20th century sea level rose at fastest rate since founding of Rome

Sea levels rose faster last century than during any time since Rome was founded around 2,800 years ago. Reconstructing past rises and falls in global sea level, researchers estimate that more than half of the 13.8 centimeters of sea level rise recorded in the 1900s resulted from global warming effects, such as glacial melt. The new work will appear in the Proceedings of the National Academy of Sciences.

The researchers, led by climate scientist Robert Kopp of Rutgers University in Piscataway, N.J., analyzed measurements of ancient sea levels collected from 24 locations around the world, from New Zealand to New Jersey. The researchers calibrated the data using modern ocean tide measurements. They found that sea levels rose by about 0.1 millimeters per year from the first through the eighth centuries and fell around 0.2 millimeters per year during the 11th through 14th centuries. Sea levels rose abruptly around the start of the industrial revolution, with about 1.4 millimeters of sea level rise per year in the 20th century.

Simulating sea level in the absence of global warming, the researchers estimate that the 20th century rise would have been at most 0.7 millimeters annually. Rising sea levels worsen coastal flooding and threaten island nations.