35
month, a year, a decade, a century, or perhaps even a few millennia? How would sea
level change on those different timescales along the coast of North Carolina and
what physical processes would cause the changes that you observed? And since
nobody sat on the dock for the past ~2000 years and there were no instruments making measurements, how do we know that sea-level in North Carolina did change?
An important definition must be made before we can proceed any further. The
key quantity that we are interested in is relative sea level, which is the height of the
sea-surface with respect to the land. In short, it is what the passive observer on the
dock in North Carolina would observe and, crucially, it can change because the sea
and/or land surface moved up/down as a consequence of many different physical
processes. To complicate matters, the sea and land can move in the same direction,
opposite directions, or not at all, depending on the time and place where the observations are made. This means that in our example from North Carolina, relative
sea-level changes through time and the causes of those changes will depend on what
timescale we are interested in (minutes to millennia). Furthermore, it means that
relative sea level can (and does) vary across space, such that relative sea-level trends
in North Carolina are not always, if ever, the same as those elsewhere (for example,
in South Carolina, South Africa, or Singapore).
Sea-level rise will be one of most widespread, costly, and difficult to manage
effects of the climate changes predicted for the remainder of the twenty-first century
and beyond. To accurately predict local sea-level rise (since this, not the global average, is the quantity that matters to the people and organizations tasked with managing our coasts and planning for future changes) requires an understanding of how
and why relative sea-level can vary through time and across space. The trajectory of
socio-economic impacts caused by sea-level rise will not be an abrupt change from
“dry” to “flooded”, but rather a step-wise progression of worsening and more frequent effects.
Imagine a building in a coastal community, perhaps a private home or a piece of
expensive public infrastructure such as an airport or a power station. It was likely
constructed to be above and beyond the reach of floods from the ocean. As relative
sea level rises, tides, waves, and storms are carried to higher elevations and further
inland. The first impact on our building is likely to be anomalous flooding during a
(near) worst-case scenario when large waves during a major storm arrive during a
particularly high tide. We might think of how Hurricane Sandy impacted New York
City as an example.
Continued relative sea-level rise will make such events more common because it
ceases to be necessary to have all of the factors align in time and space to cause
flooding. As more time goes by even unusually high astronomical tides without
waves and storms may begin to flood the building. This phase is sometimes called
“sunny day” or “nuisance” flooding and can currently be seen impacting locations
such as Annapolis by closing roads on predictable days. Ultimately, our location
will be impacted by every tide and, eventually, complete flooding will occur. The
amount of time that elapses between these phases depends on the rate of relative
sea-level change and the impact will depend on the anticipated lifespan of the building compared to the time frame of relative sea-level rise.
3 Time and Tide Wait for No Man
month, a year, a decade, a century, or perhaps even a few millennia? How would sea
level change on those different timescales along the coast of North Carolina and
what physical processes would cause the changes that you observed? And since
nobody sat on the dock for the past ~2000 years and there were no instruments making measurements, how do we know that sea-level in North Carolina did change?
An important definition must be made before we can proceed any further. The
key quantity that we are interested in is relative sea level, which is the height of the
sea-surface with respect to the land. In short, it is what the passive observer on the
dock in North Carolina would observe and, crucially, it can change because the sea
and/or land surface moved up/down as a consequence of many different physical
processes. To complicate matters, the sea and land can move in the same direction,
opposite directions, or not at all, depending on the time and place where the observations are made. This means that in our example from North Carolina, relative
sea-level changes through time and the causes of those changes will depend on what
timescale we are interested in (minutes to millennia). Furthermore, it means that
relative sea level can (and does) vary across space, such that relative sea-level trends
in North Carolina are not always, if ever, the same as those elsewhere (for example,
in South Carolina, South Africa, or Singapore).
Sea-level rise will be one of most widespread, costly, and difficult to manage
effects of the climate changes predicted for the remainder of the twenty-first century
and beyond. To accurately predict local sea-level rise (since this, not the global average, is the quantity that matters to the people and organizations tasked with managing our coasts and planning for future changes) requires an understanding of how
and why relative sea-level can vary through time and across space. The trajectory of
socio-economic impacts caused by sea-level rise will not be an abrupt change from
“dry” to “flooded”, but rather a step-wise progression of worsening and more frequent effects.
Imagine a building in a coastal community, perhaps a private home or a piece of
expensive public infrastructure such as an airport or a power station. It was likely
constructed to be above and beyond the reach of floods from the ocean. As relative
sea level rises, tides, waves, and storms are carried to higher elevations and further
inland. The first impact on our building is likely to be anomalous flooding during a
(near) worst-case scenario when large waves during a major storm arrive during a
particularly high tide. We might think of how Hurricane Sandy impacted New York
City as an example.
Continued relative sea-level rise will make such events more common because it
ceases to be necessary to have all of the factors align in time and space to cause
flooding. As more time goes by even unusually high astronomical tides without
waves and storms may begin to flood the building. This phase is sometimes called
“sunny day” or “nuisance” flooding and can currently be seen impacting locations
such as Annapolis by closing roads on predictable days. Ultimately, our location
will be impacted by every tide and, eventually, complete flooding will occur. The
amount of time that elapses between these phases depends on the rate of relative
sea-level change and the impact will depend on the anticipated lifespan of the building compared to the time frame of relative sea-level rise.
3 Time and Tide Wait for No Man