Sea Level Rise

Within the next century—and possibly sooner—many of the Earth's coastal cities and agricultural lands will be at extreme risk because of the effects of the rising level of the planet's seas. Sea level rise, defined as the amount of increased volume of ocean, is caused by several factors and may eventually result in the flooding and erosion of coastlines and associated low-lying areas across the world. Some varied locations at high risk include cities such as New York City; Cape Lookout, North Carolina; London; Singapore; Galveston, Texas; New Orleans; and areas such as the Florida keys, Bangladesh, the Netherlands, the Maldives, and many other island nations, such as Kiribati, where evacuations have already begun. The causes of sea level rise include, but are not limited to, the following:

• Thermal Expansion: Caused by warming seas and water expansion upward, the primary cause of thermal expansion is global warming, the trapping of greenhouse gases within the atmosphere, and the resulting expansion in volume.
• Ice Melt: Also the result of warming, ice melt causes waters to rise as glaciers and ice caps melt, adding water to the seas.
• Ocean Current Variations: An example of ocean current variations is El Niño, which is a natural and seasonal surface occurrence that “stacks” seawater. This results in sea level rise because of the movement of warmer water flowing into higher latitudes, where cooler water lies.
• Natural Variation in Sea Levels: Variation can be up to two meters at different spots on the globe, as indicated by topographical studies and interpreted as an additional indicator of rising seas.

Scientists report a consensus in which they expect the rise in sea level to be 60 to 90 centimeters by 2100. Over the past 100 years along the U.S. Atlantic Coast, reported sea levels have risen 30 to 40 centimeters, which is higher than the average sea level rise around the globe. Because the sea is not at a consistent, even level and in its natural state, it rises at uneven rates around the globe. In some areas sea level has risen above the mean, and in other areas it has actually fallen below the mean sea level.

Scientists now agree that the Intergovernmental Panel on Climate Change (IPCC) report of 2007 underestimated the rate of sea level rise. Scientists believe that sea level is rising faster than the IPCC prediction because the panel failed to account for the melting of landed ice sheets in Greenland and the Antarctic. Since the IPCC report, scientists have documented an increased melting rate in those locations, with 2009 observations noting movement of 125 feet per day in one Greenland glacier. It has also been recorded that the rate of mountain glacier melting has itself increased, also affecting the rise in sea level around the globe. Sea level rise is also occurring at a faster rate over the years, with a rise of 3 or more millimeters a year since 1993. Historical records indicate a rise of close to 20 centimeters since 1880, and that the warmer the sea gets as a result of climate change, the faster it rises.

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