What are Greenhouse Gases?

Greenhouse gases are gases in the earth's atmosphere that trap energy from the sun and keep it within our atmosphere.

The term greenhouse gas effect is used to describe the natural process of heat trapped in the earth's atmosphere by various gases called greenhouse gases (GHG). The major greenhouse gases are naturally occurring and include water vapor, ozone, carbon dioxide (CO2), methane (CH4 ), and nitrous oxide (N2O).

Each gas has its own potency in terms of greenhouse warming potential. For example, methane is 21 times more potent than carbon dioxide, and nitrous oxide is 310 times more potent than carbon dioxide. Therefore, gas concentrations are often given in carbon dioxide equivalents.

Natural emissions are the most abundant emissions and ultimately good. Without them, the earth's average temperature would be about 33C lower than it is, which would be about -15C, making our planet uninhabitable.

While the earth's atmosphere still contains what we consider natural or 'good' greenhouse gases, it is also experiencing an increased build up of human-produced gases. Even though these human produced gases or anthropogenic gases are not as great as the naturally occurring ones, the majority in the scientific community believe that they are creating climate change.

Most human-induced emissions are in the form of carbon dioxide from burning fossil fuels from such sources as transportation, manufacturing and heating and in the form of halocarbons (CFCs) from sources such as refrigerants.

During the last decade, global warming and climate variability have become major policy issues worldwide. In the United States, the transportation sector alone is currently responsible for approximately 28 percent of all man- made GHG emissions. This percentage is forecast to remain high given the continued demand for gasoline, diesel fuel, and jet fuel.

According to EPA, it is estimated that approximately 33 percent of GHG emissions in the United States come from transportation, and 72 percent of the transportation sector’s emissions are generated by road use. Because of the amount of GHG from motor vehicles, as noted earlier, there is a lot of interest in policies to reduce the growth of highway demand by shifting trips to other modes of travel. AASHTO, for example, supports a policy to double transit ridership by 2030. There is hope that making more trips by biking, walking, and there is hope that the growing trend in telecommuting will reduce GHG emissions as well. Because of the significance of GHG emissions from transportation sources, in 2008, representatives from several Federal agencies met to discuss overall opportunities to reduce these emissions through the coordination of Federal programs that influence land-use decisions to decrease the growth in VMT.  The agencies formed an interagency working group with the mission of aligning Federal programs and resources to support achieving GHG reductions though transportation decision-making and land-use. The working group has continued to meet monthly since its inception to identify interagency activities that will support its mission and ultimately result in reduced growth in VMT of cars and trucks. Additionally, with a new Administration in the White House and with transportation reauthorization discussions underway, the FHWA is focusing new attention on coordinating its policies, programs, and funding related to transportation, land use, and climate change to meet the agency's goal of reducing GHG emissions and growth in VMT.

The MPO is currently addressing climate change in the MTP planning process from both mitigation and an adaptation perspective. The FHWA states that “broad geographic scope and time scale of the planning process makes it an appropriate place to consider GHG emissions and the effects of climate change.”

Tracking greenhouse gases

The US EPA tracks greenhouse gases. Greenhouse gas inventories are an accounting of the amount of greenhouse gases emitted to or removed from the atmosphere over a specific period of time and may also provide information on the activities that cause emissions and removals, as well as background on the methods used to make the calculations. Policy makers use greenhouse gas inventories to track emission trends, develop strategies and policies and assess progress. Scientists use greenhouse gas inventories as inputs to atmospheric and economic models.

To track the national trend in emissions and removals since 1990, EPA develops the official U.S. greenhouse gas inventory each year. The national greenhouse gas inventory is submitted to the United Nations in accordance with the Framework Convention on Climate Change.

Sources:

http://greenliving.about.com/od/planetissues/a/GHGSource.htm

http://www.epa.gov/climatechange/emissions/index.html

http://www.epa.gov/climatechange/emissions/usinventoryreport.html

http://www.unep.org/ozone/pdf/Montreal-Protocol2000.pdf