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Greenhouse Gases – A Primer
1. What are Greenhouse Gases?
Greenhouse gases (GHG) are specific molecules in the air
that have the ability to trap heat in the Earth's
atmosphere. Most of these molecules, such as carbon
dioxide (CO2) and methane (CH4), occur naturally and have
historically helped to keep our planet temperate.
However, many human activities (e.g., the burning of
fossil fuels, the landfilling of waste, and the removal of
carbon sinks through deforestation) emit molecules of
CO2 and other greenhouse gases, increasing overall GHG
concentrations in the atmosphere and contributing to the
warming of the planet.
(https://www.wunderground.com/climate/co2.asp)
Greenhouse gases each have different attributes that affect climate change: some last longer in the
atmosphere, some are more abundant, and some are more efficient at trapping heat. For example,
methane is far less abundant in the atmosphere than carbon dioxide and has a shorter atmospheric
lifetime, but it is much more efficient at trapping heat, making it a more potent GHG.
2. How Do They Work?
As sunlight passes through the atmosphere to the earth’s surface, some of this solar energy is reflected
off of the surface back into the atmosphere. Greenhouse gases trap some of this reflected energy and
prevent it from escaping the earth’s atmosphere. The more greenhouse gases there are in the
atmosphere, the more of the sun’s heat they will trap; this results in a rise of the earth’s air and ocean
temperatures.
3. Three Factors Affect the Degree to Which Any Greenhouse Gas Will Influence Global
Warming:

Abundance in the Atmosphere: The concentration of a particular gas in the air – measured in
parts per million.

Atmospheric Lifetime: The length of time a certain gas stays in the atmosphere. Each gas can
remain in the atmosphere for different amounts of time – from a few years to several thousand
years.

