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Chapter 3: Global Warming
What is global warming?
Can anything be done
about it?
Is there really cause
for alarm?
How can we assess
the information from
the popular press?
Greenhouse Effect
This is a naturally occurring process:
Energy from the sun heats up the earth's
surface
The earth is constantly losing energy by
emitting Infrared radiation (IR)
Greenhouse gases trap this energy and
keep the Earth warm
The Earth’s Energy Balance
Greenhouse
effect
Our atmospheric
gases trap and
return a major
portion of the
heat radiating
from the Earth.
It is a natural,
necessary
process.
3.1
The Sun's energy

Composed of IR, visible, UV, …

Only a small portion is directed at the Earth
About half of this is reflected or absorbed by
the upper atmosphere

Most of the rest is absorbed by the Earth
and turned into thermal energy

Thermal Energy
Thermal energy is a measure of how fast
atoms and molecules vibrate
As an object heats up, the atoms move
more quickly
All matter emits IR energy:
Warmer objects emit more IR energy
As IR is emitted, the object cools
(conservation of energy)

Some gases in the atmosphere are able to
absorb and re-emit this IR energy.
These gases trap ~80% of the energy given
off by the Earth.
This is the same effect as glass in a
greenhouse or in your car in the summer
Without these “greenhouse gases”, the Earth
would be 25 °C cooler (-10 °C average
versus the actual 15 °C average)

Some of the greenhouse gases are:
H2O vapor
CO
2
CH
4
N O
2
CFCs

According to data taken at Mauna Loa, Hawaii since 1958,
CO2 levels are on the rise.
3.2
Enhanced Greenhouse Effect




When more than 80% of the IR emitted
from the Earth is trapped
Due to increased greenhouse gases in the
upper troposphere
This increase in greenhouse gases is due
to human activities (anthropogenic)
Results in global warming
Anthropogenic sources of greenhouse gases
include:






Industry
Transportation
Mining
Agriculture
Energy (coal power plants)
Livestock
Global Warming


Due to the Enhanced Greenhouse Effect
An average increase in the temperature
over the entire surface of the earth

Determined by looking at years of data

Year to year average temps. may go up
or down, but the trend is increasing
History of average temperatures
 Only recently (last ~hundred years) is
accurate data directly available
 For previous years (up to 400,000 yrs ago),
ice core samples from the poles is used
• Average temperatures determined from:
– Trapped CO2 concentrations
– Hydrogen isotopes
– Microscopic plants and animals
• Some species are very sensitive to
small temperature changes
Microscopic air bubbles in ice core samples from glaciers can be
used to determine changes in greenhouse gas concentrations over
time.
3.2
Comparing ice core data from Antarctica and Mauna Loa
observations, the concentration of carbon dioxide appears to be
increasing over time.
3.2
The Vostok ice core shows data going back 400,000 years,
while other ice cores go back even further (the inset shows data
from the figure above). The current concentration of
atmospheric carbon dioxide is 100 ppm higher than any time in
the last million years.
3.2
Average global surface temperatures have increased since 1880.
The red bars indicate average temperatures for the year while the
black error bars show the range for each year. The blue line is
the 5-year moving average.
3.2
Global temperatures for 2006 (in oC) relative to the 1951–1980
average. The most dramatic changes have been observed in the
higher latitudes (dark red areas).
3.2
The concentration of carbon dioxide (blue) and the global
temperature (red) are well correlated over the past 400,000 years as
derived from ice core data.
3.2



Why are only some gases greenhouse
gases?
All molecules can emit infrared light as they
release thermal energy
But only certain molecules are able to
vibrate at the proper frequency to absorb IR
light (similar to ozone absorbing UV light)
These molecules then re-emit this IR

Some of this energy is lost in space

Most is trapped and redirected to the
Earth
Molecular geometry and absorption of IR radiation
Molecular vibrations in CO2. Each spring represents a C=O
bond.
(a) = no net change in dipole – no IR absorption.
(b, c, d) = see a net change in dipole (charge distribution), so
these account for IR absorption.
3.4
The infrared spectrum for CO2
As IR radiation
is absorbed,
the amount of
radiation that
makes it
through the
sample is
reduced.
3.4
Molecular response to different types of radiation
3.4
The Carbon Cycle
 The natural movement of carbon in the
environment
• Most carbon transported as CO2
• All living organisms are part of this cycle
– Carbon from many dead organisms is
absorbed back into cycle via
decay/decomposition
– Some carbon may be removed from the
cycle if isolated:
• entombed, fossilized, petrified,....
The carbon cycle
3.5

CO2 released from the Earth by

respiration: mainly animals, but plants
also release some CO2

natural burning

volcanoes

man-made activities

energy

combustion

cement production

accounts for 10% released
CO2 emission sources by end use:
3.5

CO2 absorbed by earth by:

plant respiration

absorb more than they release

this is reduced by deforestation

plants use CO2 and store energy
from the sun as saccharide
molecules (sugars)

