Ancient ice reveals scores of gigantic volcanic eruptions

Date:
March 16, 2022
Source:
University of Copenhagen - Faculty of Science
Summary:
Ice cores drilled in Antarctica and Greenland have revealed gigantic
volcanic eruptions during the last ice age. Sixty-nine of these
were larger than any eruption in modern history. According to the
physicists behind the research, these eruptions can teach us about
our planet's sensitivity to climate change.



FULL STORY ==========================================================================
Ice cores drilled in Antarctica and Greenland have revealed gigantic
volcanic eruptions during the last ice age. Sixty-nine of these were
larger than any eruption in modern history. According to the University
of Copenhagen physicists behind the research, these eruptions can teach
us about our planet's sensitivity to climate change.


==========================================================================
For many people, the mention of a volcanic eruption conjures up doomsday scenarios that include deafening explosions, dark ash billowing into the stratosphere and gloopy lava burying everything in its path as panicked
humans run for their lives. While such an eruption could theoretically
happen tomorrow, we have had to make do with disaster films and books
when it comes to truly massive volcanic eruptions in the modern era.

"We haven't experienced any of history's largest volcanic eruptions. We
can see that now. Eyjafjellajo"kull, which paralysed European air traffic
in 2010, pales in comparison to the eruptions we identified further back
in time. Many of these were larger than any eruption over the last 2,500 years," says Associate Professor Anders Svensson of the University of Copenhagen's Niels Bohr Institute.

By comparing ice cores drilled in Antarctica and Greenland, he and his
fellow researchers managed to estimate the quantity and intensity of
volcanic eruptions over the last 60,000 years. Estimates of volcanic
eruptions more than 2,500 years ago have been associated with great
uncertainty and a lack of precision, until now.

Sixty-nine eruptions larger than Mount Tambora Eighty-five of the
volcanic eruptions identified by the researchers were large global
eruptions. Sixty-nine of these are estimated to be larger than the
1815 eruption of Mount Tambora in Indonesia -- the largest volcanic
eruption in recorded human history. So much sulfuric acid was ejected
into the stratosphere by the Tambora eruption that it blocked sunlight
and caused global cooling in the years that followed. The eruption also
caused tsunamis, drought, famine and at least 80,000 deaths.



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"To reconstruct ancient volcanic eruptions, ice cores offer a few
advantages over other methods. Whenever a really large eruption occurs, sulfuric acid is ejected into the upper atmosphere, which is then
distributed globally - - including onto Greenland and Antarctica. We can estimate the size of an eruption by looking at the amount of sulfuric
acid that has fallen," explains Anders Svensson.

In a previous study, the researchers managed to synchronize ice cores
from Antarctica and Greenland -- i.e., to date the respective core layers
on the same time scale. By doing so, they were able to compare sulphur
residues in ice and deduce when sulfuric acid spread to both poles after globally significant eruptions.

When will it happen again? "The new 60,000-year timeline of volcanic
eruptions supplies us with better statistics than ever before. Now we
can see that many more of these great eruptions occurred during the
prehistoric Ice Age than in modern times. Because large eruptions are relatively rare, a long timeline is needed to know when they occur. That
is what we now have," says Anders Svensson.

One may be left wondering when the next of these massive eruptions
will occur.

But Svensson isn't ready to make any concrete predictions: "Three
eruptions of the largest known category occurred during the entire period
we studied, so-called VEI-8 eruptions (see fact box). So, we can expect
more at some point, but we just don't know if that will be in a hundred
or a few thousand years. Tambora sized eruptions appears to erupt once
or twice every thousand years, so the wait for that may be shorter."


==========================================================================
How was climate affected? When powerful enough, volcanic eruptions can
affect global climate, where there is typically a 5-10- year period of
cooling. As such, there is great interest in mapping the major eruptions
of the past -- as they can help us look into the future.

"Ice cores contain information about temperatures before and after the eruptions, which allows us to calculate the effect on climate. As large eruptions tell us a lot about how sensitive our planet is to changes
in the climate system, they can be useful for climate predictions,"
explains Anders Svensson.

Determining Earth's climate sensitivity is an Achilles heel of current
climate models. Svensson concludes: "The current IPCC models do not
have a firm grasp of climate sensitivity - - i.e., what the effect of
a doubling of CO2 in the atmosphere will be.

Vulcanism can supply us with answers as to how much temperature changes
when Earths atmospheric radiation budget changes, whether due to CO2 or a blanket of sulphur particles. So, when we have estimated the effects of
large volcanic eruptions on climate, we will be able to use the result
to improve climate models."

========================================================================== Story Source: Materials provided by University_of_Copenhagen_-_Faculty_of_Science. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Jiamei Lin, Anders Svensson, Christine S. Hvidberg, Johannes
Lohmann,
Steffen Kristiansen, Dorthe Dahl-Jensen, Jo/rgen Peder Steffensen,
Sune Olander Rasmussen, Eliza Cook, Helle Astrid Kjaer, Bo
M. Vinther, Hubertus Fischer, Thomas Stocker, Michael Sigl, Matthias
Bigler, Mirko Severi, Rita Traversi, Robert Mulvaney. Magnitude,
frequency and climate forcing of global volcanism during the
last glacial period as seen in Greenland and Antarctic ice cores
(60-9 ka). Climate of the Past, 2022; 18 (3): 485 DOI:
10.5194/cp-18-485-2022 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220316115000.htm

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