Global Warming Exam Review

1. Global WarmingExam Review GEO 307 Dr. Garver

2. Exam Material • Archer chapters 1 – 5 • Circulation ppt, Atm Structure ppt • Starred links & videos • Homeworks • Quizzes

3. Chapter 1: Humankind & Climate • Weather vs. Climate • General introduction to global warming • What it is • Evidence of • Forecasting Climate Change • Assessing the risk • Models • Size of T inc. • Human vs. natural variability

4. T of Earth = balance of energy in & energy out. • change T of Earth by changing incoming or outgoing energy. • gases in the atmosphere • gh effect • human activity

5. Chapter 2: Blackbody Radiation • Electromagnetic Radiation • Black Body • All objects that have a T greater than 0 deg K emit radiation • Stefan-Boltzman Law • Weins Law What are the similarities and differences between the Sun and Earth radiation curves?

6. Radiative Equilibrium • Energy gained through absorption of short wave radiation is equal to the emitted long wave radiation If the T of an object is constant with time, the object is in radiative equilibrium at Te Is the earth in radiative equilibrium?

8. Chapter 2 summary • EMR carries energy through space • If an object can absorb energy, it can also emit energy. • Objects emit at a rate equal to T4

9. Boundary to Space VIS IR Atmosphere Chapter 3: Layer Model • Go from Bare rock model vs. Layer model • Algebraic calculation of the effect of an IR absorber (a pane of glass) on the equil. T of the Earth. • Not accurate or detailed • Not used for global forecasts • Start with bare rock • Then add pane of glass

10. Simple model of Earth T • Layer model • Toy system to learn from • T of Earth is controlled by ways that energy comes from Sun and is re-radiated to space as IR. • Assumption: energy in = energy out

11. Solar Constant Day Night Incoming solar energy • Incoming sunlight = Iin = 1350 W/m2 • 1350 W/m2 (1 - ) = 1000 W/m2 • Want flux for the whole planet (no m2) • Fin(W) = Iin(W/m2) x Area(m2) Area (m2) = r2earth

12. Put them together, total incoming flux is: • Fin = r2earth(1 - ) Iin • Remember: Fin = Fout • Iin = 1350 W/m2 • Reduce by albedo to 1000 W/m2 • Multiply by area of circle to get Flux (W)

13. Rate at which Earth radiates energy is given by SB law: • Fout = Area x esT4earth • e = emissity, 0 to 1, unitless Total energy flux from Earth Fout= 4r2earthesT4earth Asphere = 4r2earth

14. Fin = Fout r2earth(1 - )Iin = 4r2earthesT4earth (1 - )Iin Flux out Flux in esT4earth

15. Tearth = 4 (1 - ) Iin 4es • Now we have a model that shows the relationship between 2 crucial climate quantities: • Solar intensity • Albedo • But, if we calculate Tearthwe get 255 K (-15˚C). • This is too cold, why?

16. Layer Model with GH Effect • Planet with pane of glass for atm. • Transparent to incoming VIS but blackbody to outgoing IR IR VIS IR IR

17. esT4ground Finally, a budget for the Earth overall: • Draw a boundary above the atm and figure that if energy gets across the line in, it’s flowing out at the same rate. • Iup,atm = Iin,solar • The intensities are comprised of individual fluxes from the Sun and the atm. esT4atm = (1-a)Isolar In = Out 4 2esT4atm

18. Skin T - Place in the Earth system where the T is most directly controlled by the rate of incoming solar energy is the T at the location that radiates to space (equal to Tatm) In = Out Skin T 2esT4atm esT4ground

19. Result is that the T of the ground must be warmer than the skin T by ~19%. 2esT4atm Warmer by about 19% esT4ground

20. Take Home Points • The outflow of IR energy from a planet must balance heating from the Sun. • The planet accomplishes this balance by adjusting its temperature. • Absorption of outgoing IR by the atmosphere warms the surface of the planet, as the planet strives to balance its energy budget

21. Chapter 4: Greenhouse Gases • Layer model assumes atm acts as a blackbody • In reality, gases absorb very selectively. • Some radiation bands are completely absorbed. • Others are ‘atmospheric windows’ • Difference has to do with the effect of molecular vibrations on the electromagnetic field.

