A new study shows just how significant global sea level rise could be

Since the start of the century, global average sea-level has risen by about 0.2 feet. Under moderate emissions, central estimates of global average sea-level from different analyses range from 1.4 to 2.8 more feet by 2100, 2.8 to 5.4 more feet by 2150, and 6 to 14 feet by 2300, according to the study, which appears in Annual Review of Environment and Resources.

And with 11 percent of the world’s 7.6 billion people living in areas less than 33 feet above sea level, rising seas pose a major risk to coastal populations, economies, infrastructure, and ecosystems around the world, the study says.

Sea-level rise varies over location and time, and scientists have developed a range of methods to reconstruct past changes and project future ones. But despite the differing approaches, a clear story is emerging regarding the coming decades: From 2000 to 2050, global average sea-level will most likely rise about 6 to 10 inches, but is extremely unlikely to rise by more than 18 inches.

Beyond 2050, projections are more sensitive to changes in greenhouse gas emissions and to the approaches for projecting sea-level change.

“There’s much that’s known about past and future sea-level change, and much that is uncertain. But uncertainty isn’t a reason to ignore the challenge,” says coauthor Robert E. Kopp, a professor in the Earth and planetary sciences department at Rutgers University–New Brunswick and director of the university’s Institute of Earth, Ocean, and Atmospheric Sciences.

“Carefully characterizing what’s known and what’s uncertain is crucial to managing the risks sea-level rise poses to coasts around the world,” Kopp says.

Scientists used case studies from Atlantic City, New Jersey, and from Singapore to discuss how current methods for reconstructing past sea-level change can constrain future global and local projections. They also discussed approaches for using scientific sea-level projections and how accurate projections can lead to new sea-level research questions.

A large portion of sea-level rise in the 20th century, including most of the global rise since 1975, is tied to human-caused global warming, the study says.

Additional coauthors are from Rutgers, Boston College, and Nanyang Technological University.