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New paper finds sea levels rose naturally to 29 feet higher than the present during last interglacial — Published in Nature Geoscience


New paper finds sea levels rose naturally to 29 feet higher than the present during last interglacial

A new paper published in Nature Geoscience finds “sea level rose to about 9 meters [29.5 feet] above the present at the end of the last interglacial.” The authors observe fossil coral reefs in Western Australia located 9.5 meters [31 feet] above the present sea level. Prior research has demonstrated Greenland temperatures were 8C higher than the present during the last interglacial. Obviously, this dramatic climate change was entirely driven by natural variability while CO2 remained “safe.” By comparison, the warming periods of the current interglacial, including the current warm period, are entirely within natural variability, not unprecedented, and not unusual. Furthermore, there is no evidence of a runaway greenhouse effect or runaway positive-feedbacks despite a climate that was naturally much warmer during the last interglacial.

Top two lines show sea levels during the last interglacial were about 9 meters higher than the present [bottom 4 lines]

Ice sheet collapse following a prolonged period of stable sea level during the last interglacial

Michael J. O’Leary, Paul J. Hearty, William G. Thompson, Maureen E. Raymo, Jerry X. Mitrovica & Jody M. Webster

Nature Geoscience (2013) doi:10.1038/ngeo1890

Published online 28 July 2013Abstract: During the last interglacial period, 127–116 kyr ago, global mean sea level reached a peak of 5–9 m above present-day sea level. However, the exact timing and magnitude of ice sheet collapse that contributed to the sea-level highstand is unclear. Here we explore this timing using stratigraphic and geomorphic mapping and uranium-series geochronology of fossil coral reefs and geophysical modelling of sea-level records from Western Australia. We show that between 127 and 119 kyr ago, eustatic sea level remained relatively stable at about 3–4 m above present sea level. However, stratigraphically younger fossil corals with U-series ages of 118.1±1.4 kyr are observed at elevations of up to 9.5 m above present mean sea level. Accounting for glacial isostatic adjustment and localized tectonics, we conclude that eustatic sea level rose to about 9 m above present at the end of the last interglacial. We suggest that in the last few thousand years of the interglacial, a critical ice sheet stability threshold was crossed, resulting in the catastrophic collapse of polar ice sheets and substantial sea-level rise.

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