The worst potential scenario for sea level rise around the US coastline this century is more than two metres, says an authoritative report issued today by NOAA's Climate Program Office.
Regardless of how much warming occurs over the next 100 years, sea level rise is not expected to stop in 2100.
More than 8 million people in the US live in areas at risk of coastal flooding. Along the Atlantic Coast alone, almost 60 percent of the land that is within a metre of sea level is planned for further development, with inadequate information on the potential rates and amount of sea level rise.
The report Global Sea Level Rise Scenarios for the United States National Climate Assessment says global sea level rise has been a persistent trend for decades.
It concludes that it is expected to continue beyond the end of this century, which will cause significant impacts in the United States. Scientists have very high confidence (greater than 90% chance) that global mean sea level will rise at least 8 inches (0.2 meter) and no more than 6.6 feet (2.0 meters) by 2100.
Many of the nation's assets related to military readiness, energy, commerce, and ecosystems that support resource-dependent economies are already located at or near the ocean, thus exposing them to risks associated with sea level rise.
The report is published by NOAA's Climate Program Office in collaboration with twelve contributing authors from ten different federal and academic science institutions—including NOAA, NASA, the U.S. Geological Survey, the Scripps Institution of Oceanography, the U.S. Department of Defense, the U.S. Army Corps of Engineers, Columbia University, the University of Maryland, the University of Florida, and the South Florida Water Management District.
It was produced in response to a request from the U.S. National Climate Assessment Development and Advisory Committee and provides a synthesis of the scientific literature on global sea level rise, and a set of four scenarios of future global sea level rise. The report includes input from national experts in climate science, physical coastal processes, and coastal management.
The authors say they have tried to interpret the qualitative and quantitative information about different aspects of future environmental change to investigate the potential consequences for society.
Scenarios do not predict future changes, but describe future potential conditions in a manner that supports decision-making under conditions of uncertainty.
The report says: “We have very high confidence (greater than 9 in 10 chances) that global mean sea level (based on mean sea level in 1992) will rise at least 8 inches (0.2 meters) and no more than 6.6 feet (2 meters) by 2100. The biggest source of uncertainty within this range is the contribution of water from melting ice sheets and glaciers in Greenland and West Antarctica.
• The lowest sea level change scenario (8 inch rise) is based on historic rates of observed sea level change. This scenario should be considered where there is a high tolerance for risk (e.g. projects with a short lifespan or flexibility to adapt within the near-term)
• The intermediate-low scenario (1.6 feet) is based on projected ocean warming
• The intermediate-high scenario (3.9 feet) is based on projected ocean warming and recent ice sheet loss
• The highest sea level change scenario (6.6 foot rise) reflects ocean warming and the maximum plausible contribution of ice sheet loss and glacial melting. This highest scenario should be considered in situations where there is little tolerance for risk.
The authors say the actual amount of sea level change at any one region and location will vary greatly in response to regional and local vertical land movement and ocean dynamics.
Parts of the Gulf Coast and the Chesapeake Bay will continue to experience the most rapid and highest amounts of sea level rise, as the land in some of these areas is subsiding, and adding to the overall "net" sea level rise.
Parts of Alaska and the Pacific Northwest may experience much less sea level change or none at all, as the land in some of these areas is still rebounding from the last glaciation at a faster rate than sea level rise.
It is certain that higher mean sea levels increase the frequency, magnitude, and duration of flooding associated with a given storm. Flooding has disproportionately high impacts in most coastal regions, particularly in flat, low-lying areas.
The NOAA is the leading provider of weather, water, and climate information and services to the US and the world. Established in October 2005, NOAA's Climate Program Office (CPO) provides strategic guidance and oversight for the agency's climate science and services programs.