Global Warming Potential: The potency of a gas. GWP is the measure of how strongly a gas
absorbs energy, per pound of emissions, relative to CO2. A gas with a higher GWP means it absorbs
more energy per pound and is therefore more effective at warming the earth.
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4. The Composition of the Earth’s Atmosphere
Earth’s atmosphere is comprised mainly of nitrogen, oxygen and water. Anthropogenic greenhouse
gases, i.e., caused by human activity, are actually a very small percentage.
a) Water Vapor concentrations in the atmosphere are not significantly impacted by any direct human
action but instead by the natural water cycle. Changes in atmospheric H2O concentrations are considered
to be a result of climate feedbacks related to the warming of the atmosphere, rather than a direct result
of humans.
b) Ozone emissions do not last very long and thus dissipate before reaching the stratosphere. As a result,
tropospheric ozone emissions play no significant role in exacerbating the greenhouse effect.
5. Which Gases Should We Really Care About?
Sourced from: http://science.kqed.org/quest/2014/12/12/what-are-greenhouse-gases-and-where-do-they-come-from/
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While carbon dioxide is a main greenhouse gas, it isn’t the only one. Long-lived GHGs (carbon dioxide
(CO2), methane (CH4), nitrous oxide (N2O)), and the fluorinated gases listed under the Kyoto Protocol
(sulfur hexafluoride (SF6), hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs)) are the main drivers
of climate change.
(Blasing, T.J. ad K. Smith 2011. "Recent Greenhouse Gas Concentrations." In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information
Analysis Center, Oak Ridge National Laboratory, US Department of Energy, Oak Ridge, TN, USA. http://cdiac.ornl.gov/pns/current_ghg.html)
6. What Are the Biggest Emission Sources?
AFOLU- Agriculture, Forest and Other Land Uses; http://www.ipcc.ch/report/ar5/wg3/
The energy, agricultural, and industrial sectors
account for roughly 80% of all global GHG
emissions.
World Resources Institute;
http://www.wri.org/blog/2014/11/6-graphs-explain-world’s-top-10-emitters
Emissions by country are similarly unbalanced.
From 1990 to 2011, the U.S., the E.U., China,
and the Russian Federation accounted for
slightly more than half of all global GHG
emissions.
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7. Breakdown of the Greenhouse Gases
1. Carbon dioxide (CO2) is the primary
greenhouse gas emitted by humans, mainly
through the combustion of fossil fuels
(responsible for 87% of all CO2 emissions). The
three types of fossil fuels that are used the most
are coal, oil, and natural gas. 43% of the carbon
dioxide emissions from fuel combustion are from
coal, 37% are from oil, and 20% are from natural
gas.1 The remainder is caused by the clearing of
forests and other land-use changes, as well as by
certain industrial processes such as cement
production, steel production, and glass
manufacturing.2
2. Methane levels have more than doubled over
the last 150 years, primarily from human actions
such as the production, transportation, and use
of fossil fuels; landfilling of waste; and intensive
livestock farming. U.S. methane emissions have
spiked 30% since 2002 – precisely the era when
fracking became mainstream.3 These activities
account for 64% of total methane emissions.4
The main natural sources of methane include:
wetlands, termites, and the oceans, all of which
account for 36% of methane emissions
worldwide. Methane lasts for only a couple of
decades compared to centuries for CO2, but it is
much more efficient at trapping heat (it has 86105 times the potency of carbon dioxide).
3. Nitrous Oxide (N2O) is more potent than both
carbon dioxide and methane. 62% of N2O
emissions come from natural sources, and 38%
from anthropogenic sources - mainly agriculture,
fossil fuel combustion, and industrial processes.5
Human activities have virtually doubled the
amount of reactive nitrogen compounds existing
in the environment since the beginning of
the industrial age.6 The vast majority of
manufactured nitrogen is used in agriculture as
fertilizer, but there are huge inefficiencies of
plant and animal nitrogen intake. Only about 1015% of reactive nitrogen enters a human mouth,
the rest is lost to the environment, cascading
through the Earth's soils, water ways, and into
the atmosphere.
Sources: see endnote 7
;
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4. Fluorinated Gases have virtually no natural
sources. These chemicals were developed and
introduced as a replacement for
chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) in order to abate
depletion of the stratospheric ozone layer. Fgases now have been discovered to be potent
greenhouse gases with long atmospheric
lifetimes and high GWPs. Due to F-gases’ high
GWPs and long atmospheric lifetimes relative to
other greenhouse gases, even small
atmospheric concentrations can have large
effects on global temperatures. They are
released into the atmosphere through leaks in,
servicing of, and disposal of equipment in which
they are used.
HUMAN SOURCES OF FLUORINATED GAS
PFC-14
5%
HFC-152a
20%
HFC-125
9%
PFC-116
1%
SF6
3%
HFC-134a
57%
HFC-23
5%
(http://ozone.unep.org/Assessment_Panels/SAP/Scientific_Assessment_2010/00SAP-2010-Assement-report.pdf)
There are four main categories of fluorinated gases--hydrofluorocarbons (HFCs),
perfluorocarbons (PFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3).

HFCs – The major emissions source of
these compounds is their use as
refrigerants (e.g., air conditioning
systems in vehicles and buildings). HFCs
are both the largest source of
fluorinated gas emissions and the
fastest growing source of greenhouse
gas emissions. Leakage of the
gases results in emissions during
manufacturing, maintenance, as well as
through regular usage and even
disposal.

SF6 – Sulfur hexafluoride is used as an
insulator and arc interrupter in electrical
transmission equipment, including
circuit breakers, as well magnesium
processing
and
semiconductor
manufacturing. The GWP of SF6 is
22,800, making it the most potent
greenhouse
gas
that
the
Intergovernmental Panel on Climate
Change has evaluated. Emissions occur
through leakage and maintenance
losses.

PFCs – PFCs are a significant source of
fluorinated gas emissions. These gases
are created during the production of
aluminum and semiconductors. PFC-14
(CF4) and PFC-116 (C2F6) account for the
majority of PFC emissions. The
aluminum industry produces 12,000
tons of CF4 and 900 tons of C2F6 annually,
making it the largest source of PFC
emissions.8

