ATM S 111, Global Warming:
Understanding the Forecast
DARGAN M. W. FRIERSON
DEPARTMENT OF ATMOSPHERIC SCIENCES
DAY 2: OCTOBER 6, 2015
In the News…
 India submits climate action plan
 Will have 40% renewable energy by 2030
 Cut “emissions intensity” of its economy by 35% by 2030
 Now all major emitters have pledged
 Draft of UN agreement released
 For the Paris meeting in Dec
 Extreme weather
 Hurricane Joaquin in SC, Bahamas
 French Riviera flooding
News
 UW Student Chapter of the American Meteorological
Society has its first meeting today

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ATG 610, 5-7 PM
Come by if you’re interested in weather, climate, and air
quality
 Extra credit assignment (very quick turnaround!):
 Send me your comments on this article by Thursday 4 PM
“South Carolina flooding is the type of event climate scientists have
warned about for years” by Andrew Freedman
http://mashable.com/2015/10/05/south-carolina-floods-globalwarming/
Last time…
 Shortwave radiation (AKA solar radiation)
 Radiation from the Sun
 Mostly visible light
 Mostly gets absorbed at the surface or reflected back to space
 Longwave radiation
 Radiation emitted by the Earth
 Infrared (invisible) radiation
 Greenhouse effect makes it harder for longwave radiation to
escape to space
The Greenhouse Effect
 Greenhouse effect is intuitive if you pay attention to
the weather!
Cloudy nights
cool less quickly


Old mariner saying:
“Stars bright, cold night”
Energy Balance
 Energy balance occurs when heating equals cooling
 When shortwave radiation in equals longwave radiation out
 If the Earth is out of energy balance, temperatures
must change
Outline
 What are the main greenhouse gases?
 And which are changed by human activity?
 Global warming potential: a way to compare how bad
different gases are for the climate
 How a tiny fraction of the atmosphere controls its
temperature
 Connections to the ozone depletion problem

Ozone itself and the chemicals that caused it
Atmospheric composition
 Our atmosphere is mostly
nitrogen (N2, 78%),
oxygen (O2, 21%),
and argon (Ar, 0.9%)

But these are not greenhouse gases
 Molecules with 1 atom or 2 of
the same atoms aren’t greenhouse gases

The primary gases in our atmosphere are thus transparent to
longwave radiation
Greenhouse Gases
 Polyatomic molecules are greenhouse gases
 Water vapor (H2O)
 Carbon dioxide (CO2)
 Methane (CH4)
 Nitrous oxide (N2O)
 Ozone (O3)
 Chlorofluorocarbons (the
ozone depleting chemicals which
have been banned)
The fact that they can rotate and vibrate means
they can absorb the right frequencies of longwave
Greenhouse Gases
 All greenhouse gases are a rather small fraction of
the atmosphere!



Water vapor has the highest concentration: 0.4%
CO2: 0.04%
Methane: 0.0002%
 “Trace gases” have a remarkable effect on the
atmosphere

E.g., ozone is less than 0.00001% of the atmosphere, but
absorbs essentially all harmful UV-B and UV-C radiation
 Let’s discuss each gas separately
Water Vapor
 Gas form of water
 AKA humidity
 Not the same as clouds – clouds are tiny droplets of water or
ice crystals suspended in air
 The number one greenhouse gas!
 Not controlled by humans!
 It’s a feedback not a forcing (topic of the next lecture)
 Observed to be increasing with global warming
Carbon Dioxide
 CO2
 It’s what we breathe out, what plants breathe in
 The primary contributor to the anthropogenic
(human-caused) greenhouse effect

Over 55% of the anthropogenic greenhouse effect so far
 Increases primarily due to
fossil fuel burning (90%)
and deforestation (10%)


Preindustrial value: 280 ppm
Current value: 400 ppm
Carbon Dioxide
 CO2 will also be the main problem in the future
 It’s extremely long-lived in the atmosphere
 Around 50% of what we emit quickly gets taken up by the
ocean or land



We’ll discuss this more later
Most of the rest sticks around for over 100 years
Some of what we emit will still be in the atmosphere over
1000 years from now!
Methane
 CH4

Natural gas like in stoves/heating systems
 Much more potent on a per molecule basis than CO2

Only 1.7 ppm though – much smaller concentration than CO2
 Natural sources from marshes (swamp gas) and other
wetlands

