According to National Oceanic and Atmospheric Administration (NOAA), the global sea level has been rising over the past century, approximately 2.6 inches above the 1993 average and it continues to increase at a rate of about one-eight of an inch per year. According to the Intergovernmental Panel on Climate Change, since the peak of the last ice age, average global sea-levels have risen by more than 120 meters. Climate change is on track to raise sea level by one to three feet by the end of century (2100) even with the most aggressive emission cutes, due to the Greenhouse Gases already emitted. Although the impacts of sea level rise vary from place to place due to differences in the land elevation and SLR rate, but in general, the physical, economic and social consequences are massive; hence it is widely viewed as a threat to national security.

Sea level has been rising since the late 19th century or early 20th century when global temperatures began to increase, and NOAA researchers announce that it will continuously rise even at a higher rate during the 21st century (Lindsey, 2018). The IPCC (2007) estimated that global sea level rose an average of 1.7 ± 0.5 mm per year over the 20th century. Global sea-level rise (SLR) is caused by warmer climate which melts glaciers, ice caps, and ice sheets that accounts for about 40 percent of the observed SLR for 1961-2003 (National Research Council (NRC), 2012). How much and how fast it will rise depends on future global warming and the rate of glacier melting. Rising seas increase the risk of coastal flooding, storm surge, and coastal erosion (NRC, 2012). In 2017, global mean sea level was 3 inches above the 1993 average (Lindsey, 2018). NOAA scientists believe that global mean sea level will rise at least 8 inches by 2100 (Parris, 2012). 

Sea level rise, as one of the most wide-spread and important climate change factors, has become a pressing threat to transportation infrastructure, especially in coastal region. At the global level, flight cancels and travel delay are the major impact of flood and king tides on the transportation system.