ATM S 111, Global Warming:
Understanding the Forecast
DARGAN M. W. FRIERSON
DEPARTMENT OF ATMOSPHERIC SCIENCES
DAY 2: 04/01/2010
A Confession…
 It’s all made up
 We did it for the
grant money
My Recent Grant Applications
 Hot in Herre: On Earth and in the Club
 TiK ToK on the Clock: Neither the Party Nor the
Carbon Dioxide Emissions are Going to $top
 The Hydrologic Cycle and Makin’ it Rain
How Grants Actually Work
 I currently have 3 grants:
 Two from the National Science Foundation (NSF), one from
National Oceanic and Atmospheric Administration (NOAA)
NSF #1: Tropical atmospheric circulation and global warming
 NSF #2: Processes that determine the midlatitude atmospheric
vertical structure
 NOAA: Natural climate variability of the tropics (the MaddenJulian Oscillation)



There are plenty of important natural weather/climate
phenomena to worry about…
Further, they’re reviewed by other scientists, so exaggerating
impacts doesn’t get you far
What Do Grants Pay For?
 My grants pay almost exclusively for graduate
students


Tuition & salary for them
Also undergrad research assistants
 I get up to 3 months (summer) salary from grants,
but having grants doesn’t increase my income

Grants also pay for visits to conferences, publication fees,
research equipment, etc.
 Grants are a significant source of income for the
university as well

UW took in over $1 billion in grant funds last year (we’re #1 in
the nation in federal grants)
Talk Tonight
 Plastic Solar Cells? Challenges and Opportunities
for Photovoltaics



David Ginger (UW Chemistry Department)
Kane 130, 6:30 PM
Reserve a seat at
http://courses.washington.edu/efuture/
Reading Assignments
 From last time:
 Make sure you’ve read Rough Guide p. 3-19 “Climate Change:
A Primer”
The Big Picture
 The Outlook
 What Can We Do About It

 Next reading assignment:
 Rough Guide p. 20-31 “The Greenhouse Effect”
 If it’s about hotels in Melbourne you might have bought the
wrong Rough Guide
Outline of This Lecture
 Review of: How exactly the Sun heats the Earth
 How strong?
 Important concept of “albedo”: reflectivity
 How the greenhouse effect works
 How the Earth cools
 And how greenhouse gases lead to less cooling
 What are the main greenhouse gases?
 And which are changed by human activity?
How Does Energy Arrive From the Sun?
 Energy from the Sun is called “shortwave
radiation” or solar radiation
 Radiation with shorter wavelengths is more
energetic
 This has long wavelength and low energy
 This has short wavelength and high energy
Average Solar Radiation
 Solar radiation at top of atmosphere is 1366 W/m2
 Average solar radiation on Earth is 342 W/m2
Reason for seasons:
Winter hemisphere is
tilted away from the
Sun, and gets less
direct sunlight
Solar Radiation on Earth
 30% is reflected back out to space
 Mostly by clouds, also some by the surface or by the
atmosphere
 20% is absorbed in the atmosphere
 50% is absorbed at the surface
 Next: how does the Earth lose energy?
“Longwave Radiation”
 The Sun is the energy input to the climate system
 How does the Earth lose energy?
 Turns out it’s also by radiation!
 But it’s not visible light like
from the Sun, it’s infrared
radiation AKA “longwave
radiation”
Infrared satellite image 
“Longwave Radiation”
 Everything actually emits radiation
 Depends partly on the substance but mostly on temperature
Neck = hotter
Hair = colder
Infrared thermometer
Longwave Radiation
 Higher temperature means more radiation
Eyes and inner ears are warmest: they
radiate the most
Nose is the coldest: it radiates less
Thermal night vision technology detects longwave radiation
Temperature & Radiation
 Higher temperature = more radiation and more
energetic radiation (shorter wavelengths)
 Explains the Sun’s radiation too

Sun is really hot 
It emits much more radiation
 It emits shortwave radiation instead of longwave radiation like
the Earth

Energy Into and Out of the Earth
 Heating/cooling of Earth
 The Earth is heated by the Sun (shortwave radiation)
 The Earth loses energy by longwave radiation (out to space)
“Energy Balance”
 If the energy into a system is greater than the
energy out, the temperature will increase

A temperature increase then results in an increase of energy out


Hotter things radiate more
This will happen until:
Energy in
Energy out
 When energy in equals energy out, we call this “energy
balance”
Energy Balance on Earth
 If the solar radiation into Earth is greater than the
outgoing longwave radiation, the temperature will
increase


