Rising seas will severely test humanity's resilience in the second half of the 21st century and beyond, even if nations defy the odds and cap global warming at the ambitious 1.5 degrees Celsius target, researchers said Tuesday.

The pace at which global oceans are rising has doubled in three decades, and on current trends will double again by 2100 to about one centimetre per year, they reported in a study.

"Limiting global warming to 1.5C would be a major achievement" and avoid many dire climate impacts, lead author Chris Stokes, a professor at Durham University in England, told AFP.

"But even if this target is met," he added, "sea level rise is likely to accelerate to rates that are very difficult to adapt to."

Absent protective measures such as sea walls, an additional 20 centimetres (7.8 inches) of sea level rise -- the width of a letter-size sheet of paper -- by 2050 would cause some $1 trillion in flood damage annually in the world's 136 largest coastal cities, earlier research has shown.

Some 230 million people live on land within one metre (3.2 feet) of sea level, and more than a........

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