![]() ![]() The emergence of remote sensing techniques and the global Argo program has allowed closure of the sea level budget over the last decade by direct observations of mass and steric components, both on global and regional scales. On regional scales, large deviations from the global mean trend are observed, as well as significant variability on interannual and decadal scales. Roads, bridges, subways, water supplies, oil and gas wells, power plants, sewage treatment plants, landfills-virtually all human infrastructure-is at risk from sea level rise.Sea level rise is one of the most important consequences of climate change. In urban settings, rising seas threaten infrastructure necessary for local jobs and regional industries. Sea level rise at specific locations may be more or less than the global average due to local factors such as land subsidence from natural processes and withdrawal of groundwater and fossil fuels, changes in regional ocean currents, and whether the land is still rebounding from the compressive weight of Ice Age glaciers. ![]() Globally, eight of the world's 10 largest cities are near a coast, according to the U.N. In the United States, almost 40 percent of the population lives in relatively high-population-density coastal areas, where sea level plays a role in flooding, shoreline erosion, and hazards from storms. With continued ocean and atmospheric warming, sea levels will likely rise for many centuries at rates higher than that of the current century. The ocean is absorbing more than 90 percent of the increased atmospheric heat associated with emissions from human activity. The two major causes of global sea level rise are thermal expansion caused by warming of the ocean (since water expands as it warms) and increased melting of land-based ice, such as glaciers and ice sheets. ![]() coastal communities than it was just 50 years ago. Disruptive and expensive, nuisance flooding is estimated to be from 300 percent to 900 percent more frequent within U.S. Higher sea levels mean that deadly and destructive storm surges push farther inland than they once did, which also means more frequent nuisance flooding. In 2014, global sea level wasĢ.6 inches above the 1993 average-the highest annual average in the satellite record (1993-present). ![]() Global sea level has been rising over the past century, and the rate has increased in recent decades. Taken together, these tools tell us how our ocean sea levels are changing over time. Satellite measurements provide us with the average height of the entire ocean. Tide stations around the globe tell us what is happening at a local level-the height of the water as measured along the coast relative to a specific point on land. Sea level is primarily measured using tide stations and satellite laser altimeters. Sea level rise at specific locations may be more or less than the global average due to many local factors: subsidence, upstream flood control, erosion, regional ocean currents, variations in land height, and whether the land is still rebounding from the compressive weight of Ice Age glaciers. Just as the surface of the Earth is not flat, the surface of the ocean is also not flat-in other words, the sea surface is not changing at the same rate globally. Global sea level trends and relative sea level trends are different measurements. What's the difference between global and local sea level? ![]()
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