Climate change will transform cooling effects of volcanic eruptions


Date:
August 12, 2021
Source:
University of Cambridge
Summary:
Researchers have shown that human-caused climate change will have
important consequences for how volcanic gases interact with the
atmosphere.



FULL STORY ========================================================================== Researchers have shown that human-caused climate change will have
important consequences for how volcanic gases interact with the
atmosphere.


==========================================================================
The researchers, from the University of Cambridge and the UK Met Office,
say that large-magnitude eruptions will have greater effects as the
climate continues to warm. However, the cooling effects of small-
and medium-sized eruptions could shrink by as much as 75%. Since these
smaller eruptions are far more frequent, further research is needed to determine whether the net effect will be additional warming or cooling.

Where and when a volcano erupts is not something that we can control,
but as the atmosphere warms due to climate change, the plumes of ash and
gas emitted by large, but infrequent, volcanic eruptions will rise ever
higher. Climate change will also accelerate the transport of volcanic
material -- in the form of small, shiny droplets called volcanic sulfate aerosols -- from the tropics to higher latitudes.

For large eruptions, the combined effect of these phenomena will cause
the haze created by volcanic aerosols to block more sunlight from
reaching Earth's surface, ultimately amplifying the temporary cooling
caused by volcanic eruptions. The results are reported in the journal
Nature Communications.

When Mount Pinatubo in the Philippines erupted in 1991, the effects
were felt worldwide. The plume from the eruption -- the second largest
of the 20th century -- reached more than 30 kilometres into the sky,
forming a layer of global haze. In 1992, this haze caused global
temperatures to drop by as much as 0.5 degrees Celsius. In comparison,
human activities have warmed global temperatures by over 1 degree Celsius
since 1850. However, the effect of volcanic aerosols only persists for
one or two years, while anthropogenic greenhouse gases will affect the
climate for centuries.

"Beyond the data we have from recent eruptions like Pinatubo, we can
also see the cooling effect of volcanoes going back two thousand years
from the information contained in tree rings," said Dr Thomas Aubry from Cambridge's Department of Geography, the paper's first author. "However,
we wanted to look at the question from the opposite angle: how could a
warming climate affect the cooling from volcanic eruptions?" Volcanic
plumes rise like hot air balloons: they keep rising to a height where
they're naturally buoyant. The Cambridge study looked at how high in
the atmosphere these plumes can rise and be transported globally under different warming scenarios.



==========================================================================
The researchers used global climate models combined with volcanic plume
models to simulate how the aerosols emitted by volcanic eruptions might
be affected by climate change.

They found that for large eruptions like Mount Pinatubo, which typically
occur once or twice per century, climate change will cause the plumes to
rise higher and the aerosols to spread faster over the globe, resulting
in a cooling effect amplified by 15%. Changes in ocean temperatures are expected to further amplify the cooling, and the melting of ice sheets
is also projected to increase volcanic eruptions frequency and size in
places such as Iceland.

However, for moderate-sized eruptions such as the 2011 Nabro eruption
in Eritrea, which typically occur on a yearly basis, the effect will be
reduced by about 75% under a high-end warming scenario. This is because
the height of the tropopause -- the boundary between the troposphere and
the stratosphere above it -- is predicted to increase, making it harder
for volcanic plumes to reach the stratosphere. Aerosols from volcanic
plumes confined to the troposphere are washed out by precipitation in
a matter of weeks, making their climatic impacts relatively minor and
much more localised.

"Climate change isn't something that's coming -- it's already here, as
clearly demonstrated by this week's IPCC report," said co-author Dr Anja Schmidt, also from the Department of Geography. "The effects of climate
change and some of the feedback loops it can cause are becoming more
obvious now. But the climate system is complex: getting a grasp of all
these feedback loops is critical to understanding our planet and making accurate climate projections." "The new feedback loops between climate
and volcanic eruptions that we highlight in this work are currently
unaccounted for by IPCC," said Aubry. "It could shed new light on the
evolution of future volcanic influences on climate.

Even if volcanoes have a limited influence on climate compared to human greenhouse gas emissions, they are an important part of the system."
"Due to more frequent and more intense wildfires, as well as other
extreme events, the composition of the upper atmosphere is changing
in front of our eyes, and so is our understanding of the consequences
of these changes," said Schmidt, who is also affiliated with the Yusuf
Hamied Department of Chemistry.

"As we continue to emit greenhouse gases, the way that volcanic emissions interact with the atmosphere will continue to change and it is important
to quantify these interactions in order to fully understand climate variability." The authors hope to bring together more volcanologists and climate scientists to understand not only the mechanics behind volcanic
plume rise and aerosol lifecycle, but also how changes in eruption
frequency and magnitude, driven by deglaciation and extreme precipitation,
will shape the future climatic effects of volcanic eruptions.

The research was funded by the Royal Society, the European Union's Horizon
2020 research and innovation programme, and the UK Natural Environment
Research Council.

========================================================================== Story Source: Materials provided by University_of_Cambridge. Original
written by Sarah Collins. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Thomas J. Aubry, John Staunton-Sykes, Lauren R. Marshall, Jim
Haywood,
Nathan Luke Abraham, Anja Schmidt. Climate change modulates the
stratospheric volcanic sulfate aerosol lifecycle and radiative
forcing from tropical eruptions. Nature Communications, 2021; 12
(1) DOI: 10.1038/s41467-021-24943-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210812082705.htm

--- up 13 weeks, 6 days, 22 hours, 45 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)