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2 ,,,,.;' Sea Level Rising seas are perhaps one of the most immedi- ate, and possibly devastating, impacts of climate change in coastal areas. The potential consequences of sea level rise include submerged wetlands, eroded beaches, flooded coastal areas, increased salinity in freshwater aquifers and estuaries, and damage to both human property and coastal ecosystems. Using tide gauge records from around the world, scientists have been able to reconstruct global sea levels since 1700 and then analyze shifts in levels and associated rates of change (e.g., Jevrejeva et al. 2008). Although there are some differences in the estimates of the magnitude and rates of change based on underly- ing model assumptions and available data, the IPCC suggests that current sea level rise (SLR) has occurred at a mean rate of 1.8 mm per year for the past centu- ry (Bindoff et al. 2007). Recent satellite altimetry measurements suggest that this rate may be increas- ing, with a mean rate of 2.8 to 3.1 mm per year from 1993 — 2003 (Bindoff et al. 2007). Warming temperatures contribute to global sea level rise (SLR) through two mechanisms as tempera- ture rises: (1) ocean water expands and increases in volume and (2) land reservoirs of ice (in glaciers and ice flows) melt and contribute additional water to the oceans. Observations suggest that both ocean warm- ing and ice mel are contributing to increasing rates of average global sea level rise (Bindoff et al. 2007). The average temperature of the global ocean has increased to depths of at least 3,000 meters, and observations show that the ocean has been absorbing more than 80 percent of the heat added to the climate system (Williams et al. 2009). This warming causes seawa- ter to expand and sea levels to rise. In addition, mountain glaciers and snow cover have declined on average in both hemispheres, and losses from the Greenland and Antarctic ice sheets have very likely contributed to global sea level rise between 1993 and 2003 (Williams et al. 2009). Photo: Alligator River National Wildlife Refuge, beyondseasonsend org Land subsidence, both natural and human- caused, is the gradual downward settling of the Earth's surface (Williams et al. 2009). Groundwater removal, drainage of organic soils, and underground mining can all contribute to subsidence, leading to signifi- cant damage and increasing risk from flooding due to sea level rise. Subsidence is also caused by a vari- ety of natural factors including tectonic processes, sediment loading and compaction, and the extrac- tion of subsurface fluids such as oil and water. Both local subsidence and global mean SLR determine the relative sea level rise experienced at a particular loca- tion. On the Atlantic coast of North America, the Earth's crust is actually relaxing vertically, or sinking downward (Engelhart et al. 2009). Relative SLR is therefore measured with respect to a specific verti- cal point or line used as a reference in a particular location and can be measured directly by coastal tide gauges, which record both the movement of land to which the gauge is attached and the changes in global sea level rise. Relative SLR is already evident in many coastal regions and will increase significantly during this century (Bindoff et al. 2007), Williams et al. 2009), further magnifying the effects of global SLR resulting from thermal expansion and melting.