Even climate change skeptics can't dispute the evidence which shows that regional sea level rose approximately one foot over the last century. That's the highest rate in 3,000 years, according to a recent study on sea level rise in Pleasant Bay conducted by the Center for Coastal Studies in Provincetown under the auspices of the Pleasant Bay Alliance. In another century we may be nostalgic for that historic sea level rise rate. In 2013 the Intergovernmental Panel on Climate Change estimated that in the next century, sea level for the New York City and southern New England region could increase by as much as three feet. The recent report pegs the increase in Pleasant Bay at between 1.2 feet and 2.9 feet by 2100.
This accelerated increase in the level of the ocean waters will have two significant impacts on the 9,000-acre bay, according to the report. It will shorten the duration of the barrier beach cycle that for centuries has governed the periodic breaching and growth of the Nauset Barrier Beach – North Beach in Chatham – which forms a protective arm around the bay. Instead of 140 to 150 years, the cycle will play out in as little as 70 years, meaning more incidents of beach overwash and breaching, changing inlets and potential for significant erosion of the inner shoreline.
Secondly, that inner shoreline of the bay will lose between a quarter and a half of its 392 acres of intertidal area, and beach between low and high tide. In a healthy system, the intertidal area needs to be able to respond to storms and changing water levels by moving both landward and seaward. However, the presence of revetments, built to protect the upland from washing away, will prevent the beach from moving west, resulting in the loss of intertidal resources such as tidal flats and salt marsh which are vital to the health of the bay and its inhabitants.
These effects may seem somewhat abstract, but they point to a major concern of members of the Alliance, which is composed of representatives from Chatham, Harwich, Orleans and Brewster: How to balance the need to allow the system the flexibility required to function under the sea level increase scenarios while protecting both private property and public infrastructure. The good news is that even under the three-foot worst case sea level rise prediction, the bay and the barrier beach system will remain intact. The bad news is that they could change significantly and have widespread negative impacts on a range of concerns, from habitat to pollution to access to town landings and even the open waters.
Forewarned is forearmed, and the report puts town officials on notice that these are issues they need to consider as they develop management plans for the bay and public infrastructure within the system. Regarding erosion, the Alliance has also released management guidelines that will help conservation commissions and property owners understand the impacts of the range of shoreline protection measures available. Officials in the bay towns should ensure that these play a prominent role in discussions of proposals for revetments and other structures that could have far-reaching impacts on the bay's resources.
We urge residents to download and read the sea level rise report; it is not alarmist and provides an understandable, scientific explanation for its conclusions. It can be found at pleasantbay.org; there is also a link on our website. The future of Pleasant Bay depends on how we react now to the changes likely to happen in the future.