Complication in Climate Change Systems Open System: Energy and Matter can be exchanged between systems Closed System: Exchange of Matter greatly restricted, but may allow exchange of energy Isolated System: No Energy or Matter can be transferred in or out of the system

Stable System: resists change and reverts back to this state when disturbed Unstable System: Once disturbed the system cannot return to the original state Metastable System: Can have several stable states.

Feedback Processes in one system influences processes in another interconnected system by exchange of matter and energy. The exchange is called feedback. Positive Feedback: Change in one system causes similar change in the other system. Can cause runaway instability Negative Feedback means positive change in one system causes negative change in the other

Changing CO2 induces water vapor feedback 2CO2 experiment Positive feedback Non-constant water vapor 2CO2 experiment Constant water vapor

Ice albedo feedback Can you give a negative feedback example based on your every day life? What feedback is associated with cloud cover?

Climate variability Low frequency climate variability: sub-seasonal variation, seasonal variation, annual variation, and interannual variation. Sub seasonal variability is normally caused by the Internal nonlinear dynamic process of atmosphere. Longer than seasonal time scale variability is mainly controlled by anomalies in SST and air-sea interaction.

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 Niño is an oscillation of the ocean-atmosphere system in the tropical Pacific having important consequences for weather and climate around the globe. 2011 El Niño

Walker circulation

Bjerknes’s (Nov. 2, 1897- Jul. 7, 1975, Norwegian- American meteorologist) air-sea interaction argument What causes the turnabout from warm phase to cold phase? Why do El Niños typically last only 12-18 months? Why do they usually shut down rapidly and switch from warm phase to cold phases or from cold phase to warm phase? Walker circulation Weakened Walker circulation

Equatorial wave theory --- a negative feedback process to shut down El Nino Rossby wave Rotation and Vorticity Relative vrticity Cyclone Anti-cyclone Absolute vorticity=Planetary vorticity + Relative vrticity

Absolute vorticity is not conserved is conserved Potential vorticity conservation:

Rossby Wave Westward propagation Cyclonic circulation P-1 H h P S (warm) N (cold) Anti-cyclonic circulation Rossby Wave Westward propagation

Jet stream

Kelvin wave a. Small scale Kelvin wave

b. Large-scale Kelvin wave In a rotating frame, large-scale kelvin wave must be: 1. a boundary wave. 2. propagating with the boundary on its right in the North. hemisphere. 3. a trapped wave decaying from the boundary. c. Equatorial Kelvin wave P C C P North South X X

Western Pacific Eastern Pacific warm cold El Niño year Thermocline Normal year Rossby wave upwelling upwelling downwelling Equator downwelling Kelvin wave Rossby wave upwelling upwelling thermocline

Vertical temperature anomalies along the equator during 1997-1998 El Niño event. February 1997 160W 80W January 1998

Southern Oscillation Sea level pressure anomaly at Tahiti and Darwin 1958-1998 Sea level pressure anomaly at Tahiti and Darwin

Southern Oscillation Index (SOI): defined as the pressure difference between Tahiti in the southeast Pacific and Darwin in the western Pacific. Negative SOI corresponds to El nino Positive SOI corresponds to La nina. (ENSO)

Impact of ENSO on Global Climate Rainfall anomaly during 1997-1998 El nino East Europe California East China Florida India Indonesia Amazon Southern Africa East Africa Northern Australia Uruguay Why an anomaly, such as ENSO in the equatorial region, can affect climate thousand miles away in mid and high latitude?

Teleconnections

ENSO and global warming: Is there a connection? Several arguments 1. In the last 20 years, there have been more El Niños then La Niñas, whereas historically the two have occurred in about equal numbers. 2. El Niño serves as a mechanism for tropics to get rid of heat. 2. ENSO changes global precipitation pattern and intensity

WMO organized an intercomparison study by comparing the simulated ENSO in the next century in response to global warming by many different global climate models at the atmospheric research centers all over the world. They have looked at (1) the mean state of ENSO and (2) variability of ENSO. Mean state of ENSO

Variability of ENSO The inter-model difference is about as large as the natural variability from the second half of the 19th century to the middle of the 20th century!