Animals absorb some of this
carbon as food
Gases, including CO2, can dissolve in water,
though at low concentrations.
The oceans:
 release some CO due to animal respiration
2
 absorb much more CO than released
2

Most due to plant respiration

Some CO2 is trapped in pools at the
ocean floor due to very high pressures
Mass of Elements and Compounds

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

The mass of carbon is tracked through the
carbon cycle
Chemical reactions care about the number
of atoms/molecules, not mass
We cannot count the number of atoms in a
reaction (atoms too small: too many atoms)
We can measure mass and convert to
numbers


Atomic mass – Actual mass of an atom

slightly different than mass # due to
electrons and nuclear binding energy
Average atomic mass

Most elements in nature are composed
of multiple isotopes

The decimal value on the periodic table
gives the weighted average of these
isotopes in amu (atomic mass units)



If the atomic mass of an isotope is known,
then any mass of that isotope can be
converted to a number of atoms
If the average mass of an element is
known, then the number of atoms can also
be calculated
If the mass of a molecule is known, the we
can also calculate the number of molecules
in a sample from the mass


The Mole
The key to converting between mass and
numbers is the mole
'Mole' is just a number

1 mole (mol) = 6.022E23 (Avogadro's #)

We can have a mole of anything:

atoms

molecules

grains of sand....
To convert between moles and numbers:
Use the conversion factor:
1 mole = 6.022E23
For example:
1 mole atoms
1.204E24 atoms(
)= 2.000 moles atoms
6.022E23 atoms
6.022E23 atoms
2.50 moles atoms(
)= 1.506E24 atoms
1 mole atoms
6.022E23 molecules
1.5 mole molecules(
)= 9.03E23 molecules
1 mole molecules
6.022E23 H 2 O
1.5 mole H 2 O (
)= 9.03E23 H 2 O(molecules)
1 mole H 2 O
1 mole H 2 O
3.01E23 H 2 O (
)= 0.500 mole H 2 O
6.022E23 H 2 O

One mole of protons (or neutrons) has a
mass of one gram

(exactly one mole of C-12 atoms has a
mass of exactly 12 grams)

The decimal value on the PT (the
average atomic mass) may also be
used to convert mass to moles

This value gives the mass, in grams,
of one mole of the element
For example, to find the moles of hydrogen
atoms in 1.01 grams:
1 mole H
1.01 g H (
)= 1.00 mole H
1.01 g H
or for 12.5 grams of hydrogen atoms:
1 mole H
12.5 g H (
)= 12.4 mole H
1.01 g H
Or to find the mass of 2.5 moles of helium:
4.00 g He
2.5 moles He(
)= 10. g He
1 mole He
or for 2.5 moles of lead:
207.20 g Pb
2.5 moles Pb(
)= 518.0 g Pb
1 mole Pb
Note these two examples have the same
number of atoms, but different masses
Keep these relationships in mind:
grams
use
molar
mass
moles
use
Avogadro’s
number
molecules
Remember – the critical link between moles and
grams of a substance is the molar mass.
IT’S SIMPLE – THINK IN TERMS OF PARTICLES!
3.7


Formula Mass
The average mass of a compound
Calculated by adding up the atomic masses
of all of the atoms in one formula
For CO2:

1 carbon atom + 2 oxygen atoms

formula mass = 12.01 + 2(16.00)
= 44.01 amu

also: 1 mole CO2 = 44.01 g CO2
So, to find the mass of 1.5 moles of CO2:
44.01 g CO 2
1.5 moles CO 2 (
)= 66.02 g CO 2
1 mole CO 2
or to find the moles of 85.0 grams of CO2:
1 mole CO 2
85.0 g CO 2 (
)= 1.93 mole CO 2
44.01 g CO 2
Greenhouse Gases (GG)


Atmospheric lifetime

How long, on average, that a particular gas
molecule stays in the atmosphere

Ranges from tens to hundreds of years

So lowering production of a GG now may
take a century to see any effects
Global Warming Potential (GWP)

Relative effectiveness of how well a molecule
absorbs IR

GWP for carbon dioxide = 1



Significance of a GG on Global Warming
Mainly depends on three factors:

Concentration of the gas

Atmospheric lifetime of the gas

GWP of the gas
CO2 is considered the most significant gas

Relatively low GWP, but very high conc.
CFCs, for example, are not as significant

Larger GWP, but very low conc.
Global Warming Potential (GWP) represents the
relative contribution of a molecule of an
atmospheric gas to global warming.
3.8



