Sea Level Rise Could Reach 50 Feet by 2300, Devastating Coastal Cities Globally

The global average sea level could rise nearly 50 feet by 2300 if greenhouse gas emissions remain high, according to a study published in the journal Annual Review of Environment and Resources.

An international team of scientists reviewed research on sea-level change in order to synthesize our current understanding of the topic and help make better projections for the future. In the paper, they summarize this understanding over the near, medium and long terms.

Sea level rise varies over location and time, and researchers have developed a range of methods to reconstruct past changes and project future ones. But despite the different approaches, the evidence from the reviewed studies reveals clear trends, although the uncertainty of future projections increases over time.

"Our review of the literature shows that central estimates of future sea level range from 0.2 to 0.3 meters [0.7-1 feet] by 2050; 0.4 to 1.5 meters by 2100; 0.6 to 4.1 meters by 2150; and 1.0 to 11.7 meters by 2300, with projections for high emissions scenarios reaching as high as 2.4 meters in 2100 and 15.5 meters in 2300," Robert Kopp, a professor in the department of Earth and planetary sciences at Rutgers University and an author of the study, told Newsweek.

A man stands in front of the skyline in Manila Bay, Philippines, on April 26, 2017. Metro Manila has been facing an increasing amount of flooding due to an overuse of groundwater causing the city to sink, as well as a rapid rise in sea levels that have been over double the global average. Jes Aznar/Getty Images

"Sea-level-rise projections are not very sensitive to emissions through 2050 but become increasingly sensitive thereafter," he said.

These increases are worrying considering that around 11 percent of the world's 7.6 billion people currently live in areas less than 33 feet above sea level. As a result, sea level rises pose a major risk to coastal populations, economies, infrastructure and ecosystems around the world, the authors argue.

Estimates of global average sea level rise over the 20th century are about 1.1 to 1.9 millimeters per year (roughly half a foot per century), while more recent estimates since the early 1990s are about twice as fast—2.6 to 3.2 millimeters per year.

"A large portion of the 20th century rise, including most global mean sea level rise over the last quarter of the 20th century, is tied to human-caused warming—by its influence on the warming ocean and shrinking land ice," Kopp said.

Carefully characterizing what's known and what's unknown regarding sea level rise is crucial to managing the risks that it poses to coastal and small island communities around the world, according to the authors.

The study also looked at two case studies of future sea level rise: New Jersey and Singapore.

"In both New Jersey and Singapore, sea level rise will accelerate," Benjamin Horton, another author of the study from Nanyang Technological University in Singapore, told Newsweek. "In both locations there is a clear difference between high and low emission scenariosand the big threat is the fate of the Antarctic ice sheet."

"Sea levels in New Jersey are very susceptible to a slow down of the Gulf Stream, whereas in Singapore we do not know what is happening to land level change," he said. "So therefore, each of these processes need to be studied on a regional level."

This article has been updated to include additional comments from Benjamin Horton.