Coastal Marshlands Can Adapt to (Some) Sea Level Rise

Three things you need to know:

—New research shows that some coastal marshlands will not survive rapid sea level rise to 2100, though some may be able to adapt if sea levels change slowly.

—Some amount of sea level rise by 2100 is inevitable, scientists say, but the possible range —between one and five feet — heavily depends on future greenhouse gas emissions.

—The survival of coastal marshlands could play an important role in absorbing a lot of the carbon dioxide (CO2) emitted by human activity.

The marshes of Plum Island Estuary are among those predicted by scientists to submerge during the next century under conservative projections of sea-level rise. Credit: Matthew Kirwan, USGS. 

The Debrief:

Scientists often point to sea level rise as one of the unavoidable consequences of global warming. They are not exactly sure how much the ocean will rise in the next 100 years — or how quickly — but they expect somewhere between one to five foot increase by the end of this century. Because there is no way to avoid some sea level rise as global temperatures go up, researchers are now trying to better understand how coastlines will respond as the waters creep upward.

Anticipating how wetlands and marshes along the coast might adapt turns out to be particularly tricky. Marshes can rise or sink in response to changes in sea level, depending on how much sediment is in the area and how easily it can move around. Yet even though wetlands have some ability to adjust themselves, a new study shows that if the sea rises rapidly in the next century, most marshy areas won’t have time to adapt and may be lost altogether.

According to research conducted by scientists from the U.S. Geological Survey (USGS), a relatively fast rise in sea level during the next century will put most wetlands completely underwater by 2100. On the other hand, the same models show that if sea level rise is slower (which could happen if global warming slows down), some wetlands with high sediment levels will rise up along with water levels and won’t get swallowed up by rising seas.

In their paper published in the journal Geophysical Research Letters, the authors point out a number of American wetland areas that are vulnerable to sea level rise no matter what happens; marshes in Massachusetts’s Plum Island Estuary and North Carolina’s Albermarle-Pamlico Sound are particularly threatened by even moderate sea level rise, and could drown by 2100.

Why this science matters:

When trying to predict which coastal areas are most threatened by climate change, researchers have been limited to looking at the coast as a static landscape that won’t change as the waters rise. But scientists that study marshes have known for a long time that changes in sea level can actually influence the levels of the marsh itself. In this recent study, the researchers have begun to incorporate that understanding in their predictions of how wetlands will weather the kind of sea level rise climate scientists are now predicting. As the authors note, the existence and survival of coastal marshlands is not solely dependent on how much sea level rises, but “instead depends strongly on the magnitude of the 21st century climate change” and how quickly sea level changes as global temperatures increase.

Losing coastal wetlands would, of course, threaten the plants and animals that call marshes home. In fact, it’s unclear that many species would be able to relocate and recover if most American coastal wetlands were underwater by 2100. In addition to hosting unique species, wetlands also protect inland areas by absorbing the force of wind-driven storm surges.

But the threat to wetlands from sea level rise also poses a problem for our planet’s ability to stave off further global warming. Some recent research from Conservation International shows coastal marshes contribute to storing a lot of the CO2 human activity is producing. This so-called “blue carbon,” or the carbon that is stored in wetland grasses and marshy sediment, may be stored up to 50 times more rapidly than in areas like tropical forests. A full analysis of how blue carbon can help mitigate future climate change (i.e., by storing massive quantities of CO2 in marshes) hasn’t yet been given a detailed review by the scientific community, or been included in reports from the U.N. Intergovernmental Panel on Climate Change.