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