Sea level variability in continuous records of the past 500,000 years, and implications for the future

Lecture by Prof. Eelco Rohling, Professor of Oceanography, National Oceanographic Centre SOES, Southampton University. 

Abstract lecture

Over the last decade, we have developed a new sea-level quantification tool. Results agree with those from existing methods (notably fossil corals), but new method for the first time allows continuous resolution in 100-200 year time-steps. This allows comparison of the history of sea level, and hence global ice volume, with variability in other key climate parameters, notably temperature and greenhouse-gas concentrations measured in ice-cores. Comparison between temperature and sea-level changes over the past half million years (= 5 full glacial cycles) reveals an exponential relationship. Used with the ice-core-derived temperature:CO2 relationship, this relationship implies that natural processes would drive sea level to a long-term (millennial-scale) equilibrium position at around 25±5 m above the present, for the current 387 ppmv CO2 concentration. This portrays the disequilibrium state in the climate system, or the total potential ice-volume adjustment that might be expected if the current CO2 concentrations were maintained over several millennia. Other results reveal that rises above the present sea level (during the Last Interglacial) progressed at rates up to 1.6±1.0 m per century. The total magnitude and rates of sea-level adjustment found from these natural data significantly exceed model-based IPCC projections, even when considering their scenarios with 'high climate sensitivity'. Time permitting, I will go into our most recent work, which begins to reconcile the apparent discrepancy, by revealing potential non-linear behaviour of climate sensitivity and/or the polar temperature response to climate forcing.

Date of lecture: 25 January 2010

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