Milankovitch cycles

Milankovitch cycles describe how Earth's movements change our climate over thousands of years. These cycles are named after Milutin Milanković. He was a Serbian geophysicist and astronomer. In the 1920s, he provided a detailed analysis of these patterns. He showed how changes in Earth's orbit affect solar radiation. Solar radiation is the sunlight that reaches the Earth's surface. This process is known as solar forcing.

Earth's movements change because of gravity from other bodies in the Solar System. The gravitational pull of planets like Jupiter and Saturn affects our orbit. These interactions cause three main changes: eccentricity, obliquity, and precession. Eccentricity is the shape of Earth's orbit. Obliquity is the angle of Earth's axial tilt. Axial precession is the wobble of Earth's axis.

Orbital eccentricity measures how much our orbit departs from a perfect circle. Our orbit is an ellipse, which is an oval shape. The eccentricity can vary between nearly circular and mildly elliptical. The highest eccentricity in the last 250 million years was 0.0679. When the orbit is more elliptical, the distance to the Sun changes more. This causes a larger variation in solar radiation throughout the year.

Eccentricity changes follow specific mathematical cycles. A major component occurs every 405,000 years. There are also cycles of 95,000 and 124,000 years. These combine into a 100,000-year cycle. The current eccentricity is 0.0167 and it is decreasing. As the orbit becomes more circular, the seasons will become more similar in length. This happens because the difference between perihelion and aphelion decreases.

Obliquity refers to the tilt of Earth's axis relative to its orbital plane. This tilt varies between 22.1 and 24.5 degrees. This variation follows a cycle of about 41,000 years. The current tilt is 23.446 degrees. A greater tilt makes the seasons more extreme. It provides more radiation to the summer hemisphere and less to the winter hemisphere.

Axial precession is the change in the direction our axis points toward the stars. This motion happens every 25,700 years. It is caused by tidal forces from the Sun and the Moon. Apsidal precession also occurs as the entire elliptical orbit rotates in space. This rotation takes about 112,000 years. Together, these movements change when Earth is closest to the Sun. The closest point is called perihelion. The furthest point is called aphelion.

These cycles have a massive impact on global temperatures. Milanković focused on the 65° north latitude. This area has a large amount of land. Land masses change temperature much faster than oceans. Oceans have high thermal inertia, which means they resist temperature changes. This delay happens because convective mixing keeps deep waters cooler. These cycles can influence the start of glacial periods.

Currently, perihelion occurs around January 3. This means the Earth is moving fastest during the northern hemisphere's winter. Because of Kepler's second law, the Earth spends less time near perihelion. This makes northern winters and autumns shorter. In the southern hemisphere, the effects are reversed. In about 13,000 years, the north pole will tilt toward the Sun during perihelion. This will create much more extreme seasonal variations in the northern hemisphere.