20th century sea-level rose fastest in 3,000 years: Study

Driven by man-made climate change, global sea level rose faster in the 20th century than in any of the 27 previous centuries, new research has found.

Without global warming, global sea level would have risen by less than half the observed 20th century increase and might even have fallen, the study said.

Instead, global sea level rose by about 14 centimetres from 1900 to 2000 - a substantial increase, especially for vulnerable, low-lying coastal areas.

"The 20th-century rise was extraordinary in the context of the last three millennia - and the rise over the last two decades has been even faster," said study lead author Robert Kopp, associate professor at Rutgers University in New Jersey, US.

The study, published in the journal Proceedings of the National Academy of Sciences, used a new statistical approach that the researchers developed over the last two and a half years.

Notably, the study found that global sea level declined by about eight centimetres from 1,000 A. D. to 1400 A. D., a period when the planet cooled by about 0.2 degrees Celsius.

"It is striking that we see this sea-level change associated with this slight global cooling," Kopp said.

By comparison, global average temperature today is about one degrees Celsius higher than it was in the late 19th century.

A statistical analysis can only be as good as the data it's built upon.

For this study, the researchers compiled a new database of geological sea-level indicators from marshes, coral atolls and archaeological sites that spanned the last 3,000 years.

The database included records from 24 locations around the world. The analysis also tapped 66 tide-gauge records from the last 300 years.

The study also found that it is very likely that global sea level will rise by 1.7 feet to 4.3 feet in the 21st century if the world continues to rely heavily upon fossil fuels.

Phasing out fossil fuels will reduce the very likely rise to between 0.8 feet and 2.0 feet, the study said.