[Catalyst 2018]

HIGH-ALTITUDE SULFUR INJECTION
by Meredith Brown
I
f global warming increases the temperature
of the Earth by more than two degrees
Celsius, there will be catastrophic
consequences - major flooding will wipe out
homes, businesses, and ecosystems. 1 Sulfur
dioxide may hold the answer to combating the
threat of global warming. Although aerosols
and sulfur dioxide are detrimental to the
ozone layer and human health, studies have
shown that sulfur dioxide increases both plant
growth and the overall reflectivity of solar
radiation of the Earth’s atmosphere, known as
the Earth’s albedo. 2 Scientists hypothesize that
by injecting sulfur dioxide into the atmosphere,
we could combat the gradual temperature
increase without harming human and plant
life.
The negative consequences of aerosols
and sulfur dioxide are well documented.
Both are banned in large quantities by the
MARPOL regulations and by the National
Ambient Air Quality Standards enforced by
the Environmental Protection Agency.3 The
most harmful aerosols found in hairspray
cans and other products were made illegal in
the United States in the 1970s. 2 Additionally,
atmospheric sulfur dioxide precipitates as
acid rain, negatively affecting plants and
ecosystems. Furthermore, sulfur emissions
are responsible for a large percentage of
particulate matter, a class of air pollutants that
is responsible for approximately two million
deaths per year globally due to respiratory
problems. 4 Sulfur dioxide and aerosols also
play key roles in the destruction of the ozone
layer, the main component of the atmosphere
that protects humans from harmful UV rays. 3
In order to utilize sulfur dioxide to counteract
greenhouse gases, these negative impacts
must be mitigated.
Despite these numerous risks, aerosols
and sulfur dioxide have potential that
encourage scientists to look beyond their
negative qualities. Although sulfur dioxide is
a particulate matter pollutant, it also acts as a
cloud catalyst in certain layers of
the atmosphere.
In this
insane or insanely genius?
phenomenon, water vapor in the air is able
to cling to sulfur dioxide molecules more
easily than to salt crystals or to other water
molecules, resulting in a larger and brighter
cloud cover. This is desirable because larger
and brighter clouds reflect more solar
radiation than smaller and dimmer clouds that
lack sulfur. More solar radiation is reflected
back into space, and thus, less solar energy is
Water vapor in the air is able to
cling to sulfur dioxide molecules
more easily, causing clouds to be
larger, more frequent, and brighter.
available for greenhouse gases to trap near
the Earth’s surface. Also, sulfur dioxide plays a
critical role in plant growth. When a solar ray
cuts through Earth’s atmosphere, it generally
travels in a straight line. But if the ray hits the
large sulfur dioxide particles, the light scatters.
This scattered light is able to reach more plants
on the ground, allowing plants to grow larger.
Larger plants are desirable because the leaves
have a greater surface area and are thus able
to absorb more carbon dioxide, removing this
potent greenhouse gas from the atmosphere.
Dr. David Keith, a professor of physics and
public policy at Harvard University, has
outlined one cheap method of using sulfur
dioxide to combat global temperature
increases: high altitude injection. 3 He proposes
that specialized planes could fly annually and
inject one million tons of sulfur dioxide to
create a thin atmospheric layer intended to
reflect one percent of solar rays. These planes
would fly 20 kilometers high, beyond the cloud
formation point, to avoid contributing to acid
rain, while still reflecting solar radiation before
it ever hits Earth’s surface. Therefore, this
solar radiation is unable to become trapped
by greenhouse gases, thereby slowing Earth’s
temperature increase. In fact, this concept was
underscored by a mega-volcanic eruption in
1991, where a major increase in sulfur caused
a decrease in global temperature by half a
degree Celsius for two years. 5
However, this solution still has some
flaws. Scientists fear disruptions in
precipitation patterns,
reductions in
atmospheric ozone, and obstacles in logistics
regarding “who will inject the sulfur, where
will they inject the sulfur, and who will pay
for this?” Furthermore, the molecular size
of sulfur dioxide causes the particle to
have a short atmospheric life, so gas would
have to be continuously pumped into the
atmosphere, costing billions of dollars and
acting as a mere band-aid for our emissions
problems. 6 Scientists argue against this
tactic by suggesting that if the world were to
develop low-emissions energy systems and
transportation methods, such steps would fix
the greenhouse gas problem in a cheaper and
more sustainable manner in the long-run. Al
Gore denounced this geo-engineering plan,
calling it “insane, utterly mad and delusional in
the extreme.” 7
While high altitude sulfur dioxide injections
are possible with current technology, there
is not enough information to determine the
full scope of the environmental impact. Many
scientists have simply suggested decreasing
emissions to combat the source of the
problem instead of putting on the “bandaid”
of high-altitude sulfur dioxide injection.
However, most scientists can agree that
something must be done to mitigate our air
pollution problem, but global warming is a
challenge that we must tackle immediately.
WORKS CITED
[1] Aton, ClimateWire Adam. “Earth Almost Certain to Warm
by 2 Degrees Celsius.” Scientific American, 1 Aug. 2017, www.
scientificamerican.com/article/earth-almost-certain-to-warmby-2-degrees-celsius/.
[2] “Sulfur Dioxide: Its Role in Climate Change.” Institute for
Global Environmental Strategies >> Sulfur Dioxide: Its Role
in Climate Change, esseacourses.strategies.org/module.
php?module_id=168.
[3] “Setting and Reviewing Standards to Control SO2
Pollution.” EPA, Environmental Protection Agency, 13 Oct.
2017, www.epa.gov/so2-pollution/setting-and-reviewingstandards-control-so2-pollution#standards.
[4] Physics, Institute of. Researchers Estimate over Two Million
Deaths Annually from Air Pollution, www.iop.org/news/13/jul/
page_60518.html.
[5] Rotman, D. A Cheap and Easy Plan to Stop Global Warming
. MIT Technology Review. https://www.technologyreview.
com/s/511016/a-cheap-and-easy-plan-to-stop-global-warming/
(accessed Nov 7, 2017).
[6] Stephen et al. Self, pubs.usgs.gov/pinatubo/self/.
[7] Hansman, Heather. “Is This Plan to Combat Climate
Change Insane or Insanely Genius?”Smithsonian.com,
Smithsonian Institution, 14 May 2015, www.smithsonianmag.
com/innovation/is-this-plan-combat-climate-change-insaneinsanely-genius-180955258/.
DESIGN BY Katrina Cherk
EDITED BY Anna Croyle
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CATALYST | 9