Island nations, such as Maldives and Comoros, are particularly at risk. Sea-level rise threatens low-lying areas around the world. Hence, from a policy coastal-management perspective the crucial questions that need to be addressed are: (1) for how long a given atoll island is safe from mean sea-level rise and associated. This phenomenon is called sea-level rise. Melting ice sheets cause an elevation in sea level. Global warming, the current period of climate change on Earth, is causing glaciers and ice sheets to melt. At the peak of the most recent ice age, about 18,000 years ago, sea level was perhaps 100 meters (300 feet) lower than it is today. During past ice ages, sea level was much lower because the climate was colder and more water was frozen in glaciers and ice sheets. Changes in Sea Level Sea level may vary with changes in climate. Local mean sea-level measurements are a combination of sea-level variations and movement of the land. That same land bounces back (a process called postglacial rebound) if the ice retreats, or melts, and its weight is removed. For example, the tremendous weight of a glacier on land pushes the land down, closer to sea level. Just like the ocean, the elevation of land may rise and fall over time.

Sea level is measured in relation to the adjacent land. The flood that has a 1-percent probability (1 in 100) of being equaled or exceeded in any given year is often re-ferred to as the 100-year flood. The BFE is the elevation (to the tenth of a foot) that has a 1 chance of flooding each year, or a 26 chance of flooding over the term of a thirty year. Flood frequency Probability, expressed as a percentage, that a flood of a given size will be equaled or exceeded in any given year. It also averages out the effects of local weather and oceanographic conditions. Flood elevation Height of flood waters above an elevation datum plane. It enables scientists to account for the long-term variations in the moon's orbit. The 19-year period is called a Metonic cycle. In the United States and its territories, local mean sea level is determined by taking hourly measurements of sea levels over a period of 19 years at various locations, and then averaging all of the measurements. So the surface of the ocean can be used as a base for measuring elevations, the concept of ' local mean sea level' has been developed. However, winds, currents, river discharges, and variations in gravity and temperature prevent the sea surface from being truly level. Estimated Base Flood Elevation (BFE) viewer for property owners, community officials and land developers to identify the flood risk (high, moderate, low). Because the ocean is one continuous body of water, its surface tends to seek the same level throughout the world. Sea level is the base level for measuring elevation and depth on Earth.

Base flood elevation sea level