previous work on strategies for reducing transportation-related emissions of carbon dioxide (CO2)—the primary GHG—that contribute to climate change, a relatively well-researched area (see Appendix B).

Climate change will have significant impacts on transportation, affecting the way U.S. transportation professionals plan, design, construct, operate, and maintain infrastructure. Decisions taken today, particularly those related to the redesign and retrofitting of existing or the location and design of new transportation infrastructure, will affect how well the system adapts to climate change far into the future. Focusing on the problem now should help avoid costly future investments and disruptions to operations. The primary objective of this report is to provide guidance for transportation decision makers on how best to proceed.

CLIMATE CHANGES OF GREATEST RELEVANCE FOR U.S. TRANSPORTATION

Climate change is not just a problem for the future. Recent global climate changes, such as warming temperatures and rising sea levels, likely reflect the effects of GHG emissions into the atmosphere over the past century. Even if drastic measures were taken today to stabilize or eliminate GHG emissions, the effects of climate change would continue to be experienced, and U.S. transportation professionals would have to adapt to their consequences.

On the basis of current knowledge, climate scientists have identified five climate changes of particular importance to transportation and estimated the probability of their occurrence during the 21st century (detailed in Box S-1):

  • Increases in very hot days and heat waves,

  • Increases in Arctic temperatures,

  • Rising sea levels,

  • Increases in intense precipitation events, and

  • Increases in hurricane intensity.

Climate scientists have the greatest confidence in projected changes in mean temperature and other climate factors at the global or continental scale; confidence in these projections diminishes as the geographic scale is



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