1. Global Energy Balance Chautauqua UWA-6, Dr. E.J. Zita 9-11 July 2007 Fire, Air, and Water: Effects of the Sun, Atmosphere, and Oceans in Climate Change and Global Warming

2. Q: What sets Earth’s surface temperature?

3. Review: Temperature, heat, transport, …

4. Review: Convection and Radiation

5. Review: Blackbody radiators Intensity of radiation =  T 4

6. Review: Energy, power, and radiation Force = mass * acceleration [units: N = kg*m/s 2 ] Energy = work [units: Joules = N*m = kg*m 2 /s 2 ] Power = Energy / time = rate of doing work [Watts = Joules / sec] Intensity = Power / area [Watts / m 2 ] Intensity of blackbody radiation =  T 4 What must be the units of the constant , if T is in Kelvin?  units =

7. Q: What sets Earth’s surface temperature?

8. Venus is closeEarth is intermediateMars is far to the Sundistance from Sunfrom Sun TOO HOTJUST RIGHTTOO COLD Goldilocks Hypothesis: Earth is just the right distance from Sun. (distances not to scale!)

9. Thermal equilibrium: unchanging temperature: Power received from Sun = Power emitted by Earth Power from Sun = Intensity of solar radiation * area of Earth irradiated Intensity of solar radiation = S = 1370 W/m 2 Area of Earth hit by Sun = __________ Power received = radiation * area = S * ________ Q0: What would be Earth’s equilibrium temperature without an atmosphere?

10. Intensity of solar radiation = S = 1370 W/m 2 Greenhouse gases’ radiative forcing ~ 3 W/m 2 Projected increase in our lifetime ~ 1 W/m 2 One xmas tree light per square meter could cause catastrophic warming Note on radiative forcing

11. Power emitted by Earth = Intensity of Earth’s radiation * area of Earth radiating energy Area of Earth radiating = ______ Intensity of Earth’s radiation =  T 4, where the Boltzmann constant  = 5.67 x 10 -8 W/m 2 K 4 Power emitted by Earth = ________________ How much radiation does Earth emit?

12. Simplifying: Radiation emitted = radiation received Power received = power emitted  T 4 = S/4  R 2 Earth S = 4  R 2 Earth  T 4

13.  T 4 = S/4 0. Solve for Goldilocks temperature:

14. Scientific method: Observations and curiosity hypotheses models, quantitative reasoning, and tests improve models bit by bit … 0. Reality check on Goldilocks model: Too cold! (Earth’s average temperature is about 15º C.) Why? What did we leave out?

15. Venus is closeEarth is intermediateMars is far Too hotSTILL TOO HOTToo cold Goldilock Hypothesis is WRONG: What do you predict we will find for the Earth’s equilibrium temperature if we take clouds into account? A warmer or colder planet?

16. Hypothesis 1: Clouds warm Earth Hypothesis 2: Clouds cool Earth Both are partly right…

17. Radiation absorbed by Earth = radiation emitted by Earth Radiation emitted =  T 4 Power absorbed by Earth = Power received from Sun – Power reflected by clouds, … Q1: What would be Earth’s equilibrium temperature with reflective clouds?

18. Radiation reflected = radiation received * (reflectivity, or albedo) = S/4 * (A= albedo) So radiation absorbed = radiation received – radiation reflected = S/4 – S/4 *A = S/4 (1-A) Put it all together: radiation absorbed = radiation emitted S/4 (1-A) =  T 4 To simplify notation in the future, we’ll label the effective solar radiation Earth absorbs: S’ = S/4 (1-A) How much radiation does Earth absorb?

19. 1. Find Earth’s equilibrium temperature with reflective clouds:

20. 1. Reality check on reflective cloud model: The Earth is not really this cold! Its average surface temperature is actually about T = 15º C. What’s missing from this model? Brainstorm ideas, and we will analyze some of them quantitatively.

