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Physics of Planetary Climate

Cors221: Physics in Everyday Life Fall 2010 Module 3. Lecture 5: Medium-Term Climate History: The Ice Ages. Physics of Planetary Climate. From Last Time. Long-term (> 10s of millions of years to 4.6Gyr) climate history information can come from geology.

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Physics of Planetary Climate

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  1. Cors221: Physics in Everyday Life Fall 2010 Module 3 Lecture 5: Medium-Term Climate History: The Ice Ages Physics of Planetary Climate

  2. From Last Time • Long-term (> 10s of millions of years to 4.6Gyr) climate history information can come from geology. • Oxygen isotopes (18O) from carbonate (CaCO3) can be used as a paleotemperature proxy. • Can also use similar techniques to measure ancient carbon dioxide levels. • Earth has only had polar ice for ~15% of its history; frequently there is sufficient equator-to-pole heat transport to allow palm trees at the poles. • Specific example: Snowball Earth, when Earth froze over 600 Myr ago. • Snowball Earths are reversed by build up of carbon dioxide, and are followed by global hothouses when the ice melts. • Earth’s climate history is a total roller coaster on 10 million year to billion year timescales.

  3. Climate Since the Dinosaurs

  4. Climate Over the Past 5 Myr

  5. Climate Over the Past 450 kyr

  6. Glaciated Earth

  7. Glaciers and Sea Level Change

  8. Antarctic Drill Cores

  9. From Last Time

  10. Eccentricity Varies on ~100,000 year timescales

  11. Obliquity Varies on ~41,000 year timescales

  12. Longitude of Periapsis Varies on ~23,000 year timescales

  13. Net Solar Flux at 65N

  14. Glacial-Interglacial Cycles

  15. MilankovicCycles

  16. Key Points • Earth was hot in the Eocene 50Myr ago (+12 K or +21F), but Antarctica glaciated over 13 Myr ago and stayed that way. • For the past 2.5 Myr, Earth has been in an Ice Age, characterized by semiperiodic glacial and interglacial cycles with ~100,000 yr period. • With so much of Earth's water bound up in 2-mile-thick glaciers over North America and Siberia, global sea level was 120 m lower. • Earth’s orbital eccentricity, a measure of how far the orbit is from non-circular, changes from 0.0 to 0.05 on 100,000 year timescales (presently 0.017) and 400,000 year timescales. • Earth's obliquity, the angle of tilt of the rotation axis, changes from 22.1 to 24.5 degrees on 41,000 year timescales (presently 23.44). • Day of summer solstice relative to periapsis varies on 21,000 & 26,000 year timescales. • The natural variations in climate over the past 2.5 Myr, i.e. during the ice age, are well-explained by changes in insolation due to orbit and obliquity changes. These are known as Milankovich cycles.

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