Video of methane release from tundra
lakes in Alaska & Siberia
 Increases anthropogenically due
to farm animals (cow burps),
landfills, coal mining, gas leakage,
rice farming
Methane
 The lifetime of CH4 is significantly shorter than
carbon dioxide


Breaks down in the atmosphere in chemical reactions
Lifetime of methane is only 8 years
Methane leveled off for a few years
(droughts in high latitude wetlands?)
Starting to rise again though
Global Warming Potential
 CO2 lifetime > 100 years
 Methane lifetime = 8 years
 But methane is a much stronger greenhouse gas
 How to put these on similar terms? Global
warming potential (GWP)

Global warming potential is how much greenhouse effect
emissions of a given gas causes over a fixed amount of time
(usually 100 years)


Measured relative to CO2 (so CO2 = 1)
Methane’s global warming potential is 25

Much more potent than CO2 even though it doesn’t stay as long
Nitrous Oxide
 N2O
 Laughing gas
 Also more potent on a per molecule basis than CO2
 Global warming potential: 310
 Comes from agriculture, chemical industry,
deforestation
 Small concentrations of
only 0.3 ppm
Ozone (O3)
 Don’t confuse ozone with global warming!
 The ozone depletion problem is essentially solved

And the ozone layer will be fully recovered in 50 years or so
Ozone (O3)
 Don’t confuse ozone with O-Zone
 Ozone: O3, gas in the atmosphere
 O-Zone: Moldovan pop band
Ozone
 Ozone (O3) occurs in two places in the atmosphere
 In the ozone layer very high up


This is “good ozone” which protects us from ultraviolet radiation &
skin cancer
Near the Earth’s surface

“Bad ozone”: caused by air pollution
 Bad ozone is a greenhouse gas, and is more potent on a
per molecule basis than CO2

But it’s very very short-lived

Global warming potential for bad ozone is wrapped into the other
gases which lead to its chemical creation
 Chlorofluorocarbons: what caused ozone depletion
CFCs & Thomas Midgley
 Thomas Midgley popularized chlorofluorocarbons
(CFCs) in the 1920s



Worked for General Motors (owned Frigidaire)
CFCs first used as a coolant in refrigerators
Also used in air conditioners, propellant sprays, foams
 Midgley was also the inventor of leaded
gasoline


Tetraethyl lead was used as a fuel additive, only
recently banned worldwide
One of the most harmful pollutants of the 20th
century
CFCs and the Ozone Hole
 Late 1960s: James Lovelock detected CFCs all over
the planet

Essentially all CFCs ever emitted were still in the atmosphere!
 1974: Molina and Rowland postulated that CFCs
could destroy the ozone layer
 1984: Ozone hole discovered over
Antarctica!


Worldwide ban came soon after
We now have completely phased out CFCs
Mario Molina
CFCs
 CFCs are strong greenhouse gases
 Global warming potentials of 5000 to 15000!
 Their phase-out saved significant global warming in addition
to the ozone layer
 Slowly declining but will persist for many decades
 Some replacements for CFCs (called HFCs) are
strong greenhouse gases too

Global warming potentials of up
to 15,000!
The Natural Greenhouse Effect
 Contributions to the natural greenhouse effect:
 H2O (water vapor): 60%
 CO2 (carbon dioxide): 26%
 All others: 14%
The Unnatural Greenhouse Effect
 Increasing levels of CO2 and other greenhouse gases
leads to a stronger greenhouse effect

With more greenhouse gases, it becomes harder for outgoing
radiation to escape to space
It’s like this picture from
before, but more…
The Unnatural Greenhouse Effect
 Contributors to the “anthropogenic” greenhouse
effect

Numbers for the whole world up to this point:
Carbon dioxide: 56%
 Methane: 32%
 CFCs, HFCs: 6%
 Nitrous oxide: 6%

Current US Contributions
 Contributors to the “anthropogenic” greenhouse
effect for the United States (2013)


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CO2 = 82.5%
Methane = 9.5%
Nitrous oxide = 5.3%
HFCs & related
substances = 2.6%
Summary
 Greenhouse gases:
 Number one is water vapor
 Number two is CO2
 Also methane, nitrous oxide, CFCs
 Global warming potential: way to compare different
greenhouse gases to CO2

Many other GHGs are stronger per molecule, but CO2 remains
the biggest problem