Dynamics of Climate Variability & Climate Change EESC W4400x Fall 2006

1. Dynamics of Climate Variability & Climate ChangeEESC W4400xFall 2006 Instructors: Lisa Goddard, Mark Cane Teaching Assistant: Philip Orton

2. Objectives: Knowledge Understand fundamental physical processes underlying climate variability and climate change Understand how models and predictions work Understand important influencing factors (in models & predictions) and important assumptions/uncertainties EESC W4400x

3. Objectives: Skills Climate science literacy: Read with understanding (i.e. be able to summarize and interpret) articles on the topics covered in this course in journals such as Science and Nature. Forecast interpretation: Identify influencing factors and uncertainties for climate predictions on time scales, from seasonal-to-interannual forecasts to climate change projections. EESC W4400x

4. OUTLINE • “Climate” • Models • Systems and Feedbacks EESC W4400x

5. Climate System EESC W4400x

6. What is Climate? • Climate is the mean stateof the environment, defined over a finite time interval, at a given location and time. - This state can be characterized by the mean values of a range of weather variables, such as wind, temperature, precipitation, humidity, cloudiness, pressure, visibility, and air quality. • The definition of climate also includes the typical range of variabilityin values of environmental variables (for example – the standard deviation of temperature). • A complete description of the climate system and the understanding of its characteristics and change require the study of the physical properties of the high atmosphere, deep ocean, and the land surface, and sometimes the measurement of their chemical properties. • The study of climate is a quantitative science, involving the understanding of the transfer of energy from the sun to the earth, from earth to space, and between atmosphere, ocean, and land, all under fundamental physical laws such as conservation of mass, heat, and momentum. EESC W4400x

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8. Mean Temperature Field EESC W4400x

9. Remove mean Regional Temperature Variability EESC W4400x

10. Example:Time Scales of Variability EESC W4400x

11. Modeling the Climate EESC W4400x

12. Models • Conceptual Illustrate principal relationships or balances • Empirical/statistical Describe relationship between observed parameters (e.g. sea surface temperature and rainfall) • Numerical/dynamical Based on set of mathematical equations describing physical processes, that allow the system to evolve in time EESC W4400x

13. How do we model climate?[physically] • Physical/dynamical equations - 3-D equations of motion (conservation of momentum) - Continuity equation (conservation of mass) - Thermodynamic equation (conservation of energy) - Equation of state for air - Balance equation for water vapor • Parameterizations Small-scale processes that are treated statistically and their effects related to average conditions over much longer periods of time and larger space scales e.g. clouds, radiative transfer, turbulence EESC W4400x

14. Hierarchy of Climate Models(Physically-based) • 3-D coupled ocean-atmosphere GCMs (CGCMs) • 3-D atmosphere-only GCMs (AGCMs) • 2-D(λ,φ) – “barotropic” or 2-D(φ,z) – “Energy Balance” models • 1-D(z) – “Radiative-Convective Models” (RCMs) or “Single Column Models” (SCMs) • 0-D – Global-Mean Energy Balance Models EESC W4400x

15. ClimateChange Decadal Initial & ProjectedAtmospheric Composition Weather & Climate Prediction Initial & ProjectedState of Ocean Initial & ProjectedState of Atmosphere CurrentObservedState Uncertainty EESC W4400x Time Scale, Spatial Scale

16. Systems & Feedbacks • Example 1: Albedo (daisies) & temperature  “Daisyworld” EESC W4400x

17. Example 1 (cont.) Temperature as Function of Daisy Coverage EESC W4400x

18. Example 1 (cont.) Daisy Coverage as Function of Temperature EESC W4400x

19. Example 1 (cont.) x x Equilibrium & Stability System of Equations: D = Dmax – (T-To)2 (1) T = Tmax – αD (2) (1) Dmax (2) To x Tmax EESC W4400x

20. Snow/Icecoverage Surfacetemperature Systems & Feedbacks • Example 2: Albedo (snow/ice) & temperature As temperature decreases, snow/ice coverage increases (less snow/ice melted, and more precipitation delivered in frozen form) As snow/ice cover increases, temperature decreases (albedo increases, so less solar energy is absorbed by surface)  Positive feedback (Snowball Earth, Chp. 12 – Kump et al.) Potential negative feedback: As temperature drops, atmosphere holds less H2O, and precipitation decreases. Also, ice may begin to sublimate. EESC W4400x