21. Clouds do not merely reflect and transmit solar radiation – they also absorb Earth’s thermal radiation and re-radiate, especially in longer wavelengths. One-layer model: Assume the atmosphere absorbs all the Earth’s radiation, and re-radiates half of it back down to Earth (and half out to space), at an equilibrium temperature T e. Find Earth’s Surface temperature T s. Q2: What effect do greenhouse gases have on Earth’s equilibrium temperature? http://www.yourdictionary.com/ahd/g/g0258400.html

22. How? Greenhouse gases absorb infrared radiation Kenneth R. Koehler, Raymond Walters College http://www.rwc.uc.edu/koehler/biophys.2ed/dof.html Tohoku University http://www.tagen.tohoku.ac.jp/labo/arima/lecture/spectroscopy/gif/symmode.gif

23. Greenhouse Gases IPCC1 p.38

24. At Earth’s surface,  T s 4 = S’ +  T e 4 radiated by Earth = received from Sun + received from Atmosphere 2. Greenhouse gases re-radiate heat At top of atmosphere, S’ = S(1-A)/4  T e 4

25.  T s 4 = 2 S’ → 2. Find greenhouse effect temperature: Eliminate  T e 4 from the two equations and solve for Earth’s T s : Reality check: This is certainly warmer – in fact it is about 15º C too warm. What’s missing from this improved model? Brainstorm ideas, and we will analyze some of them quantitatively. This is how science progresses – by gradually improving simple models and getting closer and closer approximations to nature’s reality.

26. We found that the Earth is too cold without greenhouse gases, and too warm with them. What’s missing? Two-layer model: The atmosphere actually does not absorb all of Earth’s radiation – it transmits some energy out into space. This imperfect insulator should result in a slightly cooler surface temperature for the planet. We can quantify this effect by saying the atmosphere absorbs a fraction a of the Earth’s radiation (E=  T s 4 ), and transmits the rest (1-a). Meanwhile, the atmosphere continues to radiate with an intensity R=  T e 4. Let’s see how this changes the results of our thermal equilibrium energy balance analysis. Q3: What if the atmosphere also transmits some of Earth’s radiation?

27. Solving any two equations, we find that assuming T s =288K. This means that 23% of Earth’s radiation must be transmitted out into space by the insulating atmosphere, if this two-layer model fully explains why the Earth’s surface temperature currently averages about 288K. What other factors might be involved? Q3: What if the atmosphere also transmits some of Earth’s radiation? (Find a) Top of atmosphere: S’ = R + (1-a)E Earth’s surface: E = S’ + R

28. Q4: What is the effect of ocean and ice albedo on Earth’s global energy balance? We actually included some reflection (r) from the Earth’s surface in our original albedo term (A). Surface albedo is complicated, however, by several factors, including (1) seasonal changes and (2) positive feedback effects.

29. Ice-albedo feedback http://www.bbc.co.uk/portuguese/especial/1126_clima/page4.shtml

30. Feedback systems Positive feedback destabilizes Earth system (bad) Negative feedback stabilizes Earth system (good)

31. Global energy balance: a partial summary

32. Physics is not the whole story! Gaia hypothesis: Biota help regulate Earth’s climate Ex: Faint young Sun Paradox

33. Plankton contribute to absorption and emission of CO 2, cloud formation, ocean albedo, and more. Q5: How do phytoplankton contribute to climate regulation? Coccolithophores under the Scanning Electron Microscopehttp://oceanworld.tamu.edu/NMEA_Talk/

34. Phytoplankton → ocean albedo http://visibleearth.nasa.gov/view_rec.php?id=705 Coccolithophore bloom off the Coast of Britanny: Due to their unusually high reflectivity, “special algorithms have been developed specifically for the remote-sensing detection of coccolithophorid blooms in the ocean. If the data indicates the presence of such a bloom, the data is [flagged to note] this anomalous condition.” http://disc.gsfc.nasa.gov/oceancolor/scifocus/clas sic_scenes/12_classics_blooms.shtml

35. Phytoplankton → atmospheric composition Phytoplankton production is an important sink of atmospheric CO 2. Sinking of phytoplankton biomass below the pycnocline (“biological pump”) removes CO 2 from atmospheric circulation. Biological factors (production, predation, decomposition) and physical/chemical factors (density stratification, acidity of the ocean, wind speed, etc.) affect the efficiency of the biological pump. www.msrc.sunysb.edu/octet/BP_Fig_1.gif www.msrc.sunysb.edu/octet/BP_Fig_1.gif

