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Climate Change


Delaware and sea level rise

Causes of sea level rise

There is no doubt that sea level is rising both worldwide and along parts of Delaware's coastline. The majority of sea level rise comes from thermal expansion of the ocean’s waters —an effect of global warming. The melting of glaciers and ice caps also contributes a significant amount to sea level rise, with somewhat smaller contributions coming from the melting of the Greenland and Antarctic Ice Sheet.

 In Delaware, there also is an effect from local land “subsidence.” Here, sea level rises relative to the land, as the land slowly drops due to the after-effects of the last Ice Age. While thermal expansion is currently the main contributor to global sea level rise, contributions from the melting of glaciers and ice sheets will eventually become the dominant factor as temperatures continue to rise.

Historical and Current Sea Level Rise

Scientific measurements and data indicate that the total 20th-century global sea level rise was about 17 mm, or 6.7 inches.

Photo by Elena Tkacz

Based on tide gauge data, sea level has risen about 13 inches in the last 100 years in Delaware. Delaware’s coastline, including the many miles of beaches, inland waterways, and associated wetlands and wildlife, as well as commercial and residential property, could be negatively impacted by continued sea level rise.

Between 1961 and 2003, global sea level rose at an average rate of 1.8 mm per year. At the later part of the century, between 1993 and 2003, the rate was much higher—about 3.1 mm per year (see the IPCC’s most recent report on climate change for further details).

The sea level in Delaware is rising as well. Research has shown that the sea level in Delaware has been rising for the last 12,000 to 14,000 years, or since the last ice age. Sediment analysis along the Delaware coastline indicates that sea level rise in Delaware has averaged about 0.9 mm per year over the past 1200 years, while tide gauge data shows a rise of about 3.3 mm per year over the past 100 years (see Nikitina et al., 2000; USEPA, 1997). Moreover, the most recent estimates from the U.S. EPA indicate that sea level has been rising 0.08-0.12 inches per year (2.0-3.0 mm per year) along most of the U.S. Atlantic and Gulf coasts. Based on past and current estimates, scientists are now concerned that the rate of sea level rise may be accelerated in the future.

Impact of Sea Level Rise on Delaware

The Sea Level Rise Advisory Committee has published Preparing for Tomorrow’s High Tide: Sea Level Rise Vulnerability Assessment for the State of Delaware. It contains background information about sea level rise, methods used to determine vulnerability and a comprehensive accounting of the extent and impacts that sea level rise will have on 79 resources in the state. The information contained within this document and its appendixes will be used by the Delaware Sea Level Rise Advisory Committee and other stakeholders to guide development of sea level rise adaptation strategies. 

Future Sea Level Rise

The Intergovernmental Panel on Climate Change (IPCC) has projected global average sea level rise estimates for the end of the 21st century based on a number of different emission scenarios. Under the low green house gas emission scenario, sea level is expected to rise between 7 and 15 inches by 2100; under the high emission scenario, sea level is expected to rise between 10 and 23 inches by 2100.

These estimates mean that continued sea level rise in Delaware could be a concern, although there is considerable uncertainty and disagreement among researchers regarding the rate of future sea level rise in Delaware.  Also, according to the IPCC, current model projections indicate substantial variability in future sea level rise between different locations. This means that some locations could experience sea-level rise higher than the global average projection, while others could actually have a fall in sea level. However, using the historical data for Delaware mentioned above, and given the fact that overall global temperatures and sea level are predicted to continue to rise worldwide, it is likely that sea level in Delaware will continue to rise at a rate at least equal to that already seen—about 3 mm per year, or 12 to 13 inches total over the next 100 years.

The consequences of continued sea level rise in Delaware—such as coastal flooding, storm surge damage, and wetlands loss—are reasonably well understood by observing the effects of past rise. These are addressed in subsequent sections.

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