf

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