36. Phytoplankton → sulfur compounds → cloud formation Marine algae produce dimethylsulfoniopropionate (DMSP), which is converted to dimethylsufide (DMS) by phytoplankton and bacterial enzymes during decomposition. DMS then enters the atmosphere where it is photo-oxidized to sulfate aerosols. DMS accounts for 95% of the natural marine input of sulfur gases to the atmosphere, and about 50% of the total global biogenic source of sulfur to the atmosphere. Sulfur compounds act as cloud condensation nuclei. Climate Change Workshops, Zita + Chin-Leo, SORCE, Sept 2006, Orcas Island, WA

37. Solar/atmosphere/ocean/biota interactions

38. SUMMARY

39. In Q0, we found that without an atmosphere, Earth’s equilibrium temperature would be about 279 K, or 9º C too cold. In Q1, we found that an Earth with reflective clouds but no greenhouse gas trapping was about 255 K, or 33º C too cold. In Q2, we found that an Earth with reflective clouds and an insulating layer of greenhouse gas atmosphere was about 15º C too warm. (One-layer model) Two-layer model: If the atmosphere is an imperfect insulator, transmitting about 23% of Earth’s radiation into space, this yields Earth’s observed temperature of 288 K. Positive feedback tends to warm Earth: melting ice decreases albedo; increased water vapor increases greenhouse effect. Negative feedback stabilizes: warmer Earth radiates more. Biota such as plankton also contribute to ocean albedo, atmospheric composition, and cloud formation, all of which have impacts on the global energy balance. SUMMARY

40. References and sources of figures Shindell et al. (http://www.people.virginia.edu/%7Emem6u/ssmrw02.html)http://www.people.virginia.edu/%7Emem6u/ssmrw02.html Robert Stewart (http://oceanworld.tamu.edu/NMEA_Talk/NMEA_Talk_2004.html)http://oceanworld.tamu.edu/NMEA_Talk/NMEA_Talk_2004.html ETE team (http://www.cotf.edu/ete/modules/coralreef/CRatmo.html)http://www.cotf.edu/ete/modules/coralreef/CRatmo.html Judith Lean and David Rind, Sun-Climate Connections: Earth's Response to a Variable Sun, Science, Vol 292, Issue 5515, 234-236 (2001 ) Friis-Christensen, E.Friis-Christensen, E.; Lassen, K., Science, 254, 698-700 (1991)Lassen, K. D. Rind (from J. Lean), The Sun's Role in Climate Variations Science, Vol 296, Issue 5568, 673-677 (2002)

41. The Earth System, Lee R. Kump, James F. Kasting, Robert G. Crane, Ed.2, pub. Pearson/Prentice Hall The Earth Institute, Columbia University (http://www.earth.columbia.edu/news/2005/images/conveyor_belt.gi)http://www.earth.columbia.edu/news/2005/images/conveyor_belt.gi Atelier Changement Climatique, ENPC (http://www.enpc.fr/fr/formations/ecole_virt/trav-eleves/cc/cc0304/cycle-carbone/cycle- carbone.htm)http://www.enpc.fr/fr/formations/ecole_virt/trav-eleves/cc/cc0304/cycle-carbone/cycle- carbone.htm Richard Dewey, UVic, BC (http://web.uvic.ca/~rdewey/eos110/webimages.html)http://web.uvic.ca/~rdewey/eos110/webimages.html Scott Rutherford, Roger Williams Univ., RI, Milankovitch Cycles in Paleoclimate, (http://deschutes.gso.uri.edu/~rutherfo/milankovitch.html)http://deschutes.gso.uri.edu/~rutherfo/milankovitch.html E.J. Zita, solar physics research at Evergreen and HAO/NCAR http://academic.evergreen.edu/z/zita/research.htmhttp://academic.evergreen.edu/z/zita/research.htm, http://www.hao.ucar.edu/