Sea Level Rise
The Science and Climate Change Connection
Sea levels have risen by eight to ten inches since they began increasing in the middle of the 19th century. The rise has accelerated, with its rate doubling since 1992 (NCA). These changes stand in stark contrast to the prior 2,000 years, when there was little change (Titus et al. 2009). If emissions go unchecked, we are likely to see a meter of sea level rise by 2100, according to a survey of experts (Horton et al. 2014).
Sea level rise is already impacting coastal communities in the United States. These impacts are occurring through changes in storm surge, tidal flooding and saltwater intrusion into fresh water aquifers. Sea level rise will put more homes and infrastructure at risk from hurricanes, as much as a 230 percent increase in houses at risk by 2100 (Maloney and Preston 2014). During Hurricane Sandy, sea level rise enabled the storm surge to reach an additional 80,000 homes.
While sea level rise may be modest relative to the total height of storm surge or high tides, it can be the straw that breaks the camel’s back. Human infrastructure and natural systems have developed to cope with a range of historical extremes, such as 100-year events. New, more intense extremes can overwhelm and collapse existing human systems and structures, crossing thresholds that represent tipping points for greater damages (Peterson et al. 2008). Coastal infrastructure including roads, rail lines, energy infrastructure, and port facilities including naval bases, are at risk from storm surge that is exacerbated by rising sea levels (Steig 2009).
Higher sea levels also destroy the marshes and wetlands that provide coastal areas with an essential buffer from storms and flooding.
Climate change drives sea level rise in two major ways. First, warming expands the volume of water in the oceans, which pushes up sea levels. Second, warming also melts glaciers and ice sheets on land, with the run-off adding to sea levels. Melting sea ice is not a significant factor. For instance, consider how ice cubes melting in a glass of water don’t raise the water level.
Regional sea levels vary based on regional and local changes in land movement and long-term changes in coastal circulation patterns. Looking forward, the science consensus suggests an upper limit of 6.6 feet of global rise by 2100 should be used for risk analysis (NCA Chpt 2, p.63).