Looking back at Sea Level : Caution, objects may be bigger

How big is your rear-view mirror? Most of the time, professionally in water resources, my rear view mirror is big enough to see the last 90 years. This is the time period for most of the USGS gage data that I use for different projects.

A couple weeks ago I watched a video on Google Hangout (I do hate that name) about sea level rise. They discussed how much and how fast will sea level rise in the coming decades and what makes sea level rise hard to predict. Participants included:

  • Josh Willis, NASA’s Jet Propulsion Laboratory
  • Sophie Nowicki, NASA’s Goddard Space Flight Center
  • Mike Watkins, NASA’s Jet Propulsion Laboratory
  • Virginia Burkett, U.S. Geological Survey
  • Andrew Revkin, Pace University & New York Times Dot Earth blogger

One graph they presented in particular caught my attention. This is one of those rear-view graphs that reminded me of one of my graphs that I use when talking about climate variability. In my graph, I use downloaded tree ring data to show a twenty year drought here in South Carolina in the 1750s and ask what that drought would feel like today.

The graph NASA presented was a 2,000 year record of sea level from North Carolina. I did a little research this weekend on the origins of this graph (again thank you Google).

For this graph, scientists used microfossils called foraminifera—or just forams—as a proxy. They were preserved in sediment cores extracted from coastal salt marshes in North Carolina. Why use forams? They lived in tidal inundation areas and were able adjust to sea-level rise. The ages of the cores were estimated using radiocarbon dating and other techniques.

The team compared their results with tide-gauge measurements from North Carolina over the past 80 years, and global tide-gauge records from the past 300 years. It matched well. They even had to adjust the data to take into account the fact that apparently the Outer Banks of North Carolina are sinking (1.0 mm/year), a term they called “glacial isostatic adjustment”.

Sea Level Rise Graph 2000 years

The graph shows four phases of sea-level change

  • Sea level was stable from at least BC 100 until AD 950
  • Sea level, then increased for 400 y at a rate of 0.6 mm/y, in the 11th century known as the Medieval Climate Anomaly
  • Period of stable, or slightly falling, sea level that persisted until the late 19th century, known as the Little Ice Age
  • Since then, sea level has risen at an average rate of 2.1 mm/y, representing the steepest century-scale increase of the past two millennia. This rate was initiated between AD 1865 and 1892

I think looking at sea level rise through those graphs forced me to think more about the future. While there is much uncertainty going forward with sea level projections for the next century, varying from 1 foot to 6 feet, coastal communities need work on their own process to deal with this risk. In NOAA’s 2012 report titled Incorporating Sea Level Change Scenarios at the Local Level, they suggested the following:

When it comes to planning for sea level change impacts, the “one-size-fits-all” approach is not realistic. There are simply too many scientific variables, risk perceptions, and political implications unique to each location to consider. For this reason a scenario approach is preferred. Considering a range of possibilities lets community members and officials incorporate appropriate variables for their community when deciding how to best prepare for the future.

Remember you can drive without a rear-view mirror, but at some point something big may hit you from the back or side. So the question for a coastal community would be how comfortable are you with that risk?