NF3 – Nitrogen trifluoride is primarily
produced in the manufacture of
semiconductors and LCD (Liquid Crystal
Display) panels, as well as certain types
of solar panels and chemical lasers. NF3
emission rates have increased 40-fold
between 1992 and 2007 alone. This is
particularly serious as NF3 is 17,200
times more effective than carbon
dioxide in trapping atmospheric heat
over a 100-year time span.
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8. GHG Emissions Are Still Increasing
Globally, emissions of the
Kyoto greenhouse gases
increased by 75% between
1970 and 2004 (CO2 by 90%,
CH4 by 40%, N20 by 50%) to
about 45,000 megaton CO2equivalents.9
The large amounts of GHG
emissions have affected
the planet’s atmospheric
composition. Between 1750
and 2010, atmospheric
concentrations of CO2
increased 40%, CH4 150%,
and N2O 20%.10 These levels
are unprecedented in at
least 800,000 years. This
increase was not a gradual
change – over half of the
cumulative anthropogenic CO2 emissions between 1750 and 2011 have occurred in the last 40 years, while
emissions were the highest in history from 2000 to 2010. 11
Fluorinated gas emissions have greatly increased in recent years – by 73% in the U.S. and 60% in the E.U.
since 1990.12 This growth largely has been driven by a 250% increase in emissions of hydrofluorocarbons
(HFCs). HFC emissions are projected to grow by nearly 140% from 2005 to 2020 as demands for
refrigeration continue to grow and as more ozone-depleting substances are replaced.13
(http://www.ipcc.ch/pdf/assessment-report/ar4/wg3/ar4-wg3-ts.pdf)
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9. What Impact Will Emissions Increases Have?
(http://i.telegraph.co.uk/multimedia/archive/01508/Climate-ChangeNEW_1508747a.jpg)
Rising atmospheric concentrations of GHGs will continue to heat the planet’s lower atmosphere. Some of
the detrimental effects of rising temperatures are highlighted below – for example, rising sea levels,
greater water insecurity, and damage of ecosystems. The global increase of GHG emissions will continue
to have serious impacts on the entire planet.
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Endnotes
1
CO2 Emissions from Fuel Combustions, International Energy Agency. CO2 Emissions from Fuel Combustion 2014,
https://www.iea.org/publications/freepublications/publication/CO2EmissionsFromFuelCombustionHighlights2014.
pdf
2
The Environmental Protection Agency, Draft Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2014,
February 2016, https://www3.epa.gov/climatechange/Downloads/ghgemissions/US-GHG-Inventory-2016-Chapter4-Industrial-Processes-and-Product-Use.pdf; The Global Carbon Budget 1959-2011, Le Quéré, C. et al., 2013,
http://www.earth-syst-sci-data.net/5/165/2013/essd-5-165-2013.pdf
3
McKibben, Bill, Global Warming’s Terrifying New Chemistry, The Nation, 2016,
http://www.thenation.com/article/global-warming-terrifying-new-chemistry/
4
Contribution of anthropogenic and natural sources to atmospheric methane variability, Nature, 2006,
http://www.nature.com/nature/journal/v443/n7110/abs/nature05132.html
5
Couplings Between Changes in the Climate System and Biogeochemistry, Intergovernmental Panel on Climate
Change, 2007, https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch7.html
6
Smith, Kevin A., Nitrous Oxide and Climate Change, 2010,
http://www.researchgate.net/publication/267337982_nitrous_oxide_emissions_from_the_nitrogen_cycle
7
http://www.earth-syst-sci-data.net/5/165/2013/essd-5-165-2013.pdf;
https://www.iea.org/publications/freepublications/publication/CO2EmissionsFromFuelCombustionHighlights2014.
pdf; http://www.nature.com/nature/journal/v443/n7110/full/nature05132.html;
https://www.ipcc.ch/pdf/assessment-report/ar5/syr/SYR_AR5_FINAL_full.pdf
8
Worton. David R., Atmospheric Trends and Radiative Forcings of CF4 and C2F6 Inferred From Firn Air, 2007,
http://www.researchgate.net/publication/6389386_Atmospheric_trends_and_radiative_forcings_of_CF4_and_C2
F6_inferred_from_firn_air
9
Global greenhouse gas emissions increased 75% since 1970, November 13, 2006,
http://www.pbl.nl/en/dossiers/Climatechange/TrendGHGemissions1990-2004
10
Climate Change Synthesis Report 2014, International Panel on Climate Change, 2015,
http://www.ipcc.ch/pdf/assessment-report/ar5/syr/SYR_AR5_FINAL_full.pdf
11
Ibid.
12
European Commissions, Climate Action, Fluorinated Greenhouse Gases, http://ec.europa.eu/clima/policies/fgas/index_en.htm
13
The Environmental Protection Agency, Overview of Greenhouse Gases,
https://www3.epa.gov/climatechange/ghgemissions/gases/fgases.html
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