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Lecture 39

EARTHSC 1G03 Lecture 39: EARTHSC 1G03 - Lecture 39 (Global Change)

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Earth Sciences
Maureen Padden

EARTHSC 1G03 Lecture 39: Global Change Variation in Global Geometry – Milankovich Theory 1. Eccentricity of Orbit o Periodically, Earth orbit goes from circular to elliptical on a 100 000 year cycle. o At high eccentricity, Earth can be periodically far away from the sun. o The colder seasons would allow ice to form, leading to cycle of glaciation. 2. Tilt of Earth Axis o The angle of tilt varies from 25.5º to 24.5º on a 41 000 year cycle. o At small angles of tilt, less sunlight reaches poles in summer • This could lead to persistence of winter ice through the summer 3. Precession of Wobble of Axis o Precession, or “wobbling” or Earth axis is on a 23 000 year cycle o Affects sunlight input Overall Change in Solar Input ➢ Periodically, precession, tilt, and eccentricity reinforce each other, leading to cyclic variation in heat input from the sun. ➢ Low periods correspond to glaciations. Peaks in cycles are about 100 000 years. Long-term Changes vs. Short-term Changes ➢ Long-term Changes o Ice ages happen throughout Earth’s history, but are rare o Triggers: ▪ Continent over poles ▪ Continent over hot spots, rise in elevation • Higher altitude = colder temperature ▪ Slower mid-ocean ridge spreading – more space in ocean, fewer shallo
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