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Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

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<strong>Transportation's</strong> <strong>Role</strong> <strong>in</strong> Reduc<strong>in</strong>g U.S. <strong>Greenhouse</strong> <strong>Gas</strong> <strong>Emissions</strong>: Volume 1<br />

Gulf Coast area found that 27 percent of major roads <strong>in</strong> the region are vulnerable<br />

to a four-foot sea level rise, and almost one-half the rail miles <strong>in</strong> the region could<br />

be impacted by an 18 foot storm surge. 23 Changes <strong>in</strong> the frequency and <strong>in</strong>tensity<br />

of extreme weather events can disrupt aviation operations. Increases <strong>in</strong> extreme<br />

temperature and precipitation events may also necessitate changes <strong>in</strong> structural<br />

design. In the Arctic where many transportation facilities are built on permafrost<br />

foundations, thaw<strong>in</strong>g permafrost is already damag<strong>in</strong>g roads and airports.<br />

Melt<strong>in</strong>g sea ice <strong>in</strong> Arctic summers may eventually open a Northwest Passage sea<br />

lane, chang<strong>in</strong>g sea shipp<strong>in</strong>g routes across the globe while dramatically alter<strong>in</strong>g<br />

Arctic ecological systems. 24<br />

This report to Congress focuses on mitigation strategies to reduce transportation<br />

GHGs. Other ongo<strong>in</strong>g DOT projects focus on measures to adapt transportation<br />

<strong>in</strong>frastructure to accommodate the effects of climate change, <strong>in</strong>clud<strong>in</strong>g a major<br />

study of the central Gulf Coast region.<br />

2.2 TRANSPORTATION GREENHOUSE GAS EMISSIONS<br />

GHGs are produced from multiple sectors of the economy, <strong>in</strong>clud<strong>in</strong>g <strong>in</strong>dustrial<br />

sources, electric power plants, residences, and agriculture; as well as the different<br />

transportation modes. Unlike criteria air pollutants, the ma<strong>in</strong> GHGs are global <strong>in</strong><br />

nature. They do not create toxic “hot spots,” but rather are well-mixed <strong>in</strong> the<br />

atmosphere <strong>in</strong> the long-run. Thus, the impacts of one ton of carbon dioxide<br />

emissions are the same no matter where it is emitted, or by what sector of the<br />

economy. In that sense, the relative effect of transportation emissions on the<br />

global climate can be approximated by their relative magnitude compared to all<br />

other global emissions.<br />

The primary GHGs produced by the transportation sector are carbon dioxide,<br />

methane, nitrous oxide, and hydrofluorocarbons (HFC). 25 Carbon dioxide, a<br />

product of fossil fuel combustion, accounts for 95 percent of transportation GHG<br />

23 U.S. Climate Change Science Program (CCSP) (2008). Impacts of Climate Change and<br />

Variability on Transportation Systems and Infrastructure: Gulf Coast Study, Phase I. A<br />

Report by the U.S. Climate Change Science Program and Subcommittee on Global<br />

Change Research [Savonis, M.J., V.R. Burkett, and J.R. Potter (eds.)]. United States<br />

Department of Transportation, Wash<strong>in</strong>gton, D.C..<br />

24 Transportation Research Board (TRB) (2008). Potential Impacts of Climate Change on U.S.<br />

Transportation. Transportation Research Board Special Report 290, Committee on<br />

Climate Change and U.S. Transportation, Transportation Research Board, Division on<br />

Earth and Life Sciences, National Research Council, Wash<strong>in</strong>gton, D.C.<br />

25 These gases do not have equal global warm<strong>in</strong>g potential (GWP), a measure of relative<br />

radiative forc<strong>in</strong>g compared to CO2. Therefore, unless otherwise noted, figures are<br />

presented <strong>in</strong> CO2 equivalents, or CO2e. That is, figures for non-CO2 GHGs are<br />

converted <strong>in</strong>to the amount of CO2 that would cause the same degree of warm<strong>in</strong>g.<br />

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