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Methane
A Powerful Greenhouse Gas
By Frederic Beaudry
Methane
is a major constituent of natural gas, but its chemical and physical
characteristics also make it a powerful greenhouse gas and worrisome
contributor to global climate change.
Methane
A methane
molecule, CH4, is made of a central carbon atom surrounded by four hydrogens.
Methane
is a colorless gas usually formed in one of two ways:
Biogenic
methane is produced by microorganisms breaking down certain types of sugars in
conditions where oxygen is absent.
This
biologically-produced methane can be released to the atmosphere immediately
upon being produced, or it can be accumulated in wet sediment only to be
released later.
Thermogenic
methane was formed when organic matter was buried deeply under geological
layers and over millions of years, and then broken down by pressure and high
temperatures.
This type
of methane is the primary constituent of natural gas, making up 70 to 90% of
it. Propane is a common by-product found in natural gas.
Biogenic
and thermogenic methane may have different origins but they have the same
properties, making them both effective greenhouse gases.
Methane
as a Greenhouse Gas
Methane,
along with carbon dioxide and other molecules, contributes significantly to the
greenhouse effect.
Reflected
energy from the sun in the form of longer-wavelength infrared radiation excites
methane molecules instead of traveling out into space.
This
warms up the atmosphere, enough that methane contributes to about 20% of the
warming due to greenhouse gases, second in importance behind carbon dioxide.
Due to
the chemical bonds within its molecule methane is much more efficient at
absorbing heat than carbon dioxide (as much as 86 times more), making it a very
potent greenhouse gas.
Fortunately,
methane can only last about 10 to 12 years in the atmosphere before it gets
oxidized and turns into water and carbon dioxide.
Carbon
dioxide lasts for centuries.
An Upward
Trend
According
to the Environmental Protection Agency (EPA), the amount of methane in the
atmosphere has multiplied since the industrial revolution, growing from an estimated
722 parts per billion (ppb) in 1750 to 1834 ppb in 2015.
Emissions
from many developed parts of the world have now appeared to have leveled off,
however.
Fossil
Fuels Once Again to Blame
In the
United States, methane emissions come primarily from the fossil fuel industry.
Methane
is not released when we burn fossil fuels, as carbon dioxide does, but rather
during the extraction, processing, and distribution of fossil fuels.
Methane
leaks out of natural gas wellheads, at processing plants, out of faulty
pipeline valves, and even in the distribution network bringing natural gas to
homes and businesses.
Once
there, methane continues to leak out of gas meters and gas-powered appliances
like heaters and stoves.
Some
accidents occur during the handling of natural gas resulting in the release of
large amounts of gas.
In 2015
very high volumes of methane were released from a storage facility in
California.
The
Porter Ranch leak lasted for months, emitting almost 100,000 tons of methane
into the atmosphere.
Agriculture:
Worse Than Fossil Fuels?
The
second-largest source of methane emissions in the United States is agriculture.
When
evaluated globally, agricultural activities actually rank first.
Remember
those microorganisms that produce biogenic methane in conditions where oxygen
is lacking? Herbivorous livestock guts are full of them.
Cows,
sheep, goats, even camels have methanogenic bacteria in their stomach to help
digest plant material, which means they collectively pass very large quantities
of methane gas.
And it is
not a minor issue, as a full 22% of methane emissions in the United States are
estimated to come from livestock.
Another
agricultural source of methane is the production of rice.
Rice
paddies contain methane-producing microorganisms as well, and the soggy fields
release about 1.5% of global methane emissions.
As the
human population grows and with it the need to grow food, and as temperatures
rise with climate change, it is expected that methane emissions from rice
fields will continue to increase.
Adjusting
rice-growing practices can help alleviate the problem: temporarily drawing down
water mid-season, for example, makes a big difference but for many farmers, the
local irrigation network cannot accommodate the change.
From
Waste to Greenhouse Gas
Organic
matter decomposing deep inside a landfill produces methane, which is normally
vented out and released into the atmosphere.
It’s an
important enough problem that landfills are the third-largest source of methane
emissions in the United States, according to the EPA.
Fortunately,
an increasing number of facilities capture the gas and route it to a plant that
uses a boiler to produce electricity with that waste gas.
Methane
Coming From the Cold
As Arctic
regions warm up quickly methane is released even in the absence of direct human
activity.
The
Arctic tundra, along with its numerous wetlands and lakes, contains large
amounts of peat-like dead vegetation locked in ice and permafrost.
As those
layers of peat thaw, microorganism activity picks up and methane is released.
In a
troublesome feedback loop the more methane there is in the atmosphere, the
warmer it gets, and more methane is released from the thawing permafrost.
To add to
the uncertainty, another worrying phenomenon has the potential to further disrupt
our climates very rapidly.
Under
Arctic soils and deep in oceans large concentrations of methane exist entrapped
in an ice-like mesh made of water.
The
resulting structure is called a clathrate, or methane hydrate.
Large
deposits of clathrate can be destabilized by changing currents, underwater
landslides, earthquakes, and warming temperatures.
The
sudden collapse of large methane clathrate deposits, for whatever reason, would
release lots of methane into the atmosphere and cause rapid warming.
Reducing
Our Methane Emissions
As a
consumer, the most effective way to lower methane emissions is by reducing our
fossil fuel energy needs.
Additional
efforts include choosing a diet low in red meat to reduce the demand for methane-producing
cattle and composting to reduce the amount of organic waste sent to landfills
where it would produce methane.
Frederic Beaudry, Ph.D.
Professor of Environmental Science
Education
Ph.D., Wildlife Ecology, University of Maine
M.A., Natural Resources, Humboldt State
University
B.S., Biology, Université du Québec à
Rimouski
Introduction
Associate professor of environmental science,
Alfred University
Academic publication credits include
Biological Conservation and Journal of Applied Ecology
Experience
Frederic Beaudry, Ph.D., is a former writer
for ThoughtCo who contributed articles on pollution, global warming, and
climate science for three years. He is an associate professor of environmental
science at Alfred University in New York.
Prior to teaching, Dr. Beaudry worked as a
wildlife biologist, focusing on the ecology and conservation of birds and
turtles. He has authored several scientific papers on land use and conservation
and has conducted research examining land use changes and their effects on bird
and amphibian communities. Dr. Beaudry's work can be found in peer-reviewed
journals such as Biological Conservation, Journal of Applied Ecology, and the
Journal of Wildlife Management.
Education
Dr. Beaudry has a B.S. in biology from
Université du Québec à Rimouski and an M.A. in natural resources from Humboldt
State University. He earned a Ph.D. in wildlife ecology at the University of
Maine. He also completed postdoctoral research at the University of
Wisconsin-Madison.
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