This Week: Anthropogenic
Climate Forcings (global warming)
Stratospheric Ozone Depletion
Greenhouse Gas Concentrations
Albedo
Part 1—Ozone
Reading: Chapter 17 of your text and WMO
Assessment (twenty questions): linked to course
web page.
•Ozone’s Role in Climate—Good and Bad Ozone
•Stratospheric Ozone’s Natural Sources and Sinks
•Stratospheric Ozone Depletion
• the “Ozone Hole”
Announcements
•Problem Set due tomorrow (Tues) in lecture
•Midterm exam Friday in discussion section
•My Office Hours: Today 5 – 6 pm and
Thursday 3:30 – 4:30 both in 506 ATG
•Midterm Review Session: Thursday 5pm-6pm
310c ATG
Atmospheric Ozone
Ozone Watch Web Page
Human changes to ozone are NOT the
cause of increasing avg. T
Human changes to ozone are example
of anthropogenic climate forcing
Ozone and Oxygen
Very Reactive
Very Un-reactive
Reactive
Vertical Distribution of O3
Effects of Human Activities
Increased surface and Upper Trop. O3
Decreased stratospheric O3
increased UV exposure (bad) increased health problems (bad)
increased greenhouse effect (bad)
Houston, Smarting Economically From
Smog, Searches for Remedies
By JIM YARDLEY
Published: September 24, 2000, NYT
''Smell that,'' went a popular local refrain during the 1960's.
''That's prosperity.''
But no one is bragging about the city's bad air anymore. This
year, Houston is narrowly leading Los Angeles for the unwanted
title of the nation's smog capital. It had 38 days in which smog
levels exceeded federal standards. The Environmental Protection
Agency is threatening sanctions if something is not done. On
Monday, readings of ozone, a primary ingredient in smog,
were so high that residents in some neighborhoods were
advised to stay indoors.
Ozone Damage
Needle damage (tip necrosis)
is a common sign of ozone
damage on pines.
Often observed in forests
downwind of major urban
areas—Sierra Nevada, New
England, Mexico City, etc.
Which is a better greenhouse gas: O3 in urban
smog or O3 in the upper troposphere – lower
stratosphere?
75%
1. Urban smog
2. Upper trop. –
lower strat.
U
pp
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tr
op
.
–
U
lo
rb
a
n
w
er
sm
og
st
ra
t.
25%
Explaining Stratospheric O3
1930 Sydney Chapman proposes first explanation
for O3 formation and loss in stratosphere:
(this part
was wrong)
O2
UV
Radiation
O
O3
Chapman Wasn’t Completely Right
Too much ozone predicted
Need a faster ozone removal
Stratospheric O3 Production: Chapman Right
Catalytic O3 Destruction: Chapman Missed
O3 is naturally destroyed by catalytic cycles involving
ultra trace nitrogen and hydrogen oxides
O2
X
O3
O
XO
O2
Catalytic “O3 Grinder”
“X” can be NO, OH, Cl,… at parts per trillion levels
Chlorofluorocarbons (CFCs)
Non-toxic, non-flammable,
easily compressible gases
Used as refrigerants and as
propellants in spray cans
Thought to be ideal…due to
safety and durability.
“Aerosol” Spray Cans: NOT SAME AS
ATMOSPHERIC AEROSOL PARTICLES
Early Warning Signs
Nature, June 28, 1974
Molina, Rowland, and Crutzen win Nobel Prize in 1994
CFC-11 Atmospheric Abundance
Mixing ratio
CFCs banned
Molina and Rowland
warning
Year
The Ozone Hole
Discovery of Antarctic Ozone Hole
1950
1970
1980
Vertical Structure of Antarctic Ozone Hole
Antarctic Ozone Hole Conundrum
• What is the cause?
• Why only in springtime between 15 – 25 km ?
• Why primarily in the Antarctic?
Antarctic Ozone Hole Theories
Also a scientific debate
chemistry versus meteorology
human versus natural
solar cycles
(ppb)
(ppt)
“Human Finger Prints”: Chlorine
ClO and O3
anticorrelated
Polar Stratospheric Clouds (PSC’s)
Chemistry on Polar Stratospheric Clouds
PSCs allow “inactive” chlorine to become “active”
sunlight
harmless chlorine
active chlorine
(destroys O3)
Turco, 1987
PSC Formation Requires Very Low T
Polar Vortex—
cuts off polar region
Seasonal Evolution of Ozone Hole
Polar Vortex
Ozone
Polar Stratospheric Clouds
Active Chlorine
Inactive Chlorine
May June
July
Aug.
Sept.
Oct.
Nov.
Dec. Jan
The lower stratosphere has been cooling
over the past decade+, by 1 – 3 K/decade.
This cooling should
1. Enhance polar
ozone depletion
2. Diminish polar
ozone depletion
85%
im
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h
po
po
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r
la
r
oz
oz
on
.
on
.
..
..
15%
In terms of global ozone, stratospheric
cooling should
68%
1. Enhance
destruction rates
2. Diminish
destruction rates
im
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io
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..
n.
