This Week: Future Climate
Future CO2 Forcing
Climate Sensitivity – Feedbacks
Natural Short and Long-term Forcings
Global Warming Impacts
Announcements
• See handout and website for details
regarding paper and poster content
• Poster Sessions: March 12 and 13 in
Mary Gates Commons 10:30 – 11:20
• Monday March 17 8:30 AM, Final
Exam, JHN 075 (here)
• Papers and descriptions of 3 other
posters due Wednesday March 19
Kaya Identity Model
kaya identity model
Future Atmospheric CO2
One emission scenario
Range of predictions suggest
double pre-industrial by midcentury
Figure 10.20
Stabilization Scenarios
What our emissions
can be for different
constant CO2 levels.
What do these tell
us about future
biosphere and ocean
sinks?
2000
2100
2200
2300
Committed to Warming: Time Response
Figure 10.4
A Long View of Fossil Fuel Perturbation
Figure 7.
Climate Sensitivity-All about Feedbacks
T = F
 is climate sensitivity parameter
 units: K “per” W/m2
  determined by feedbacks!
Estimates of Climate Sensitivity
T change for a 4
W/m2 forcing (i.e.
“double CO2”)
Most probable  ~
0.75 K/(W/m2)
Box 10.2, Figure 1
Announcements
• Get a handout on paper/poster
guidelines
• Brian’s office hours today canceled,
moved to Thursday 5-6pm
• My office hours are today, 3:30 –
4:30pm in 506 ATG
Feedbacks
+/+/Initial Forcing
State Variable
+ increases state variable
- decreases state variable
“feedback loop”
Process or
coupling
Ice-Albedo Feedback
Example of a positive feedback
+
+
Initial Forcing
(e.g. GHG)
More solar
radiation
absorbed
Temperature
Ice melts,
dark soils
exposed
Albedo
-
Water Vapor-Temperature Feedback
Increased
Greenhouse
effect
+
+
Initial Forcing
(e.g. GHG, solar
radiation)
Temperature
Water Vapor
+
More evaporation,
saturation vapor
pressure increase
Atmosphere—Protector of the Oceans?
water trap
If H2O reaches top of atmosphere
it is blown apart by UV radiation
H atoms escape to space, never to
return
Probable cause for no H2O on Venus
IR Flux-Temperature Feedback
Example of a negative feedback
+
Initial Forcing
(e.g. GHG)
Temperature
Outgoing IR
flux increases
+
Phytoplankton-DMS-Marine Cloud Feedback
Charlson, Lovelock, Andreae, Warren
“C.L.A.W.” Hypothesis
aerosols and
cloudiness
+
Initial Forcing
(decreased clouds)
+
-
Biogenic Sulfur
Emissions
Solar Radiation
(Temperature)
+
Photosynthesis
+
Cloud Forcings and Feedbacks
Low altitude thick clouds
 Stratus
High altitude thin ice clouds
 Cirrus
Aircraft emit particles (and particle
precursors) which can nucleat clouds. This
activity gives rise to a
57%
1. Positive radiative
forcing
2. Negative radiative
forcing
eg
N
Po
si
tiv
e
at
iv
e
ra
d
ra
ia
t
di
a
iv
e
tiv
e
fo
r ..
.
fo
...
43%
Aviation Contrails—Positive Forcing
October 2004
Clouds and Climate—a complex problem
Cirrus: Not so reflective, but
absorb and emit at cold T
Low Clouds: Absorb IR but emit
like warm surface. Reflective
Clouds and Cloud Feedbacks
Uncertain!
Albedo
+
+
Low Clouds
Temperature
+
Atmosphere holds
more water
Initial Forcing
(e.g. GHG, solar radiation)
+
Increased
greenhouse
effect
+
Temperature
Atmosphere holds
more water
High Clouds
+
Predicted Changes in Cloud Forcings
IPCC 2007
Sunspots – Cyclic Changes in Solar Output
~11 year Sunspot Cycle
Radiative Forcing by Solar Cycle
The solar cycle forcing has increased from -0.1 to
0.2 W/m2 since 1900. This forcing can explain
____ of 1oC increase in global Avg. T since 1900
1. 60 - 70%
2. 40 - 50%
3. 20 - 30%
75%
20%
0%
20
-3
0%
-5
40
60
-7
0%
5%
False Assertions: Sun – Global Warming
WRONG Solar Cycle
WRONG T record
Originally from WSJ Article written by two chemists named Robinson
False Assertions: Sun – Global Warming
Correct cycle
Laut 2003
T Response After Major Eruptions
Natural and Anthropogenic Forcings
Figure 6.13
El Nino Southern Oscillation-ENSO
Neutral Walker Circulation
Neutral
El Nino/La Nina State Flip-Flop
El Nino/La Nina Circulation Patterns
Strong La Nina
Very Strong El Nino
ENSO “Periodicity”
El Niño years
La Niña years
El Nino Global Impacts
El Nino Impact on Fish
Normal
El Nino
Climate History
18O
Ratios in Sediment and Ice Core
Pleistocene Glacial and Interglacials
February
Reconstruction of land and
sea ice 21,000 years ago
(last glacial maximum)
July
Records of NH Glaciations
Geological Records: glacial deposits, scarring, larger scale
Cordilleran Ice Sheet
Lake Missoula
Spokane Floods (from Lake Missoula)
Milankovitch—Before sediment cores
Predicts glacial and interglacial transitions
based on variations in Earth’s orbit
His results suggested many such transitions
in ~ 1 million yrs (he was right)
—at the time, no observable records show
that many, so his work widely criticized
Milutin Milankovitch
Milankovitch Continued
While lacking patience for critics,
he did not lack confidence
Milutin Milankovitch
“I do not consider it my duty to give an
elementary education to the ignorant, and I
have also never tried to force others to use
my theory, with which no one could find fault.”
Orbital Forcing Summary
Precession
Tilt
Eccentricity
IPCC 2007
Orbital Forcing Summary Cartoon
• orbital forcings
Currently NH summer takes place at aphelion, in
about 12,000 years, NH summer will occur at
perihelion. At this time, SH seasonality will be
1. stronger
2. weaker
54%
ke
r
ea
w
st
ro
ng
e
r
46%
Solar Insolation at 65N and Glaciation
Recent UW Research
Time rate of change of ice volume and solar insolation
The Key For Glaciation
Solar insolation in NH summer appears to be key
maintaining glaciation. Ice sensitive to melting!
Positive Feedback—
Destabilizing Climate
Initial Forcing
Weaker NH
summer insolation
Albedo
T
+
+
Ice Coverage
Same old ice-albedo feedback, just different initial forcing
Questions—In Class Activity
1.
Given the behavior of CO2 and CH4
is there a positive or negative
feedback with T?
2. Provide a feedback involving marine
biota which might explain CO2’s
behavior.
3. Suppose marine biota are the cause
of CO2’s behavior, is this support
for or against Gaia theory?
4. When’s the next glacial maximum?
Do you think we’ll get there?
Eccentricity: More to Less Circular
Obliquity: More or Less Seasonality
Precessional Cycle: Tilt and Eccentricity
Current situation