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, , 1994
Ultimately named “Milankovitch cycles” after Milutin Milankovitch,
Serbian mathematician ( ).
Developed mathematical theory of Earth’s ice ages based on
amount of sunlight Earth receives (published in 1920).

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

4. Eccentricity and the shape of Earth’s Orbit
2b = minor axis
2a = major axis
empty focus
Earth’s e currently > 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* = 2a Eccentricity and the shape of Earth’s Orbit r* r
Aphelion E E
empty focus
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. Calculated the changes in Earth’s orbital parameters during the past.
Milutin Milankovitch
Calculated the changes in Earth’s
orbital parameters during the past.
e = 0.005
Presently e =
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-7

9. All of the Planets in the Solar System are pulling on EarthJ M E V

10. All of the Planets in the Solar System are pulling on EarthJ M E V

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

12. No tilt --> No seasons
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. 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
en.wikipedia.org
Appears
clockwise
when viewed
from above
north pole.
Appears counter-
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. Half a precessional cycle in the past
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. Data to support Milankovitch was a long time coming
Oscillations every
23,000 and 41,000 years
Oscillations every
100,000 years
After Raymo, M.E., Ann. Rev. Earth Plan. Sci. 22, , 1994

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

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

33. ] = ~ 90 - 115,000 years apart Orbital Tuning-- what do you think?
top = 0 yr
] = ~ ,000 years apart
1st reversal = 780,000 yr B.P.
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