..
32%
Ozone Watch Web Page
Total Ozone Changes Since 1980
Montreal Protocol
Montreal, 1987: First legally binding
international agreement
By 1992: a near complete ban on
production and use of CFCs.
Replacements for CFCs, known as
HCFCs fairly easily implemented
Ozone Recovery Predictions
Stratospheric Ozone Depletion--Summary
• Human emissions of CFCs are the largest
source of stratospheric chlorine
• Chlorine is a catalyst for ozone destruction
• Total ozone has decreased by 4 – 6%, globally
averaged. Bigger changes at higher latitudes
• Each Antarctic spring, ~ 60 – 70% of ozone
over that region is destroyedozone hole
Announcements
• Exam Friday in Discussion
• Review Session Thursday 5 – 6:30pm
TBD (either 310 ATG or JHN 075)
• Interesting Seminar today at 12:30 in
JHN 011—Early Mars and Early Earth
Quantifying Perturbations to Climate
• Forcings: long-term perturbation
• Human Forcings on Climate
– Ozone, LLGHG, Aerosols, Land Use
– CO2 Forcing in detail
• Natural Forcings and Climate Variability
Climate Forcings
a perturbation, directly or indirectly,
affecting Earth’s energy budget
FIN
FIN + F
Temperature
Temperature
FOUT
FOUT
Long-Lived GHG Concentrations
Carbon Dioxide: CO2
Fossil Fuel Burning
Methane: CH4
Agriculture and Gas Use
Nitrous Oxide: N2O
Agriculture
Figure SPM.1
Scattering of Radiation by Aerosol
Efficiency calculated assuming green light (0.5 m)
Typical U.S. Aerosol Size Distributions
Maxima are most common sizes
volume frequency
Fresh
urban
Aged
urban
rural
remote
Warneck [1999]
Visibility Reduction by Aerosol (Haze)
•
clean day
moderately polluted day
Acadia National Park (Northeastern Maine)
http://www.hazecam.net/
Aerosols Increase Earth’s Albedo
Aerosols scatter a fraction
of incoming solar radiation
back to space
This is known as the “direct
forcing” of aerosols.
Smoke particles from biomass
burning in Southeast Asia appear
as white haze
F ~ - 0.9
from
direct effect of aerosol
W/m2
modis.gsfc.nasa.gov
Ship Tracks and Contrails
Examples of Aerosol Indirect Effects on Clouds
“Sulfate Forcing” Mid 20th Century
Aerosol direct effect thought to explain
temporary hiatus in T increase
Cloud Albedo Effect: Radiative Forcing
• Aerosol - cloud
interactions: complex!
nonlinear, composition
and size dependent
• IPCC only estimates
aerosol effect on warm
(liq) clouds
• “cloud albedo effect” =
- 0.2 to -1.9 W/m2
Land Use Changes
IPCC 2007
Figure 2.15
Global Radiative Forcing of Climate
IPCC [2007]
FAQ 2.1, Figure 2
Atmospheric CO2 and Source Attribution
Fuel Combustion:
CH2O + O2  CO2 + H2O
If CO2 increase due to fuel
burning O2 should decrease
Figure 2.3
Human Perturbations to Carbon Cycle
Fossil Fuel Combustion ~ 6.5 GtC/yr currently
Deforestation ~ 1.7 GtC/yr currently (mostly in tropics)
Fossil Fuel Emissions and CO2 Growth Rate
If 100% of Human emissions
remained in atmosphere
Actual atmospheric increase
Fraction of emitted CO2
remaining in atmosphere
Present Day CO2 Sources and Sinks
8 Gt C/yr
Atmosphere
?
4 Gt C/yr ?
Total loss rate
Terrestrial
Biosphere
Ocean
Where is the 4 GtC going each year?
“Directly Measuring” Terrestrial Sink
Measure CO2 going into
forest.
Not easy to extrapolate,
but have a global network
Instead: quantify ocean
sink, and remainder must
be terrestrial biosphere
Determining Ocean Sink
Measure flux into and out of ocean, and
calculate expected amount of uptake based
on fairly well-known InorgC ocean chemistry
Trends in O2 Confirm CO2 Uptake
Present Day CO2 Sources and Sinks
8 Gt C/yr
Atmosphere
2 Gt C/yr
Terrestrial
Biosphere
2 Gt C/yr
Ocean
Will these sinks increase, decrease or stay the same?
Perturbed Carbon Cycle
~ 3000 – 5000 GtC are present as fossil fuels. If
we burn all available, can the terrestrial biosphere
remain an important sink?
61%
1. Yes, likely
2. No, unlikely
o,
N
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lik
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el
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39%
Suppose we wanted atmospheric CO2 to stop
increasing. By how much would we need to
cut emissions?
1. 20%
2. 35%
3. 50%
87%
%
50
%
7%
35
20
%
6%
The Kyoto Protocol aims for Carbon
emissions to be 6% lower than 1990 values
(~7GtC/yr). This level of reduction
56%
1. is too small to be
important
2. Can make a big
difference
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44%