This document discusses the composition of the Earth's atmosphere and greenhouse gases. It notes that while nitrogen and oxygen make up most of the atmosphere, trace gases like water vapor, carbon dioxide, methane and nitrous oxide have an outsized influence on climate. These greenhouse gases absorb and emit thermal radiation and warm the atmosphere, comprising what is known as the greenhouse effect. The document also outlines the sources and sinks of various greenhouse gases as well as their impacts on climate change like rising global temperatures and sea levels.

2. Species Mixing ratio Source
Water Vapour 10,000 to 2 ppmv Natural
Methane 1.7 ppmv Biogenic
Nitrous oxide 310 ppbv Biogenic
Carbon monoxide 50-500 ppbv Anthropogenic
Ozone 10 ppbv to 10 ppmv Photochemical
Halocarbons Few hundred pptv Anthropogenic
COMPOSITION OF THE EARTH’S ATMOSPHERE
Major Gases
Trace Gases
Nitrogen
78.08%
Oxygen 20.03%
Others
Argon 0.93%

3. Gases which make up far less
than 1 percent of the atmosphere
have a much greater influence on
both short-term weather and long-
term climate.
The less abundant gases (H2O,
CO2, CH4, SO2, andN2O) all have
an important property.
These gases have the ability to
absorb thermal energy (heat)
emitted by the earth and thus are
able to warm the atmosphere. This
warming is what is popularly
called the "greenhouse effect.“

4. These gases are called greenhouse gases as without them the
surface of the earth would be about 30 degrees Celsius cooler,
and far too cold for life, as we know it, to exist. On the other
hand, these greenhouse gases are so thermally potent that
even proportionately small amounts can cause Earth’s lower
atmospheric temperature to rise.

5. Absorption of energy by greenhouse gases

6. Energy balance of the earth.

7. Radiation Balance

8. Primary Greenhouse Gases:
Gas
Water vapor (H2O) ~60
Carbon dioxide (CO2) ~26
Ozone (O3) ~8
Methane (CH 4)
Nitrous oxide (N2O ) ~6
Other
Greenhouse effect
contribution (%)

9. What causes it?
Human Impacts- Natural Impacts-

10. Global Greenhouse Gas Emissions by Gas, 1990–2005
In 2005, estimated worldwide emissions totaled nearly 39 billion
metric tons of greenhouse gases, expressed as carbon dioxide
equivalents. This represents a 26 percent increase from 1990.
. Emissions of carbon dioxide increased by 31 percent, which is
particularly important because carbon dioxide accounts for nearly
three-fourths of total global emissions. Methane emissions increased
the least—10 percent—while emissions of nitrous oxide increased by
14 percent. Emissions of fluorinated gases more than doubled.

11. Greenhouse Gas SOURCES SINK Importance for climate
Carbon Dioxide
• Burning of fossil fuel
• Land-use change
(deforestation)
•Ocean Uptake
•photosynthesis
Absorbs infrared
radiation; affects
stratospheric O3
Methane
•Biomass burning
•Enteric fermentation
•Rice paddies
• Reactions with OH
• Microorganisms
uptake by soils
Absorbs IR; affects
tropospheric &
stratospheric O3;
produces CO2
Nitrous Oxide
• Biomass burning
• Fossil-fuel combustion
• Fertilizers
• Removal by soils
• Stratospheric
photolysis and rxn
with O xygen
Absorbs IR; affects
stratospheric O3
Ozone •Photochemical
reactions involving O2
Catalytic chemical
reactions involving
NOx species.
Absorbs UV &
IR radiation
CFC Industrial production
dissociated in
stratosphere
Absorbs IR; affects
stratospheric O3
Sulphur dioxide Volcanoes, Coal and
Biomass burning
•Dry & wet deposition
•Reactions with OH
Forms aerosols, which
scatter solar radiation

12. Carbon is extensively recycled through the earth system,
including both the terrestrial, biosphere and the oceans.
CO2
CARBON CYCLE

13. Increased volcanism input huge quantities of CO2 into the
atmosphere resulting in the increase in temperature (T°)
The CO2 Cycle as Earth’s Thermostat
T° increase causes increased chemical weathering and marine
carbonate deposition which lowers atmospheric CO2

14. Future Carbon Dioxide Levels
 Increasing CO2 emissions, especially in China and developing
countries
 Likely to double within 150 years:
I. Increased coal usage
II. Increased natural gas usage
III. Decreased petroleum usage (increased cost and decreasing
supply)
Country Emission Per Capita
(Million Metric Tons/yr) (Metric Tons)
USA 1577 5.3
China 15100 1.16
Russia 410 2.87
India 383 (coal 70%, oil 21%) 0.35
Japan 336 2.63
Global Average 1.23

