1. Systems
•• Open System:Open System: Energy and Matter can be exchanged
between systems
•• Closed System:Closed System: Exchange of Matter greatly
restricted, but may allow exchange of energy
•• Isolated System:Isolated System: No Energy or Matter can be
transferred in or out of the systemtransferred in or out of the system
•• Stable System:Stable System: resists change and reverts back to
this state when disturbed
•• Unstable System:Unstable System: Once disturbed the system
cannot return to the original state
•• MetastableMetastable System:System: Can have several stable states.
2. Feedback
• Processes in one system influences processes in
another interconnected system by exchange of
matter and energy. The exchange is called feedback.
•• Positive Feedback:Positive Feedback: Change in one system causes
similar change in the other system. Can cause
runaway instabilityrunaway instability
•• Negative FeedbackNegative Feedback means a positive change in one
system causes a negative change in the other
Changing CO2 induces positive water vapor feedback
Changing CO2 induces positive albedo feedback
3. Low frequency climate variability:
sub-seasonal variation, seasonal variation,
annual variation, and interannual variation.
4. Walker circulation
The Walker Circulation refers to an east-west circulation of the atmosphere above
the tropical ocean in the zonal and vertical directions, with air rising above
warmer ocean regions (normally in the west), and descending over the cooler
ocean areas (normally in the east). Its strength fluctuates with the change in sea
surface temperature.
5. El Niño and La Niña
El Niño is characterized by
unusually warm ocean
temperatures in the
Equatorial Pacific, as
opposed to La Niña, which
characterized by unusually
cold ocean temperatures in
the Equatorial Pacific. El
La Niña condition
the Equatorial Pacific. El
Niño is an oscillation of the
ocean-atmosphere system in
the tropical Pacific that is
closely related to the change
in the Walker circulation and
has important consequences
for weather and climate
around the globe.
El Niño condition
TahitiDarwin
6. Southern Oscillation
1958-1998
The Southern Oscillation is the atmospheric
component of El Niño/ La Nina. This component is an
oscillation in surface air pressure between the tropical
eastern Pacific and the western Pacific Ocean waters.
El Niño/La Niña-Southern Oscillation (ENSO)
Teleconnections via atmospheric Rossby waves
7. Impact of ENSO on Global Climate
8. ENSO and hurricane
• Less hurricane days during El nino years
mainly due to stronger vertical wind shear
• More hurricane days during La nina years
mainly due to weaker vertical wind shear.
9. Pacific Decadal Oscillation (PDO)
PDO is a long-lived ENSO-like pattern of Pacific climate variability
usually persisting for a long time period about 20-to-30 years.
ENSO and PDO are not the independent anomalies
but are somehow linked phenomena.
10. Some extreme climate anomalies
(a) A decade of western North American drought
could be related to both human activities and natural
climate anomalies, such as ENSO.
(b) A possible cause for the 2003 European heat wave is
the polarwaord migration of polar jets in a warm climate.
(c) The vanishing snow of Kilimanjaro may be due to the (c) The vanishing snow of Kilimanjaro may be due to the
fact that the maximum warming occurs in the mid
troposphere over the Equator.
11. Challenges of numerical simulation of climate
� Insufficient observations – leading to
inaccurate initial conditions;
� Chaotic nature of the atmospheric and
oceanic system;
� Inherent deficiency of numerical models
with limited resolution that fails to resolve with limited resolution that fails to resolve
sub-grid physical processes.
�Data assimilation;
�Ensemble forecast;
�Parameterization.
Our answers to face the challenges:
12. Cloud radiative effect
Cooling effect: reflecting solar radiation
Warming effect: absorbing and emitting longwave radiation
Shortwave cloud forcing:
-50 W/m2 (cooling)
Longwave cloud forcing:
30 W/m2 (warming)
Net cloud forcing ∆CRF: -20 W/m2 (cooling)
Current climate:
13. Cloud-climate feedback
feedback cloud negative 0 CRF
feedback cloud zero 0 CRF
feedback cloud positive 0 CRF
→<∆
→=∆
→>∆
The impact of clouds on global warming depends on how
the net cloud forcing changes as climate changes.
14. Cloud radiative effects depend on height.
gT
cT
cg TT ≈
cT aT
ac TT <<
Low cloud High cloud
SW cloud forcing dominates,
cooling effect
LW cloud forcing dominates,
warming effect
15. In general circulation models (GCMs), clouds
are the sub-grid scale processes and are not
resolved. They are represented parametrically in
models. The cloud-climate feedback is one of the
largest uncertainties in climate simulations.
