Volcanic eruptions and climate change!
A volcanic eruption occurs when hot
materials like lava, rocks, dust ash and
gas escape from the earth’s crust through
vents to the lithosphere. Some derisively
refer to volcanic eruptions as Mother
Nature’s way of farting! Due to the
seriousness of the matter, the effects of
climate change on the environment have
been analyzed over the last two
DrillBytes’ columns. In a report
conducted by a team of geophysicists of
the University of Geneva and released 31
August, 2015 (Estimates of volcanic-
induced cooling in the Northern
Hemisphere over the last 1,500 years),
the analysis of the impact of volcanic
eruptions over the climate was eruditely
explained. This impact, which is the
focus of the column this week, concludes
DrillBytes’ trilogy on climate change.
Large volcanic eruptions inject
considerable amounts of sulphure in the
stratosphere which, once converted into
aerosols, block sun rays and tend to cool
the surface of the earth down for several
years. An international team of
researchers has just developed a method,
published in Nature Geoscience, to
accurately measure and simulate the
induced drop in temperature. Considered
the most important volcanic event of the
20th century, the eruption of Mount
Pinatubo (June 1991) injected 29 million
tons of sulphure dioxide in the
stratosphere and provoked a global
cooling of 0.40C on average.
To quantify the temporary cooling
induced by the largest eruptions over the
last 1,500 years, whose magnitude
exceeded Mount Pinatubo’s, scientists
usually adopt two approaches:
Dendroclimatology which relies on the
analysis of tree-ring based proxies and
climate model simulations in response to
the volcanic particles effect. But until
now, these two approaches delivered
results that were quite contradictory,
and this prevented scientist from
accurately assessing the impact of major
volcanic eruptions on climate.
Simulations showed greater (between
two and four times higher) and longer
cooling than dendroclimatic
reconstructions. This gap even led some
geophysicists to doubt the capacity of
tree-ring based proxies to measure the
impact of past major volcanic events in
climate and to question the models’
ability in simulating precisely the
climate response to strong volcanic
impacts.
Reconstruction of observational proxy
and model evidence Today, researchers
from the University of Geneva (UNIGE),
Switzerland, the Institut Pierre Simon
Laplace, IRD, the French Alternative
Energy Commission (CEA) and the
national center for scientific research
(CNRS), France have managed to
reconcile the two approaches and
developed a method to evaluate
accurately the consequence of future
high-magnitude eruptions on climate to
better anticipate their impact on our
societies.
In this multi-disciplinary team,
dendrochronologists came up with a new
reconstruction of the Northern
Hemisphere summer temperature in the
last 1,500 years. This reconstruction is
mainly based on maximum latewood
density, a parameter which is very
sensitive to temperature variations. Data
has been collected throughout the
Northern Hemisphere from Scandinavia
and Siberia all the way to Quebec,
including Alaska, the Alps and the
Pyrenees. The inclusion of density
allowed clear detection of all major
eruptions. Results show that the year
following a large eruption is
characterized by a greater cooling than
asserted in previous reconstructions and
that this cooling does not last for more
than three years at an hemispheric scale.
In parallel, using a sophisticated climate
model, climate physicists calculated the
drop in temperature caused by the two
largest volcanic events of the last
millennium, the Samalas and Tambora
eruptions which occurred in Indonesia
in the years 1257 and 1815. This model
combines data about location of
volcanoes, the period of eruption, the
amount of sulphure dioxide injected, and
integration of results from a
microphysical model which simulates the
volcanic aerosol life cycle from their
formation, following the oxidation of
sulphure dioxide, to their sedimentation
and elimination from the atmosphere.
“This unusual approach enables us to
realistically simulate the size of the
volcanic aerosols particles and hence,
their life expectancy in the atmosphere
which directly influences both the extent
and persistence of the cooling induced
by an eruption”, explains Markus Stoffel,
a researcher at UNIGE. These new
simulations show that disruptions in ray
exchange, caused by volcanic activity,
were largely overestimated in previous
climate simulations, used in the latest
Inter-governmental Panel on Climate
Change, IPCC report.
For the first time, results provided by
reconstructions and climate models
about the intensity of cooling converge
and demonstrate that the Tampora and
Samaras eruptions generated an average
drop in temperature in the Northern
Hemisphere fluctuating between 0.80C
and 1.30C during the summer of year
1258 and year 1816. Both approaches
also agree on the average persistence of
the significant cooling which is
estimated at two years to three years.
These results pave the way to a better
assessment of the role played by
volcanism on climate change.
It is clear from the erudite submission
that volcanic eruptions have a direct
bearing on the temperature of the
immediate environment which translates
to changes in climatic conditions over
time. Understanding our habitat to
manage its challenges is the focus of the
research.
•Kayode Adeoye is an oil and gas expert.
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