There is much concern over rising sea levels and disappearing coastline. Yet how are such changes really measured?
Satellites
can measure tiny changes in sea levels referenced to a known baseline,
but those measurements have only been available since 1993. Two other
methods used for changes occurring over more than 100 years are tide
gauges and efforts by the United Nations' Intergovernmental Panel on
Climate Change (IPCC) in computer modeling.
A tide gauge monitors
water level changes in relation to a local reference height. They are
simple devices, not too different from a pingpong ball floating in a
tube. Tide gauge data are available for more than 1,750 stations around
the world and are the longest time series available. In the case of
Delaware, records go back to the early 20th century, while in places
such as Amsterdam they go back to the late 17th century.
How reliable are such data?
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