Greenhouse Gases
CO2 – From combustion, deforestation (less
trees to absorb CO2), cement production
CH4 (methane) – From anaerobic bacteria
(live without molecular oxygen)

marshes, wetlands, rice paddies,
livestock
N2O – From fertilizers, industry, combustion


CFCs – from air conditioners, aerosols,
foams
H2O (water) – Also a product of combustion

Water has a large GWP and is present
in the atmosphere in high
concentrations

The environment usually controls water
vapor easily via evaporation and
precipitation (rain)

But a warmer climate can increase
water vapor levels, which will further
warm the Earth's surface

Reverse Global Warming?
Aerosols – Particulates suspended in the
air

May be solid or liquid

Can block sunlight from reaching the
Earth

Can cause global cooling

In the past, large volcanic eruptions
have resulted in significant global
cooling for a year or more

Resulted loss of crops, famine,
climate changes

Carbon Footprint
Often used to show CO2 production a
person is responsible for over one year

May be direct or indirect

Combustion – car use, gas furnace,...

Reduced vegetation (deforestation)

Carbon needed for activities or goods
–Cement, energy, food...
Carbon Footprint
.

Also used to show the carbon dioxide
formed for a specific activity or product:

e.g. air conditioner use, paper...
Models can also be used to predict future global
temperatures.
Black line = data for the 20th century
Other lines = projected 21st century temperatures based on different socioeconomic
assumptions
3.9

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
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Some results of 1°C Global Warming
Change in weather patterns

Some small areas could see cooling

But average temperatures increase
Sea ice disappears
Sea level rise – due to water expanding as
it warms up
More extreme weather
Loss of plant and animal species
Lose some fresh water sources
Loss of Polar Ice Cap
1979
2003
NASA Study: The Arctic warming
study, appearing in the November 1,
2003, issue of the American
Meteorological Society's Journal of
Climate, showed that compared to the
1980s, most of the Arctic warmed
significantly over the last decade, with
the biggest temperature increases
occurring over North America.
Perennial, or yearround, sea ice in the
Arctic is declining at a
rate of nine percent per
decade.
3.10
Some ways to reduce anthropogenic GG



Reduce energy use

All energy production has a carbon footprint

More efficient cars (higher mpg)

Coal power plants – largest footprint
Limit fertilizers

Production and use creates GG
Reduce food waste

Food production produces GG

Organic decomposition produces GG

Cap and Trade

Government limits GG emissions

Each company has a maximum amount
of allowed emissions.

If a company produces less than the
maximum, it can trade or sell this
unused allowance to less efficient
companies

This gives a financial incentive to
companies to invest in and develop
new technologies
A Cap-and-Trade System can be used to limit CO2
emissions.
3.11

Capture and sequestration

Proposed method to reduce carbon
footprint for coal power plants

Capture CO2 from exhaust and bury to
take this GG out of the environment

Not simple to isolate the CO2

Underground storage may eventually
leak

Prototypes for this process are being
investigated
One potential method for mitigation is CO2 sequestration.
3.11
Climate Adaptation



How well/quickly can the environment
adjust to compensate for the enhanced
greenhouse effect?
Warmer climates may increase plant growth
(land and aquatic), which would result in
increased CO2 absorption
The environment has adapted in the past to
extremely large changes in GG levels, but
this has also resulted in large scale
extinctions of many plants and animals
Amplification of Greenhouse Effect:
Global Warming
What we know:
1. CO2 contributes to an elevated global temperature.
2. The concentration of CO2 in the atmosphere has
been increasing over the past century.
3. The increase of atmospheric CO2 is a
consequence of human activity.
4. Average global temperature has increased
over the past century.
3.2
What might be
true:
1. CO2 and other gases generated by human activity are
responsible for the temperature increase.
2. The average global temperature will
continue to rise as emissions of anthropogenic
greenhouse gases increase.
3.9
Radiative Forcings are factors that affect the balance of
Earth’s incoming and outgoing radiation.
3.9
Intergovernmental Panel on Climate Change (IPCC)
Recognizing the problem of potential global climate change,
the World Meteorological Organization (WMO) and the
United Nations Environment Programme (UNEP)
established the Intergovernmental Panel on Climate Change
(IPCC) in 1988. It is open to all members of the UN and
WMO.
In 2007, the IPCC stated in a report that scientific evidence for
global warming was unequivocal and that human activity is the
main cause.
3.10
Conclusions from the 2007 IPCC Report
3.10
Kyoto Protocol – 1997 Conference
• Intergovernmental Panel on Climate Change
(IPCC) certified the scientific basis of the
greenhouse effect.
• Kyoto Protocol established goals to stabilize and
reduce atmospheric greenhouse gases.
• Emission targets set to reduce emissions of six
greenhouse gases from 1990 levels.
(CO2, CH4, NO, HFCs, PFCs, and SF6)
• Trading of emission credits allowed.
3.11