The potential impacts of a sulfur- and halogen-rich supereruption such as Los Chocoyos on the atmosphere and climate
Authors: Brenna Hans , Kutterolf Steffen , Mills Michael J. , Krüger Kirstin 
Published: June 2020

Abstract. The supereruption of Los Chocoyos (14.6∘ N,
91.2∘ W) in Guatemala ∼84 kyr ago was one of the
largest volcanic events of the past 100 000 years. Recent petrologic data
show that the eruption released very large amounts of climate-relevant
sulfur and ozone-destroying chlorine and bromine gases (523±94 Mt
sulfur, 1200±156 Mt chlorine, and 2±0.46 Mt bromine). Using the
Earth system model (ESM) of the Community Earth System Model version 2 (CESM2) coupled with the Whole Atmosphere Community Climate Model version 6 (WACCM6), we simulated the impacts of the sulfur- and halogen-rich Los Chocoyos eruption on the preindustrial Earth system. Our simulations show that elevated sulfate burden and aerosol optical depth
(AOD) persists for 5 years in the model, while the volcanic halogens stay
elevated for nearly 15 years. As a consequence, the eruption leads to a
collapse of the ozone layer with global mean column ozone values dropping to
50 DU (80 % decrease) and leading to a 550 % increase in surface UV over the
first 5 years, with potential impacts on the biosphere. The volcanic
eruption shows an asymmetric-hemispheric response with enhanced aerosol,
ozone, UV, and climate signals over the Northern Hemisphere. Surface climate
is impacted globally due to peak AOD of >6, which leads to a maximum
surface cooling of >6 K, precipitation and terrestrial net
primary production decrease of >25 %, and sea ice area
increases of 40 % in the first 3 years. Locally, a wetting
(>100 %) and strong increase in net primary production (NPP) (>700 %)
over northern Africa is simulated in the first 5 years and related to a
southward shift of the Intertropical Convergence Zone (ITCZ) to the
southern tropics. The ocean responds with pronounced El Niño conditions
in the first 3 years that shift to the southern tropics and are coherent with the ITCZ change. Recovery to pre-eruption ozone levels and climate takes 15 years and 30 years, respectively. The long-lasting surface cooling is sustained by an immediate increase in the Arctic sea ice area, followed by a decrease in poleward ocean heat transport at 60∘ N which lasts up to 20 years. In contrast, when simulating Los Chocoyos conventionally by including sulfur
and neglecting halogens, we simulate a larger sulfate burden and AOD, more
pronounced surface climate changes, and an increase in column ozone.
By comparing our aerosol chemistry ESM results to other supereruption
simulations with aerosol climate models, we find a higher surface climate
impact per injected sulfur amount than previous studies for our different
sets of model experiments, since the CESM2(WACCM6) creates smaller aerosols with
a longer lifetime, partly due to the interactive aerosol chemistry. As the
model uncertainties for the climate response to supereruptions are very
large, observational evidence from paleo archives and a coordinated model
intercomparison would help to improve our understanding of the climate and
environment response.