AS STIPULATED IN NC Session Law (SL) 2012-202, the NC Coastal Resources Commission’s Science Panel released an “updated” Sea Level Rise Assessment Report on March 31 (it’s actually a complete re-write). The report will be finalized in early 2016 subsequent to an extended public comment period and delivered to the NC General Assembly by March 1, 2016. Concordantly, and as provided in SL 2012-202, the Coastal Resources Commission will also be assessing the economic and environmental costs/benefits of developing, or not developing sea level rise regulations and policies between now and the aforementioned March 1, 2016 deadline.
That’s a lot of groups directing or preparing reports, so let’s briefly review them before going any further – (1) General Assembly = your state elected House and Senate representatives, (2) Coastal Resources Commission, or “CRC” = a 13-member group that is the rule and policy-making arm for coastal development pursuant to the Coastal Area Management Act (CAMA). They are appointed by the governor, speaker of the house, and the senate president pro tempore by law. (3) Science Panel = a voluntary, advisory group of currently 10 engineers and scientists appointed by the CRC.
In essence, SL 2012-202 created a reporting framework whereby the Science Panel would conduct a comprehensive review of scientific literature and available North Carolina data to address the full range of global, regional and North Carolina specific sea level change (past, present and future). Moreover, the Science Panel was also mandated to address regional sea level differences observed up and down the state’s coastline. The CRC subsequently provided additional reporting guidance, which was highlighted by establishing a 30-year future time table and creating an outside technical peer-review process. At the end of the day, the draft Sea Level Rise Assessment Report reviews the data and processes responsible for sea level movement in the past and present and provides three plausible scenarios for 2045 (but does not advocate for any particular scenario) consistent with the 30-year time table concept mentioned immediately above (2015-2045).
The draft report is available at portal.ncdenr.org/web/cm/sea-level-rise-study-update and you must be wondering what this 42-page document says after this long-winded introduction. If I had to bullet point the main components of the report, then it would go something like the following;
(a) Climate has been warming and sea level has been rising since the last Ice Age ended about 20,000 years ago.
(b) The rate of melting ice and rising seas was rapid at first but has generally stabilized in the past few thousands of years – “stabilized” is a relative term of course and sea level is still rising nonetheless. The amount of sea-level rise or fall attributable to the changing volume of water in the ocean’s basins is termed Global Sea Level.
(c) Vertical land motion is prevalent in North Carolina and can be readily documented when analyzing the state’s tide gauge record or the sedimentary record within the coastal plain. The buzz words for the sinking or rising of land is “subsidence” and “uplift” respectively. Sinking land coupled with a rising sea will result in an enhanced sea level rise if you will, while conversely, rising land and a rising sea level will result in a lower sea level rise. Or in certain areas of the world, the land may be rising at the same rate as Global Sea Level, which would result in no visible sea level rise at all. This is where/when the term Relative Sea Level comes into play – it’s the measurement of the sea surface elevation relative to a local datum. Importantly when scientists review tide gauge and satellites altimetry readings, they are recording Relative Sea Level.
(d) There are two main drivers impacting land motion (and without getting too technical); (1) the topography of the hard crystalline rock way underneath our feet slipped when America and Africa separated from one another as the Atlantic Ocean formed. Millions upon millions of years later, thick or thin layers of riverine, estuarine and marine sediments have been deposited in the lows and highs of the rock surface, respectively. The thick areas of sediments located within deep depressions of the rock surface have a greater propensity to sink, while the converse is true for the thin areas located in areas where the rock surface is high. (2) The earth’s surface has moved “up and down” in response to the melting of heavy and thick ice sheets (miles high in some places). The up and down movement depends on your position relative to the thickest part of the ice sheet, toward its periphery, and the land that was first pushed upward like a bulldozer blade in front of the ice sheet that is sinking now. This nifty map (Fig. 1) from the Science Panel Report partitions the North Carolina coast into regions based on these factors – basically the land is sinking (therefore higher relative sea level) in the north and not as much or even rising in the southern part of the State (less relative sea level).
(e) The location and record length of the tide gauges in the state, albeit not perfect, does provide a rich record of sea level change. The Science Panel Report used data from five gauges extensively and the vertical land movement component at each gauge was determined as well.
(f) Moving forward over the course of the next three decades (2015-2045), the Science Panel keeps the rate of vertical land motion the same and presents three plausible options for sea level rise at each of the five tide gauges. Option 1 keeps the present rate of sea level rise exactly the same for the next 30 years. Options 2 and 3 utilizes the Intergovernmental Panel on Climate Change’s (IPCC’s) most recent report by taking the lowest and highest ranges of predicted sea-level rise they provided. The IPCC forecast was generated using a complex process-based model taking greenhouse gas emissions into account. Granted, as with any model and any future prediction, there will be uncertainty; but as a colleague of mine once said – it’s ROM (Rough Order of Magnitude) and that might be the best we can do for now.
The Science Panel Report is to be updated every 5 years so we can keep track and adjust accordingly. All three of the 30-year options/scenarios are presented in Fig. 2. In short; if we just keep the same rate of rise until 2045, then the range is 1.9 inches for Southport/Wilmington and 6.4 inches for Duck. If we look at all three options, the minimum is 1.9 inches of rise by 2045 in the Southport/Wilmington area (no surprise) and a maximum of 10.6 inches in the Duck area.
So what’s next? The Science Panel Report is envisioned to be a resource document and as mentioned in the introduction, the Coastal Resources Commission is entrusted with the decision to advance sea-level rise regulations on a state level. Of course local governments also have the liberty to use the report as they deem fit. Again, the report is available for public comment for the next several months, and any science or policy concerns you may have should be articulated and submitted to the NC Division of Coastal Management’s coastal and ocean policy manager, Tancred Miller at Tancred.Miller@ncdenr.gov.
*For the full sake of disclosure, I currently serve on the Science Panel and helped prepare the report.