ACTIVITY STREAM:	Observe, Data, Process, Model
SCIENCE ELEMENT:	Solid Earth Processes


SCIENTIFIC MERIT:  Any substantial rise in sea level due to global warming 
will have a severe impact on low-lying coastal areas and oceanic islands. 
Mitigation of the effects of rising sea level on developed coastal regions 
(barrier islands, river estuaries, and deltas) over the short term would 
involve a large monetary investment in shoreline stabilization; over the long 
term, strategic retreat becomes necessary, with large economic costs and 
widespread social disruption. Prudent formulation of national and 
international public policy with respect to future sea level change requires a 
solid scientific understanding of the trend in absolute sea level in the decadal 
time frame, and how local or regional tectonics may counter or amplify 
worldwide sea level change. In order to achieve this understanding, NSF 
plans to systematically expand its program in space-based geodesy using the 
Global Positioning System. This will result in strategically-placed geodetic 
networks at coastal locations and in places of tectonic activity. Through 
analysis of data from these networks, long-term trends in sea level due to 
glacial melting and ocean expansion can be distinguished from effects of post-
glacial rebound and active tectonics. Analysis of data from coastal locations 
will be supported by analysis of data from tide gauges and absolute gravity 
instruments. Analysis of relative motions due to active tectonics in the 
vicinity of plate boundaries will be supported by investigations involving the 
deployment of portable seismic arrays. Basic scientific investigations of 
internal processes within the solid Earth, coupled with well-distributed 
observations, careful data processing, and the development of long time 
series, are essential for an understanding of this important form of global 
STAKEHOLDERS: NSF's global geodetic program, which forms the basis for 
its support of studies of sea level change, is linked to NOAA's in situ global 
sea level network, NASA's satellite ocean topography experiment 
(TOPEX/Poseidon), and the space geodetic programs of the three agencies for 
high resolution measurement of both tectonic and climate-induced sea level 
change. NSF supports GPS investigations through the University NAVSTAR 
Consortium (UNAVCO), which has an international membership; a 
substantial fraction of the currently-supported projects are outside the U.S., 
and involve cooperation with the national geodetic agencies of other 
countries. NSF's program of studies of contemporary sea level change is 
strongly coupled with stratigraphic and geomorphological studies within the 
Earth System History element aimed at understanding the longer-term causes 
of sea level change in the glacial and pre-glacial past. Thus, sea level studies 
support two elements of the global change program. The studies also support 
a proposed Core Project of the IGBP, Land-Ocean Interactions in the Coastal 
Zone, Research Focus 3: Responses to changes in relative sea level. The 
program is linked studies of ecosystem dynamics under changing 
environmental conditions being carried out through the Land Margin 
Ecosystems Research (LMER) program, and to the coastal environments 
programs of other U.S. agencies (DOI, NASA, DOD). It is further linked to the 
West Antarctic Ice Sheet (WAIS) initiative with regard to the potential impact 
of future instability of this ice sheet on sea level. 
POLICY RELEVANCE:  The long-term policy payoff of extracting the climate-
induced sea level signal requires continuous, accurate time series from 
globally well-distributed geodetic marks. Thus, there is much short-term 
policy benefit in early establishing of such marks, in collaboration with 
international partners, along with support for research in data processing and 
analysis, which will provide a basis for policy judgments in the shortest 
possible time concerning how fast control measures must be implemented. In 
the short term, this activity is directly relevant to policy issues within the 
areas of Climate Change and Global Warming (in the contest of natural 
variability)  and International Cooperation. Over the longer term, it is 
relevant to most of the "interactions" aspects of Human Dimensions and 
Economics as currently defined.
PROGRAM CONTACT:  Michael Mayhew, Geophysics Program Director