When did modern rates of sea-level rise start?

Accelerations and inflexions in recent sea-level records are known from instrumental (tide-gauge) datasets, but such records are generally too short to shed light on the question when modern rapid rates of sea-level rise commenced. Proxy sea-level records should therefore also be considered. In this review we compare recent proxy and instrumental sea-level records from the North Atlantic, Australia and New Zealand with the long-term (linear) rate of relative sea-level change that prevailed in the centuries and millennia before the 19th century. We re-evaluate dating models that underpin many of the proxy records and only consider published sea-level index points for which a reliable age can be firmly established. For seven coastal sites we determine the start of recent rapid sea-level rise by identifying the time when sea-level rise first departed from the long-term background rate. We find that within a 40 year period, centred around 1925, sea-level rise in all sites started to exceed the late Holocene background rate. This is consistent with local tide-gauge records and also with global and regional tide-gauge compilations. We conclude that proxy and instrumental sea-level datasets record a similar 20th century inflexion. Possible mismatches identified in published literature are therefore reconciled. We suggest that northern hemisphere ice melt, primarily from the Greenland Ice Sheet and small Arctic glaciers, is the main driving mechanism of early 20th century sea-level rise.