The volcanos did it

Why did the glaciers below the equator retreat 17,700 years ago (17.7 ka)?  A series of volcanic eruptions spanning 192 years down there did it according to Proc. Natl. Acad. Sci. vol. 114 pp. 10035 – 10040 ’17.  No one was driving SUVs then and mankind had barely invented farming in the old world.   Have we had an usual amount of volcanic activity in the past 100 to 1,000 years? Here’s the summary.

“Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ∼17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts.

We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ∼192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to stratospheric ozone depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics—similar to those associated with modern stratospheric ozone depletion over Antarctica—plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ∼17.7 ka.”

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  • andyextance  On September 23, 2017 at 5:47 am

    Admittedly no SUVs, but the key factor was volcano release of CO2, and SUVs also definitely release CO2. Meanwhile, I’m pretty confident we can’t point to the same level of volcanic activity. Admittedly, it’s a bit complex as volcanoes also release sulfates that lead to short-term cooling, while the CO2 effect is longer-lasting. The IPCC wraps volcanic effects as part of the ‘natural radiative forcing’ that includes changes from the sun, and compares it with human radiative forcing here:

  • luysii  On September 23, 2017 at 8:57 am

    As I drove to the diner to eat breakfast this AM in my SUV, I passed a virtuous bicyclist going the same way. Undoubtedly he was emitting less CO2 than my SUV, but I do wonder about the excess CO2 he emitted due to the effort of bicycling as opposed to just sitting there at home.

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