1. Historical Climate Change
Milankovitch Cycle
Historical Climate Change

2. During warm, interglacial periods denoted by the grey bars, the concentrations of greenhouse gases, CO2 and CH4, were higher than during the colder, glacial periods.

4. Earth’s Natural Climate Change
Interglacial periods occur about every 100,000 years.
Why do these glacial and interglacial changes occur?

5. Earth Orbit

6. Eccentricity, Spherical
100,000 years
Max to Max

7. Obliquity, Axial Tilt
Varies from about 22° to 25° Period of about 41,000 years.

8. Precession, Wobble
Precession period of about 20,000 years.

9. Why do times of glaciation occur episodically on Earth?
Large glacial cycles were initiated external to the Earth (exogenic). However, the exogenic changes in solar input are not sufficient to explain the amplitude of the variations, and today’s concerns about climate change are based on changes within earth’s systems (endogenic), particularly the carbon and hydrologic cycles.

10. Milankovich Cycle 3 things change within Earth’s motion
1 - The Eccentricity of the Earth’s orbit varies just slightly from one maximum to the next every 100,000 years.
Eccentricity is at its maximum = Earth is closest to the sun.
2 - The angle of tilt, the obliquity, varies from about 22° to 25° with a period of about 41,000 years.
3 - Like a large wobbly spinning top, the Earth’s rotation axis precesses with a precession period of about 20,000 years.

11. Orbital Forcing About every 100,000 years.
When all 3 variations occur at the same time warming begins.
The end of an ice age coincides with the times when the northern hemisphere
tilts toward sun at high obliquity
the orbital eccentricity is at a maximum
the Earth is closest to the sun during the northern hemisphere summer.

12. So what’s the big deal about climate change? What’s different now?

13. Group Activity
Draw a picture that shows the Earth in orbit and accounts for all aspects of the Milankovitch cycle.
Label the 3 parts and how they can vary.
Indicate on the drawing when an interglacial period is triggered.