 Within
the next 60 years, coastal erosion may claim one out of four houses
within 500 feet of the U.S. shoreline.[1]
Coastal erosion is caused by rising sea level, powerful ocean waves,
large storms, and flooding.[2] Coastal erosion
affects businesses, homes, public facilities, beaches, and bluffs
close to the ocean or Great Lakes.
Inasmuch
as paleo-environmental and historical data have clearly indicated
the occurrence of sea-level changes in the past, new scientific
information on the nature and causes of sea-level change- and the
development of a quantitative predictive capability- are of utmost
importance for the future. This topic is inherently an interdisciplinary
science problem addressed within NASA by the Cryospheric Science,
Ocean Science, Hydrology, and Solid Earth Science Programs.
The
10–20 cm global sea-level rise recorded over the last century
has been broadly attributed to two effects: the steric effect (thermal
expansion and salinity-density compensation of sea water) of changes
in global climate, and mass-budget changes due to a number of competing
geophysical and hydrological processes in the solid Earth-atmosphere-hydrosphere-cryosphere
system. While the steric effect is primarily a climatic issue, the
Solid Earth Science Program is poised for a fundamental contribution
by separating the two effects via a combined use of space geodetic
measurements of sea-surface topography and timevariable gravity.
The
mass-budget changes include water exchange from polar ice sheets
and mountain glaciers to the ocean, atmospheric water vapor and
land hydrological variations, and human effects such as water impoundment
in artificial reservoirs and extraction of groundwater. These exchanges
are all superimposed on the vertical motions of the solid Earth
due to tectonics, rebound of the lithosphere from past and present
deglaciation, and other local ground motions. A number of space
geodetic measurements of sea-surface topography, ice mass, gravity,
and ground motions are directly relevant. A complete knowledge of
sea-level change will then emerge and be used for the development
of predictive global and regional models.
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