A team of researchers led by Andrew Kemp of Yale University in Connecticut examined sediment cores taken from salt marshes in North Carolina. They used the remains of foraminifera – tiny protozoa that form a hard shell around themselves – to create an unbroken record of sea level going back two millennia. In order to ensure the validity of their approach, the researchers compared their reconstructions against tide-gauge measurements from North Carolina for the past 80 years and global tide-gauge records for the past 300 years.

The results, published in the Proceedings of the National Academy of Sciences, showed that sea level was relatively stable between 200 BC and 1000 AD, and then rose by about half a millimetre per year for 400 years during the warm period known as the Medieval Climate Anomaly. It then returned to relative stability until the late 19th century, when it began to rise by an average of more than two millimetres per year.

‘Scenarios of future rise are dependant on understanding the response of sea level to climate changes,’ Kemp said. ‘Accurate estimates of past sea-level variability provide a context for such projections.’

August 2011