The Sedimentary Record: Realistic Reference for Assessing Future Global Sea-Level Rise

Understanding global sea-level fluctuations at different time scales is highly relevant for our societies. One tenth of the world population, mostly urban, lives in coastal areas that lie 10 m or less above sea-level, representing only 2 per cent of the world's land area. In the last century, global (eustatic) sea-level has risen at rates averaging 1.7 ± 0.3 mm/yr, partially caused by human growth and related activities. Satellite observations show that these rates have increased since 1993 to reach 3.3±0.4 mm/yr. Although remote-sensing data suggest that ice sheets currently contribute little to sea-level rise, based on the most conservative estimates, global sea-level in 2100 could be at about 50 cm above today's level. However, ice sheet dynamic instabilities linked to climate warming may cause faster ice-mass loss. Some scientists warn that global rise by 2100 could be as high as 80 cm and perhaps significantly higher than 1 m.

The geological sedimentary record provides unique records to quantify the timing, amplitudes, rates, mechanisms/controls, and effects of eustatic sea level fluctuations. Based upon these sediment archives, one can demonstrate that higher rates of sea-level rise(2-4 m in a century) than the ones forecasted for the next century have occurred in the geological past and such rates are not uncommon. This information set realistic references for predicting future global sea-level changes. Studies of sedimentary sequences focusing on past intervals of climate warming, such as the last and penultimate deglaciations, and past time intervals warmer than today, such as interglacial Marine Isotope Stages (MIS-5e, MIS-11, MIS-31), the "mid" Pliocene warmth and the early Tortonian (earliest late Miocene) warm interval, the middle Miocene climate optimum, and the late Oligocene warmth, already provide a means to assess the eustatic sea level response of future climate trends.