IB Environmental systems and societies 6.1E Milankovitch Cycles Notes

Orbital Cycles That Drive the Ice Ages

1. Milankovitch cycles are long-term, predictable variations in Earth's movement and orientation in space.
2. They alter how much solar radiation (insolation) reaches Earth and how it is spread across latitudes and seasons.
3. They operate over tens to hundreds of thousands of years, driving natural shifts between glacial and interglacial periods.
4. There are three primary cycles:
   1. eccentricity (shape of Earth's orbit),
   2. obliquity (axial tilt),
   3. precession (axial wobble).
5. Together they change Earth's energy budget, influencing ice-sheet growth, CO₂ concentrations, and global climate.

Eccentricity: The Shape of Earth's Orbit

1. Earth's orbit shifts between more circular and more elliptical shapes.
2. This cycle lasts about 100,000 years.
3. When the orbit is more elliptical, Earth's distance from the Sun varies more across the year.
4. This widens the gap between the closest point (perihelion) and farthest point (aphelion), increasing seasonal variation in insolation.
5. When the orbit is more circular, radiation is spread more evenly through the year.

Climate Impacts of Eccentricity

1. A more elliptical orbit intensifies seasonal contrasts, especially in the Northern Hemisphere.
2. A more circular orbit reduces seasonal differences, letting ice sheets grow if other conditions also favour cooling.
3. When low eccentricity aligns with low tilt and certain precession conditions, glaciers expand over thousands of years.
4. During the last glacial maximum (about 20,000 years ago), Earth's orbit was near-circular, reinforcing long-term cooling.

Obliquity: The Tilt of Earth's Axis