Did Humans Stop an Ice Age 8000 years

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 CO 2 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, c 2001, 465 pages

Link to the 2005 QSR paper • http: //www. sciencedirect. com/science? _ob =MImg&_imagekey=B 6 VBC-4 DTK 6 RV-1 F&_cdi=5923&_user=10&_orig=browse&_ cover. Date=01%2 F 2005&_sk=9997 59998&view=c&wchp=d. GLb. Vtbz. Skz. V&md 5=d 06 dae 2 e 30 dceb 90 f 2 f 0 f 1 ecc e 60102 d&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/r 2 – 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 Equation of an Ellipse Total Solar Energy per year Constant Angular momentum Energy is not a function of ellipticity

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

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

By Permission of William Rudiman Coincidence between CO 2 concentration and variation of the eccentricity of Earth’s orbit

By permission of William Ruddiman Departure from the expected trend: Human Intervention?

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 CO 2

By permission of William Ruddiman

Temperature By permission of William Rudiman Comparison of Effects