Sea level rise

Coastal habitats are critical areas for many important fish and wildlife species in Massachusetts. Estuaries, salt marshes, and other coastal waters provide nursery grounds and summer habitat for many ecologically and economically valuable predatory fishes and their prey. In addition, coastal marshes, grasslands, rocky and sandy shores, uplands and dunes are key breeding and nesting areas for seasonal migratory coastal birds and other wildlife. Coastal habitats also serve as transition zones for migratory (anadromous and catadromous) fishes that move between salt and fresh waters. Coastal habitats and the species that depend upon them are some of the most vulnerable to climate change due to a variety of threats, including changing temperatures, changes in sediment and nutrient delivery from upstream habitats, more acidic ocean waters, more severe coastal storms, and, perhaps most notably, rising sea level.

Global sea levels have already risen by approximately 8 inches since 1900
The Northeast United States exceeds the global average with sea levels increasing by approximately 12 inches since 1900
Between 1921 and 2014, sea levels have risen in Boston, Massachusetts by 0.11 inches per year for a total of 11.04 inches in 100 years
The Northeast coast is especially vulnerable to flooding because of its low slope coastal areas
Sea level rise increases the risk from threats such as coastal erosion, flooding, and salt water intrusion into terrestrial and freshwater habitats

Projected Sea Level Rise

It is almost undeniable that sea level will continue to rise and accelerate over the coming century. Mid-century projections suggest much of the region will experience between 8 and 30 inches of sea level rise relative to sea levels during the early 2000s. Sea level projections towards the end of the century vary from 18 to 72 inches. Exactly how much sea level rise Massachusetts can expect varies based on emission scenarios, changing oceanic processes (e.g., circulation patterns), and most importantly, uncertainty about the amount of new water going into the oceans from the melting of land-based ice sheets, such as those in Greenland and Antarctica. Melting of floating ice such as Arctic sea ice and icebergs is already accounted for in future projections and does not alter the sea level. A great analogy is ice cubes in a glass of water: if you add an ice cube to a glass of water (i.e., land-based ice), the water level goes up; but when existing ice in the glass (i.e., floating ice) melts, the level stays the same.

Coastal Storms

Changes in the freqency and intensity of coastal storms, such as summertime tropical cyclones, hurricanes, and wintertime “Nor’easters” combined with rising sea levels increases the vulnerability of coastlines and coastal habitats. Sea level rise impacts can penetrate far inland into our tidal estuaries. Therefore, saltwater intrusion into coastal ecosystems and aquifers are very likely to be an issue of increasing concern. Furthermore, in low lying areas, rainfall flooding may become worse not only due to heavier rain events, but because high sea levels will reduce drainage to the ocean. This may enhance pollution impacts on fish and wildlife in affected areas, especially in (formerly) industrial sites.

Advances in Sea Level Rise Modeling

Our understanding of how coastal habitats will respond to sea level rise has been limited, but is improving. To date, most models that project the impacts of sea level rise have simply estimated the amount of flooding or inundation due to sea level rise and storm surge. While this is realistic for hard shorelines, like rocky coasts or human-developed or engineered areas, habitats like salt marshes, sandy beaches, and barrier islands have the ability to respond to rising waters more actively in undeveloped areas. Newer sea level rise models are beginning to predict these more dynamic responses by combining sea level rise projections with factors including land cover type, coastline elevation or topography, and vertical land movement rates due primarily to glacial subsidence and rebound (i.e., when the weight of a glacier leaves land, the land is able to 'rebound' to a higher elevation). These new models show much promise in gaining a better and more realistic understanding of how local habitats will be impacted and respond to sea level rise in Massachusetts. Additional information on other types of sea level rise models, ranging from visualization (e.g. NOAA's Sea Level Viewer) and inundation (i.e. "bathtub") models (e.g. SLAMM) to dynamic coastal response models (e.g. Coastal Landscape Response to Sea-Level Assessment), can be found in the Resources list below.