Sea Level Rise

Sea levels are rising rapidly

Sea levels have risen between eight to ten inches since they began increasing in the middle of the 19th century. The speed of rising has accelerated, with its rate doubling since 1992. These changes stand in stark contrast to the prior 2,000 years, when there was very little change. If emissions go unchecked, we are likely to see one meter of sea level rise by 2100, which will have severe consequences for coastal cities, built infrastructure and human migration. One study shows that 13 million people may live in vulnerable regions along the U.S. coasts by 2100 if sea levels rise by 5.9 feet (1.8 m).

Water volumes are expanding, land ice and glaciers are melting

Climate change drives sea level rise in two major ways. First, the warming temperatures expands the volume of water in the oceans, which pushes up sea levels. Second, the warming also melts glaciers and ice sheets on land, which end up flowing off into the oceans, adding to sea levels. Melting sea ice is not a significant contributor to sea level rise. 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. However, the science consensus suggests an upper limit of 6.6 feet of global sea level rise by 2100.

Sea level rise is already making American lives more vulnerable

Study after study has shown that sea-level rise due to climate change will leave cities on the coasts of United States vulnerable to severe and more frequent flooding. Despite the warnings, Americans continue to live and build in regions likely to be inundated with water in a matter of decades. One study shows that 13 million people may live in vulnerable regions along the U.S. coasts by 2100 if sea levels rise by 5.9 feet (1.8 m).

Sea level rise is not a future effect of climate change- it is already impacting coastal communities in the United States today. Changes in storm surge, tidal flooding and saltwater intrusion into freshwater aquifers damage infrastructure, threaten homes, postpone or damage economic activity and increase human migration. Higher sea levels also destroy marshes and wetlands that provide coastal areas with an essential buffer from storms and flooding. 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. During Hurricane Sandy for example, 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. 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.

For more information on sea level rise, including the state of scientific understanding, relevant news and specific impacts, visit Climate Signals.

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