The latest report from the U.S. Geological Survey paints a cautionary tale for the East Coast. According to the report, rates of sea level rise are augmenting three-to-four times faster along the East Coast than they are globally. Increasing rates of sea level rise on the East Coast could spell disaster for major cities along the Atlantic coast, including cities such New York and Boston, the report warns.
The report says that sea-level rise from Cape Hatteras, North Carolina to Boston, Massachusetts (a 600-mile expanse of coastal zone called the “hotspot” by scientists) has grown 2-3.7 millimeters per year since 1990. For comparison, scientists say that the global growth rate over the same time frame was 0.6 -1.0 millimeter per year.
The report warns that if global temperatures continue to increase, rates of sea level rise along the East Coast are likely to continue growing. Scientists say this prediction is based on data and analyses that are detailed in the report.
The report demonstrates that the sea-level rise hotspot on the East Coast is in accordance with the retarding of Atlantic Ocean circulation. Several models suggest that this change in circulation may be connected to adjustments in water temperature, salinity and density in the subpolar north Atlantic.
“Many people mistakenly think that the rate of sea level rise is the same everywhere as glaciers and ice caps melt, increasing the volume of ocean water, but other effects can be as large or larger than the so-called ‘eustatic’ rise,” said USGS Director Marcia McNutt in a press release. “As demonstrated in this study, regional oceanographic contributions must be taken into account in planning for what happens to coastal property.”
Scientists say that global sea level will not increase at the same rate at every location, even though calculations show that it is likely to rise approximately two-to-three feet or more by the end of the 21st century. Sea level rise can vary both regionally and locally due to deviations in land movements, strength of ocean currents, water temperatures and other factors.
“Cities in the hotspot, like Norfolk, New York, and Boston already experience damaging floods during relatively low intensity storms,” said Asbury Sallenger, USGS oceanographer and project lead, in a statement. “Ongoing accelerated sea level rise in the hotspot will make coastal cities and surrounding areas increasingly vulnerable to flooding by adding to the height that storm surge and breaking waves reach on the coast.”
During the rest of this century, the surges in sea level rise rate that have already occurred in the 600-mile stretch on the East Coast will generate increases in sea level of 8 to 11.4 inches by 2100. This sea level growth would be in addition to global sea level rise.
USGS scientists looked at tide gauge data throughout much of North America in a way that removed long-term trends associated with vertical land movements. This allowed them to focus on recent changes in rates of sea-level rise caused by changes in ocean circulation.
The USGS report arrives on the heels of a similar report on the rate of sea level rise off most of California. The National Research Council (NRC) report said that the sea level off most of California is likely to rise about 36 inches over the next 100 years. The report also said that the sea levels off of the coasts of Washington, Oregon and northern California are expected to rise approximately 24 inches over the same time period.
“Global sea level has been rising due to both the warming of the oceans, which causes sea water to expand, and the melting of ice sheets and glaciers,” said Gary Griggs, a professor of Earth sciences and a member of the NRC committee, in a statement. “We know from tide gages that sea level rose globally about 7 inches over the past century. From satellite measurements over the past 20 years, however, we know that this rate has now nearly doubled, and we believe that this acceleration will continue well into the future.”
Like the USGS scientists, the NRC committee says that sea-level rise is uneven and will vary from place to place. The NRC report also says that tectonic plate movements are an important factor when it comes to sea-level rise because the movements cause the land to rise or sink in different locations.
The report comes as the world assembled for the Rio+20 UN sustainable development conference at the end of last week. The conference, which many considered a failure, was the latest attempt to curtail emissions from the U.S. and emerging economies. Leaders attending the conference failed to reach a compromise, the latest international meeting to break down without a consensus. A number of leading critics said key leaders shared the blame, including those who did not attend the conference. Among that list includes President Barack Obama of the U.S., Stephen Harper of Canada, Angela Merkel of Germany and David Cameron of the U.K.
Just as the USGS scientists expect increasing rates of sea level-rise to negatively impact the East Coast, the NRC report predicts a disturbing future for regions of the West Coast.
The NRC discovered through a simulation that sea-level rise could cause the occurrence of extreme water heights in the San Francisco Bay area to increase from about 9 hours per decade to several thousand hours per decade by the end of this century.
The NRC and USGS reports are growing evidence that global temperature increases will have major consequences for coastal cities.
The USGS is a science organization that disseminates information on our ecosystems, environments, natural hazards, natural resources and the consequences of climate and land-use change. The USGS report was recently published in the journal Nature Climate Change.