Magnitude, Rates and Sources of Sea-level Rise Associated with Past Polar Ice-sheet Retreat
Abstract:Over the past 3 million years, several intervals of warmth were associated with higher sea levels that were driven, in part, by polar ice-sheet retreat in Greenland and/or Antarctica. These include interglacials during the Pliocene, Marine Isotope Stage (MIS) 11 and MIS 5e. These sea-level benchmarks of ice-sheet retreat during periods when global mean climate was ~1 to 3 °C warmer than pre-industrial and where atmospheric CO2 was ~100 ppm lower or similar to today are useful for understanding the potential for future sea-level rise. Observations from these previous warm periods demonstrate geographic variability in relative sea-level reconstructions due to the influence of several geophysical processes that operate across a range of magnitudes and timescales, and are at various stages of being reconciled through modeling of GIA, dynamic topography, and ice-sheet observations and reconstructions.
Despite existing uncertainties regarding the magnitude and timing of sea-level change, which generally magnify in amplitude farther into the past, it is clear that polar ice sheets are sensitive to modestly higher temperatures even at times of similar or weaker CO2 forcing relative to pre-industrial conditions. Robust estimates of the rates of sea-level rise associated with polar ice-sheet retreat and/or collapse remain a weakness in existing sea-level reconstructions, despite growing confidence regarding the absolute magnitude of peak sea levels during these past periods of warmth. In several cases, polar ice-sheet retreat is inferred from the total sea-level budget but identification of the specific ice-sheet sources (e.g., Greenland, West Antarctica, Wilkes Land) that are most susceptible to decay is hindered by very limited near-field evidence. Improving our understanding of the rates and sources of past sea-level rise will enhance our ability to provide more robust projections of regional patterns of sea-level and ice-sheet change in the future.