April 13 - 27, 2005

1. April 13 - 27, 2005 • NOTE: Reviews will be handed back Thurs/Fri to • mailboxes, fax, etc. • Midterms handed back next week. • Searching for periods and patterns in climate records: • Geometry of Earth’s orbit • Astronomical control of solar radiation • Periods and patterns as chronometers • Astronomical control of monsoons, ice sheets, • El Niño, GHGs • Ice cores as climate recorders

2. In addition to long-term trends, Zachos found regularly-spaced warm-cold alternations After Raymo, M.E., Ann. Rev. Earth Plan. Sci. 22, 353-383, 1994 Ultimately named “Milankovitch cycles” after Milutin Milankovitch, Serbian mathematician (1879 - 1958). Developed mathematical theory of Earth’s ice ages based on amount of sunlight Earth receives (published in 1920).

3. N night View of Sun and Earth from above the North Pole day

4. 2a = major axis empty focus 2b = minor axis Eccentricity and the shape of Earth’s Orbit E Earth’s e currently 0.017 --> nearly circular Maximum e = 0.06 Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-6

5. r r* E E empty focus Eccentricity and the shape of Earth’s Orbit E Aphelion Perihelion r + r* = 2a What happens to the solar flux at perihelion and aphelion? Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-6

6. Where are Northern Hemisphere Summer and Winter located?

7. Shape of Earth’s Orbit Today Equinox: length of night and day are equal. Solstice: longest and shortest days of the year Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-2

8. e = 0.005 Milutin Milankovitch Calculated the changes in Earth’s orbital parameters during the past. Presently e = 0.0167 Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-7

9. J E V M S All of the Planets in the Solar System are pulling on Earth

10. J E V M S All of the Planets in the Solar System are pulling on Earth

11. Sun’s equator Jupiter Venus Mercury Earth Mars Ecliptic Obliquity and the Eclipitc Earth is not “straight up and down” with respect to the ecliptic.

12. Obliquity- Earth’s tilted rotation axis Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-3a No tilt --> No seasons

13. Obliquity- Earth’s tilted rotation axis Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-1

14. Obliquity- Earth’s tilted rotation axis • Northern Hemisphere Winter: • occurs at perihelion • tilted AWAY from Sun • winter radiation higher than • for circular orbit At present • Southern Hemisphere Summer: • occurs at perihelion • tilted TOWARDS Sun • summer radiation higher than • for circular orbit Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-5

15. Obliquity- Earth’s tilted rotation axis • Northern Hemisphere Summer: • occurs at aphelion • tilted towards Sun • summer radiation lower than • for circular orbit • Southern Hemisphere Winter: • occurs at aphelion • tilted away from Sun • winter radiation lower than • for circular orbit Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-5

16. Obliquity- Earth’s tilted rotation axis At present Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-13 • Northern Hemisphere Summer: • occurs at aphelion • tilted towards Sun • summer radiation lower than • for circular orbit • Northern Hemisphere Winter: • occurs at perihelion • tilted AWAY from Sun • winter radiation higher than • for circular orbit At present, northern summers and winters are both milder than they could be. Low seasonal contrast.

17. Obliquity- Earth’s tilted rotation axis Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-13 • Southern Hemisphere Summer: • occurs at perihelion • tilted TOWARDS Sun • summer radiation higher than • for circular orbit • Southern Hemisphere Winter: • occurs at aphelion • tilted away from Sun • winter radiation lower than • for circular orbit At present, southern summers and winters are both extreme. High seasonal contrast.

18. Obliquity- Earth’s tilted rotation axis Earth’s obliquity varies from ~22 to 24.5˚ with a period of 41,000 years. Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-4

19. Wobble- Precession of Earth’s rotation axis Wobble = DIRECTION in which spin axis leans Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-8

20. en.wikipedia.org Wobble- Precession of Earth’s rotation axis • Earth’s rotation axis sweeps • out a circle every 27,500 years. • Right now, axis points at • Polaris (North Star) • ~2000 B.C.. Alphas Draconis • was pole star • ~ 14,000 A.D. Vega will be • pole star Appears clockwise when viewed from above north pole. Appears counter- clockwise when starts viewed from Earth. Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-9

21. Precession of Earth’s orbit Elliptical shape of Earth’s orbit is rotating,

22. Precession of Earth’s orbit Elliptical shape of Earth’s orbit is rotating

23. Precession of Earth’s orbit Elliptical shape of Earth’s orbit is rotating Appears counter-clockwise when viewed from above Earth’s North pole

24. Precession of Earth’s orbit Elliptical shape of Earth’s orbit is rotating Appears clockwise when viewed from above North pole Wobble and precession of ellipse IN OPPOSITE DIRECTIONS. Combined effect: 23,000 years to make a full cycle. Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-9

25. Equinoxes and solstices move around the ellipse Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-2

26. Effect of Precession on sunlight received 0.5 Myr 0.5 Myr Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-14

27. Today Half a precessional cycle in the past • Summer at perihelion • LOTS of solar radiation • Winter at aphelion • Minimal solar radiation Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-13

28. Insolation changes with latitude AND season through time Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-16

29. Does all this affect Earth’s climate? Critics said: effect exceeds the cause. 1.3 W/m2 0.1 % Incoming Flux W/m2 Redrawn from Frolich and Lean, 1998 Calendar Year AD

30. Oscillations every 23,000 and 41,000 years Oscillations every 100,000 years After Raymo, M.E., Ann. Rev. Earth Plan. Sci. 22, 353-383, 1994 Data to support Milankovitch was a long time coming

31. 450,000 year record of CO2 from Vostok Ice Core, Antarctica Data generously made available online by the Vostok Ice Core group,

32. N R R N Normal Reverse Orbital Tuning-- what do you think?

33. top = 0 yr 1st reversal = 780,000 yr B.P. Orbital Tuning-- what do you think? ] = ~ 90 - 115,000 years apart Orbital tuning: 1. Apply magnetostratigraphy 2. Assign wiggles to be spaced 100,000 years 3. Match peaks and troughs to insolation curve

34. Orbital Tuning in the Vostok ice core Generously made available online at http://www.usgcrp.gov/usgcrp/images/Vostok.jpg