Sea levels have risen more steeply during the past century than at any other time over the past 2,100 years, according to Benjamin Horton at the University of Pennsylvania in Philadelphia and his colleagues.

The researchers measured certain carbon, lead and caesium isotopes, and pollen residues in sediments from ten North Carolina salt marshes to reconstruct historical sea levels. The level was stable between 100 BC and AD 950, then rose by 0.6 millimetres a year until AD 1400. Because the climate then cooled, sea levels remained reasonably steady until the end of the nineteenth century. At this point, they began to climb by an average of 2.1 millimetres a year. Since then, the annual increase has, in some years, exceeded 2.5 millimetres — a response to climate warming, the authors say.

Proc. Natl Acad. Sci. USA doi:10.1073/pnas.1015619108 (2011)