16. Cloud formation
Two processes, acting together or individually, can lead to
air becoming saturated: cooling the air or adding water
vapor to the air. But without cloud nuclei, clouds would not
form.
17. Precipitation
Cloud droplets need to grow up to a certain size in order to
fall to the surface due to gravity
18. Aerosol feedback
Direct aerosol effect: scattering, reflecting, and absorbing
solar radiation by particles.
Primary indirect aerosol effect (Primary Twomey effect):
cloud reflectivity is enhanced due to the increased
concentrations of cloud droplets caused by anthropogenic
cloud condensation nuclei (CNN).
Secondary indirect aerosol effect (Second Twomey effect):Secondary indirect aerosol effect (Second Twomey effect):
1. Greater concentrations of smaller droplets in polluted
clouds reduce cloud precipitation efficiency by restricting
coalescence and result in increased cloud cover,
thicknesses, and lifetime.
2. Changed precipitation pattern could further
affect CCN distribution and the coupling between
diabatic processes and cloud dynamics.
19. Climate Scenarios and Emissions Scenarios
What is a scenario?
• Image of future
• Neither forecast nor prediction
• Each scenario is one possible future
• Useful tool for not fully understood complex systems, whose
prediction is impossible
• Emission scenario ≠ climate scenario• Emission scenario ≠ climate scenario
1. Population prospects
2. Economic development
3. Energy intensities and demand, structure of its use
4. Resource availability
5. Technological change
6. Prospects for future energy systems
7. Land-use changes
Main driving forces of future emissions:
20. Storylines of scenarios
A1: • Rapid economic growth.
• Peak population mid-21st century, then, declining.
• Rapid introduction of new and more efficient technologies.
• Substantial reduction of regional difference in per-capita income.
A2: • Regional solutions to environmental and social equity issues.
• Continuously rising world population.
A1FI: Fossil fuel intensiveA1B: Balanced emphasis on all energy sourcesA1T: Non-fossil fuel intensive
• Continuously rising world population.
• Slow per-capita income growth technological development
B1: • Rapid changes in economic structures.
• Peak population mid-21st century, then, declining, as in A1.
• Reduction in intensity of demand for materials.
• Introduction of clean and resource efficient technologies.
• Global solutions to environmental and social equity issues.
B2: • Intermediate economic development.
• Moderate population growth.
• Less rapid and more diverse technological change than in the B1 and A1.
• Regional solutions to environmental and social equity issues.
21. Uncertainties associated with Scenario Analysis and
climate change projection
Three types of uncertainties:
• data uncertainties,
• modeling uncertainties,
• completeness uncertainties.
22. Carbon-cycle feedbacks22. Carbon-cycle feedbacks
a. Warmer land b. Warmer ocean
c. Ocean acidification d. Pump problems
e. A sluggish ocean f. Rock weathering
The above processes can induce either positive
or negative carbon-cycle feedbacks. But overall,
positive feedbacks prevail!
23. Stabilizing atmospheric CO2 level
a. The lower the stabilization target,
the sooner peak emission of CO2
must occur, or we must cut back on
fossil-fuel use, e.g., to stabilize
CO2 level at 450 ppm, we would
reach peak usage before 2020.
b. Lower stabilization levels can be b. Lower stabilization levels can be
achieved only with lower peak
emission.
c. All stabilization targets require
sharp reductions in CO2 emission
after the peak. Low stabilization
targets require that the emission
rates fall below the current rates
within a few decades.
24. Changes in the Oceans due to global warming
Melting glaciers
Changes in deep-ocean circulation (slowing down)
Warmer surface waters
25. Polar Ice Melting25. Polar Ice Melting
Loss of ice = enhanced warming due to lower albedo
Arctic ice melting affects polar bear survival.
Food sources are dwindling for Arctic dwellers.
Sea level rise
26. Ocean acidity increaseSome atmospheric carbon dioxide dissolves in ocean
water. ----- Acidifies ocean
CoccolithophoresForaminifersSea urchinsCorals
Organisms threatened by Increased Marine Acidity
Corals
27. Rising Sea Level – already occurring
Main contributors:– Melting of Antarctic and Greenland ice sheets (most
important)
– Thermal expansion of ocean surface waters
– Melting of land glaciers and ice caps
– Thermal expansion of deep-ocean waters