A temperature increase then results in an increase of the
longwave radiation out (hotter things radiate more)
This will happen until:
Shortwave in
Longwave out
 Global warming upsets the energy balance of the planet
Energy Balance with No Atmosphere
 If there was no atmosphere, for energy balance
to occur, the mean temperature of Earth would be 0o
F (-18o C)
-18o C (0o F)
 Missing piece: the greenhouse effect
 All longwave radiation doesn’t escape directly to space
The Greenhouse Effect
 Greenhouse gases block longwave radiation from
escaping directly to space


These gases re-radiate both upward and downward
The extra radiation causes additional warming of the surface
Extra downward
radiation due to
greenhouse gases
15o C (59o F)
The Greenhouse Effect
 Greenhouse gases cause the outgoing radiation to
happen at higher levels (no longer from the surface)


Air gets much colder as you go upward
So the radiation to space is much less (colder  less emission)
15o C (59o F)
The Greenhouse Effect
 Greenhouse effect is intuitive if you pay attention to
the weather!
Cloudy nights
cool less quickly


In the desert, temperatures plunge at night!

No clouds & little water vapor in the desert: little greenhouse effect
What are the Major Greenhouse Gases?
 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 though

Just like the atmosphere is almost transparent to solar
radiation, the primary gases in our atmosphere are transparent
to longwave radiation
If our atmosphere was only nitrogen, oxygen,
and argon, this picture with no greenhouse
effect would be accurate!
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
suspended in air
 The number one greenhouse gas!
 Powerful because there’s a lot of it
 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

63% of the anthropogenic greenhouse effect so far
 Increases primarily due to
fossil fuel burning (80%)
and biomass burning (e.g.,
forest fires; 20%)


Preindustrial value: 280 ppm
Current value: 386 ppm
Carbon Dioxide
 CO2 will also be the main problem in the future
 It’s extremely long-lived in the atmosphere
 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
 Increases anthropogenically due
to farm animals (cow burps),
landfills, natural 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 concentrations have
been leveling off in recent years,
possibly due to drought in wetlands
at high latitudes
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 (or 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 (25 times more powerful) even
though it doesn’t stay as long
Nitrous Oxide
 N 2O
 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
 Ozone or 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
 Remember ozone depletion is not global warming!


Near the surface where it is caused by air pollution: “bad ozone”
 Bad ozone is a greenhouse gas, and is more potent on a
per molecule basis than CO2

But very very short-lived

Fun fact: Global warming potential for ozone is not usually calculated
– rather it’s wrapped into the GWPs of the other gases that lead to its
chemical creation
CFCs
 CFCs or chlorofluorocarbons are the ozone
depleting chemicals

Have been almost entirely phased out
 CFCs are strong greenhouse gases
 Their reduction likely saved significant global warming in
addition to the ozone layer!
 Some replacements for CFCs (called HFCs) are
strong greenhouse gases though
 Global warming
potentials of up to
11,000!
The Natural Greenhouse Effect
 Contributions to the natural greenhouse effect:
 H2O (water vapor): 60%
 CO2 (carbon dioxide): 26%
 All others: 14%
 These numbers are computed with a very accurate
radiation model

First running with all substances, then removing each
individual gas
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 same picture
from before, but more.
More radiation is trapped
before it gets out to space.
Longwave radiation is
emitted from a higher
(and colder) level on
average.
The Unnatural Greenhouse Effect
 Contributors to the “anthropogenic” greenhouse
effect

Numbers for the whole world up to this point:
Carbon dioxide: 63%
 Methane: 18%
 CFCs, HFCs: 12%
 Nitrous oxide: 6%

The Anthropogenic Greenhouse Effect
 Contributors to the “anthropogenic” greenhouse
effect

Numbers for the US
based on current (2008)
emissions
CO2 is the big problem in the US
currently.
Note how much lower the HFCs are
than on the previous slide. This is
b/c we basically don’t emit CFCs any
more.
From US EPA 2010 report (draft)
Summary
 The Earth is heated by the Sun
 This is shortwave radiation
 Albedo: key factor that determines how much radiation is
absorbed vs reflected
 Earth loses energy due to longwave radiation
 The greenhouse effect causes less efficient heat loss to space by
longwave radiation
 Greenhouse gases:
 Number one is water vapor
 Number two is CO2
 Global warming potential: total warming caused over a fixed
time period
Extra Credit Questions
 Climate change vs global warming?
 And ATM S 211 “Climate Change” vs ATM S 111 “Global
Warming”?
 Painting buildings white to increase albedo & cool
cities?
 Why does the Earth continue to warm even if CO2
remains fixed?