22. Gases, vibration,light • Gases are the simplest types of molecules. • Vibrate only in a particular frequency • Vibrations of the major gases in the atm (O2, N2) are invisible to the electromagnetic field • Symmetrical molecules • only 2 atoms (that are the same) • Not IR active

23. Gases, vibration,light • Water – main absorber - 0 to 4% - ~70% • negative feedback effect • Water vapor spectroscopy very complex • vibrates in a number of ways • All interact with IR light • Gas molecules with more then 2 atoms have more than one chemical bond.

24. Most climatically important IR Active Gases, vibration,light • Straight line with C in the middle • symmetric state - both O molecules pull equally. • asymmetric state

25. 1. Nitrous Oxide (N2O) 2. Methane (CH4) 3. Ozone (O3) 4. Water Vapor (H2O) 5. Carbon Dioxide (CO2) Sun – Range of visible wavelengths Earth – Range of primary wavelengths being emitted.

26. How gh gases interact with IR • Gases are not good blackbodies! • choosy about frequency • blackbody spectra for Earth • ranges from hot summer day to cold upper atm (model generated data) Jagged curve – IR light measured by a spectrophotometer looking down CH4 – 1300 cycle/cm CO2 effects outgoing IR more because there’s more energy at 700 cycle/cm 50 mm 10 mm 7.0 mm

27. Atm w/no CO2 Atm w/10 ppm CO2 Atm w/100 ppm CO2 Atm w/1000 ppm CO2 Band Saturation

28. Methane & CO2 • A molecule of CH4 is 20x • More powerful than a molecule of CO2

29. CO2 - most prominent gh gas • Recycled through photosynthesis

30. Keeling Curve 400+ ppm

31. Keeling Curve • Previous 800,000 years, CO2 levels never exceeded 300 ppm • There is no known geologic period in which rates of increase have been so sharp. • Was about 280 ppm at the advent of Industrial Revolution • “I wish it weren't true, but it looks like the world is going to blow through the 400-ppm level without losing a beat," said Scripps geochemist Ralph Keeling, who has taken over the Keeling curve measurements from his late father. "At this pace we'll hit 450 ppm within a few decades."

32. The 3 most powerful greenhouse gases are; • Water vapor • Carbon dioxide • Methane • Misc trace gases: • Ozone, N20, CFCs (HFCs)

33. Take Home Points • Gases absorb/emit IR energy if they vibrate at the frequency of the IR energy, and if its vibration effects the electric field. • O2 and N2 are not gh gases • All molecules of 3 atoms or more are IR active. • A gh gas has a strongest impact on the radiative balance of Earth if it interacts with energy in the middle of the earth energy spectrum. • Band saturation: a gh gas at high concentrations will be less effective molecule by molecule than a dilute gas.

34. Chapter 5: Temperature Structure of the Atmosphere • T structure of atm is coupled to T of ground by convection. • Leads to dec. in T with inc. altitude. • If atm were incompressible, like water, there would be little change in T with altitude. • no gh effect because amount of outgoing IR would be the same whether it came from the ground or high in the atm.

35. Typical T and P of atm as a function of altitude

36. Adiabatic expansion • Lapse rate • Adiabatic • Dry vs. moist Water vapor • Latent heat • Condensation - LH SH

37. Convection in the layer model • Layer model from chapter 3 didn’t have convection. • T of each layer dec. with altitude • But, heat is only carried upward by radiation. • Need to add convection to the model.

38. Structure of Atmppt • Troposhpere • Stratosphere • Chemical composition • General concept of hadley cells/global cirulation

39. Take Home Points • P decreases with altitude • T decreases as a gas expands • LH is released as SH as water vapor condenses. • Lapse rate is controlled by the moist adiabatic. • Strength of gh effect depends on the lapse rate.

40. Circulation ppt • Review general circulation of atm as it relates to the class.