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Climatological Cycles & Green House Affects

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					Did Humans Stop an Ice Age? 8000 years of global warming
Scientific American, March 2005 Pages 46-53 Basic Premis: Human activities such as farming and forest management may have modified prehistoric climate more than previously suspected

Climatological Cycles and Green House Affects
By Dan Vasicek 3/25/2005

Outline
• Basic Idea – Prehistoric man burned forests, made gardens, and released CO2 that prevented an Ice Age that should have started 8000 years ago • References • Background - Discussion of cycles that affect climate • Ruddimann article in Scientific American

References
• “How Did Humans First Alter Global Climate?”, William Ruddiman, Scientific American, March 2005, • “A test of the overdue-glaciation Hypothesis”, William Ruddiman, Stephen Vavrus, John Kutzbach, Quaternary Science Reviews 24, (2005) 1-10 • Earth's climate: past and future / William F. Ruddiman, New York : W.H. Freeman, c2001, 465 pages

Link to the 2005 QSR paper
• http://www.sciencedirect.com/science?_ob =MImg&_imagekey=B6VBC-4DTK6RV-1F&_cdi=5923&_user=10&_orig=browse&_ coverDate=01%2F01%2F2005&_sk=9997 59998&view=c&wchp=dGLbVtbzSkzV&md5=d06dae2e30dceb90f2f0f1ecc e60102d&ie=/sdarticle.pdf

Milankovitch cycles: climate variations caused by orbital effects
• Winter/Summer  Axis of rotation inclined 23.4 degrees to the ecliptic (1 year cycle) • Elliptical orbit (3%), Perhelion shifts 25 minutes per year (365*24*60/25=21,000 year cycle) • Obliquity variation 23.4+-1 degrees 41,000 years period • Eccentricity of the orbit varies periodically with period ~100,000 years (0 9%)

Annual Seasons ( 1 yr)

Summer

Winter

Elliptical Orbit vs Seaons (21,000 yrs)
Winter

perhelion

Summer

Obliquity Variation 41,000 yrs
22.4

24.4

41,000 year cycle

Eccentricity variation 100,000 yrs
e =0- 9%

Milankovitch cycles: Effect on earthly incident solar energy
• Obliquity variation
– Increases difference between Winter and Summer hemispheres – No net effect on average annual solar energy

• Elliptical orbit
– Solar intensity varies as 1/r2 – Therefore intensity changes by 2*e) – 0 18% as ellipticity changes from 0-9% – No net effect on average annual solar energy

Elliptical orbit net affect on yearly energy
r ( )  h /
2

1  e cos(  )
2

Equation of an Ellipse

E  C 1  1 / r dt dt 

Total Solar Energy per year

1  e cos(  ) 
C 1c 2 h 
4 2

c2d

2

Constant Angular momentum

E  E e



d 

C 1c 2 h 
4 2

2
Energy is not a function of ellipticity

0

Milankovich Cycles cannot, by themselves, cause ice ages
• Modify the difference between Summer and Winter • They do not modify the average total solar energy incident on the earth • Most land mass is in the northern hemisphere

Evidence for Paleolithic Climate Modification
• Significant evidence for Agriculture 11,000 years ago
– Paleolithic Sickle blades – Pollen from cultivated plants – Genetic evidence

• Forest management practices
– Burning forest
• Improve grazing • Easier hunting • Grow crops

– Indians burned the forest 2 times a year

Coincidence between the Orbital cycles and Methane concentration
By permission of William Ruddiman

Coincidence between CO2 concentration and variation of the eccentricity of Earth’s orbit
By Permission of William Rudiman

Departure from the expected trend: Human Intervention?

By permission of William Ruddiman

Testing the Hypothesis
• Ruddiman experimented with the GENISIS climate model • Reported in:
– Quaternary Science Reviews 24, (2005) 1-10

• Result of the model: Overdue Glaciation confirmed

More tests of the Hypothesis
• Plagues correlate with decreases in CO2

By permission of William Ruddiman

By permission of William Rudiman Temperature

Comparison of Effects


				
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