15. CH4
 Generally present in low concentration than CO2
 Atmospheric lifetime is important , of the long-lived greenhouse
gases (LLGHGs), methane has the shortest lifetime
(7 to 10 years) , being susceptible
to reaction with OH.
This figure shows concentrations of methane in
the atmosphere from hundreds of thousands of
years ago through 2011. The data come from a
variety of historical ice core studies and recent air
monitoring sites around the world. Each line
represents a different data source

16. N2O
 As a major source of NOx
in the stratosphere, where
it is transported due to long
tropospheric lifetime
(140 to 190 years)
 Sources: nitrification and
denirification in soils and
aquatic system, fertilizers etc This figure shows concentrations of nitrous
oxide in the atmosphere from 100,000
years ago through 2011. The data come
from a variety of historical ice core studies
and recent air monitoring sites around the
world. Each line represents a different data
source

17. O3
 Ozone is a triatomic form of oxygen (O2) found in Earth’s upper and
lower atmosphere.
 The ozone layer, situated in the stratosphere about 15 to 30 km above the
earth's surface.
 Ozone protects living organisms by absorbing harmful ultraviolet
radiation (UVB) from the sun.
 03 near the ground is at temperatures close to those of the earth's surface.
As a result, emission and absorption are occurring at essentially the
same temperature, resulting in no contribution to the greenhouse effect.
However, because the temperature falls with altitude up to the tropopause,
the Boltzmann distribution shifts to smaller relative populations in the
excited states. As a result, the net emission from 03 becomes smaller
relative to absorption.

18. 03 absorbs strongly in the UV as well, which leads to
heating in the stratosphere, in contrast to CO2, which
cools it. Thus, changes in the concentrations of ozone
and its vertical distribution affect not only infrared
but also solar UV radiation, with associated effects on
climate.

19. Estimated Global Warming Potential
Lifetime
20 years 100 years 500 yearsyears
GREENHOUSE GAS
Carbon Dioxide (CO2) Variable 1 1 1
Methane (CH4) 12 62 23 7
Nitrous Oxide (N2O) 114 275 296 156
CFCl3 (CFC11) variable 6300 4600 1600
CF2Cl2 (CFC12) variable 10200 10600 5200
Based on Intergovernmental Panel on Climate Change Third Assessment Report,
2001
GWP reflects the relative strength of individual greenhouse gas with
respect to its impact on global warming. It was defined as the
cumulative radiative forcing between the present and some future time
caused by a unit mass of greenhouse gas emitted now, expressed
relative to CO2.

20. Expected Consequences of increased GHG Concentration is:
Climate Change
GLOBAL WARMING
is the increase of the
Earth’s average surface
temperature due to a build-
up of greenhouse gases in
the atmosphere.
CLIMATE CHANGE
is a broader term that refers
to long-term changes in
climate, including average
temperature and
precipitation.

21. • The snow cover in the
Northern Hemisphere and
floating ice in the Arctic
Ocean have decreased
• Sea level has risen 4-8
inches over the past
century
• Global surface temp. could
rise 1-4.5°F (0.6-2.5°C) in
the next fifty years, and
2.2-10°F (1.4-5.8°C) in the
next century
Global mean surface temperatures have increased 0.5-1.0°F
since the late 19th century

22. Kyoto Protocol
• Framework
– stabilize greenhouse gas emissions to prevent anthropogenic
interference with the climate system
– emission targets for industrialized countries between 2008-
2012 are collectively about 5% lower than 1990 emissions
• US target is 7% reduction
• developing countries do not have quantified targets
– six gases
• CO2, CH4, N2O, HFCs, PFCs, SF6
"We must limit global temperature rise to 2 degrees. We are far from there,
and even that is enough to cause dire consequences. If we continue along the
current path, we are close to a 6 degree increase".
- UN Secretary-General Ban Ki-moon
Remarks at the Council on Foreign Relations (February 2013)

23. REFERENCES
 http://www.epa.gov/climatechange/pdfs/CI-greenhouse-gases-
2012.pdf
 Chemistry of upper and lower atmosphere-Barbara Pitts
 Class lecture slides
 http://www.rsc.org/images/CA1_tcm18-137981.pdf
 http://forecast.uchicago.edu/chapter4.pdf
 http://www.weather.gov.hk/prtver/pdf/docs/cis/climchange/grnh
se_e.pdf