Global warming bringing L.I. down and sea levels up
Scientists model local impacts on towns and tidal environments
11 comments below
What are the possible consequences? That is something Conservancy scientists Sarah Newkirk, a coastal team leader, and Nicole Maher, a wetlands specialist, aim to figure out and model for Long Island's decision makers, including town, county and state officials, regulators and planning agencies.
According to their research, the global mean sea rise for the past century has been between 1.5 and 1.8 millimeters per year. For Long Island, that number is 2.73 millimeters per year, but has increased nearly twofold to 5.2 in the past 20 years. While that might not sound like much, Dr. Newkirk's high-end projections for sea level rise are as follows: 7 inches by the 2020s, 23 inches by the 2050s and 45 inches by the 2080s. These numbers used to be thought of as low probability, high impact events, Dr Newkirk said, but, “I think the low probability part is becoming less and less true.”
While it might be a very long time before significant parts of Long Island are underwater, Dr. Newkirk said it might not be long at all before parts of the South Shore face immediate inundation. By the 2020s, Dr. Newkirk said, areas in Mastic peninsula, for example, will be inundated at high tide every day. “It doesn't mean people's houses are going to be underwater,” Dr. Newkirk said. “What it does mean is that people's basements will be wet every day.”
She answered her own question about whether that is a significant impact by saying, “It certainly would be bothersome to me.”
Dr. Maher and Dr. Newkirk pointed to greenhouse gasses as contributing to sea level rise through various mechanisms. They cause thermal expansion in the oceans, meaning that as water gets warmer, its volume increases even if the amount of water stays the same. It therefore covers a larger area than it would if it were colder.
The gasses speed up the melting of the polar icecaps. That both adds more water to the oceans, and because there is less ice and snow to reflect the sun's energy, facilitates more thermal expansion. It creates what Dr. Maher called “a positive feedback loop. More warming creates conditions that further accelerate the warming.”
And because the ice is melting, the northern part of the geologic plate on which Long Island sits is gradually rising, having been relieved of the ice caps' weight. Long Island sits on the southern end of that plate, and in a seesaw effect, as northern Canada “rebounds,” Long Island sinks further, which also helps account for its accelerated sea level rise as measured by the United States Geological Survey (USGS). The USGS tide gauge results have been “very similar” be they in the Atlantic Ocean, Long Island Sound or Peconic or Gardiner's Bay, Dr. Maher said.
Dr. Newkirk has used this information to develop an online interactive server using Google Maps to take advantage of Light Detection and Ranging (LIDAR) topographic data on Suffolk County. She plans to hold a “stakeholder workshop” next month to roll out the maps for Long Island's South Shore from the Nassau/Suffolk border to Montauk Point. Given adequate funding, she expects to expand her research into the Peconic Estuary some time late this fall.
The maps can model coastal hazard risk and sea level rise to help inform governmental decisions on planning and resource management. “It's great to have all this information on sea level rise but then what do you do as a decision maker?” Dr. Newkirk asked. She added that it would be helpful to visualize different scenarios in three dimensions rather than sifting through pages of data. When the maps are rolled out next month, she said she would happily offer additional training sessions and hoped that Long Island towns would use the data when they revise their comprehensive plans.
To be able to have the maps and projection models means “We really have no excuse for inaction,” Dr. Newkirk said. “We're able to project this. We're able to look into the future, at least a little bit. There's some uncertainty in the models. We know this is happening to some extent. We also know that the projections that we're illustrating on this project are fairly conservative.”
While Dr. Newkirk's part of the project has focussed more on development and planning, Dr. Maher's concentrates much more on resource management, particularly on salt marshes. Of them, Dr. Maher said, “These coastal wetlands support the health of our coastal ecosystem and the recreational and economic activities that depend on it.”
The marshes protect water quality, are part of the coastal food web, provide habitats for wildlife and protect upland and shoreline areas from flooding and erosion. Dr. Maher has been studying whether salt marsh growth has kept up with sea level rise. If they do not, the upper marshes convert to low marsh species and the lower marsh could become unvegetated mudflat or open water. Historically, Dr. Maher said salt marshes have kept up with sea level rise, given clean water to promote healthy marsh grass root growth and space to migrate landward. There are ongoing experiments, including one in Jamaica Bay, to determine what possible restoration strategies might be available to help marshes regain lost elevation.
These experiments were started in part because data collected on Fire Island from 2002 to 2007 show marshes there losing their race against sea level rise. The Nature Conservancy has also developed a network of Surface Elevation Tables, some of which are based in Mashomack Preserve, to identify marsh geochemistry and to determine what other processes might be contributing to the elevation shortfall. This might include marsh peat decomposition or root decay or collapse.
A marsh might be more susceptible to weakening or collapsing altogether if its root system is collecting nutrients from lawn care products that have run off either into groundwater or into the bay. Salt marshes, Dr. Maher explained, grow in low nutrient environments. They grow deep and extensive root systems in order to sustain themselves. If the nutrients are readily available, that will not happen. “They're not building that elevation to keep up with sea level rise,” Dr. Maher said. “They're not building the network that holds the marsh peat together and can resist erosion by waves or wakes.”
She recommends installation and maintenance of vegetative buffers to keep lawn care nutrients out of marshes. According to an Environmental Law Institute report, buffers of between 30 and 100 feet “will remove pollutants consistently.” It recommends longer buffer distances for steep slopes and high intensity land use.
Vegetative buffers may not seem ideal because of the property space they consume but Dr. Maher said they are better than some other options. “As sea levels rise, people are sort of more likely to want to hold on to the coast that they have,” she said. “And if they install bulkheads and other shoreline hardening structures, it may starve the marshes downstream,” creating a scalloping effect by preventing those downstream marshes from keeping up with sea level rise.
Sea level rise is real, the scientists say. Their research shows frightening possibilities. “We know that something is going to happen along these lines,” Dr. Newkirk said. “If you have that information this far in advance, we have really no excuse not to prepare ourselves and prepare our communities in a way that allows both the human community and the natural community to survive and prosper.”
The Shelter Island Reporter is pleased to offer readers the ability to comment on stories. We expect our readers to engage in lively, yet civil discourse. The Shelter Island Reporter does not edit user submitted statements and we cannot promise that readers will not occasionally find offensive or inaccurate comments posted in the comments area. Responsibility for the statements posted lies with the person submitting the comment, not The Shelter Island Reporter. Please be reminded, however, that in accordance with our Terms of Service and federal law, we are under no obligation to remove any third party comments posted on our website.