[Coral-List] Subject: Sea Level rise

Purkis, Sam spurkis at rsmas.miami.edu
Sat Mar 5 17:50:19 UTC 2022

To answer Gene's question about what pushed temperature (and sea level) so high 125,000 years ago (a period appended the moniker MIS-5e), I believe that our current understanding pins this to an astronomical forcing, namely Earth's obliquity (axial tilt) at that time. Such a 'hot' climate configuration is often termed a "Super-interglacial" and MIS-11 was similarly toasty (~400,000 yrs. ago). Earth's tilt controls insolation, and in both of these time periods, summer insolation in the northern hemisphere was sufficient to cause substantial loss of Greenland ice, thereby raising sea level up to 6 m higher than present. Greenland might even have been ice free at these times. It is important to keep in mind that Earth's obliquity during MIS-5e and -11 might have only increased the length of northern-hemisphere summer by a couple of days, reduced the length of winter by the same amount, but that was sufficient to set Greenland on a melting trajectory, at least for a few thousand years, until Earth's tilt became conducive for the next glacial periods to take hold. Such is the fine balance of ice on our planet and the danger of forcing the climate by increasing the atmospheric concentration of carbon dioxide anthropogenically. Steady as you go. Beyond a certain threshold, even Earth's obliquity cannot put the brakes on warming.
Finally, yes, the fact that CO2 peaked sometime after the initiation of ice melt 125,000 years ago is surely a function of the Earth system responding to astronomically-forced heating of the planet. A positive feedback.
Best wishes to all,

Dr. Sam Purkis
Professor and Department Chair
Department of Marine Geosciences
Rosenstiel School of Marine and Atmospheric Science (RSMAS)
University of Miami - The U
4600 Rickenbacker Causeway
Miami, Fl. 33149, USA

+1-305-421-4351 (office)
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Office N361, Lab N374 - N. Grosvenor
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