Name:   MAJ USA RET - Subject:   Simpler explanation Date:   10/14/2022 10:40:15 AM (updated 10/14/2022 10:42:51 AM)

We scientists wish that the science of climate change was more intuitively obvious. But, it doesn't fit well into a 30 second sound bite.

The Milankovic cycles explained in a simple format:

https://www.youtube.com/watch?v=wi-VEby3m9E  (5 minute video) 

Eccentricity - The Earth orbits the sun in an oval shape called an ellipse, with the sun at one of the two focal points (foci). Ellipticity is a measure of the shape of the oval.

The Earth's orbit slightly changes its eccentricity over the course of 100,000 years from nearly 0 to 0.07 and back again. When the Earth's orbit has a higher eccentricity, the planet's surface receives 20 to 30 percent more solar radiation when it's at perihelion (the shortest distance between the Earth and sun each orbit) than when it is at aphelion (the largest distance between the Earth and sun each orbit). Today, the eccentricity of Earth's orbit is 0.017. At perihelion, which occurs on or around Jan. 3 each year, Earth's surface receives about 6 percent more solar radiation than at aphelion, which occurs on or around July 4.

Axial tilt - The tilt of the Earth's axis relative to the plane of its orbit is the reason that we experience seasons. Slight changes in the tilt changes the amount of solar radiation falling on certain locations of Earth. Over the course of about 41,000 years, the tilt of the Earth's axis, also known as obliquity, varies between 21.5 and 24.5 degrees.

When the axis is at its minimal tilt, the amount of solar radiation doesn't change much between summer and winter for much of Earth's surface and therefore, seasons are less severe. This means that summer at the poles is cooler, which allows snow and ice to persist through summer and into winter, eventually building up into enormous ice sheets.

Today, the Earth is tilted 23.5 degrees, and slowly decreasing. With respect to axial tilt, we are proceeding toward conditions favorable for the onset of the next ice age.

Precession - Earth wobbles just slightly as it spins on its axis, similarly to when a spinning top begins to slow down. The wobble doesn't change the tilt of Earth's axis, but the orientation changes. Over about 26,000 years, Earth wobbles around in a complete circle.

As the Earth completes a precession cycle, the orientation of the planet is altered with respect to perihelion and aphelion. If a hemisphere is pointed toward the sun during perihelion (shortest distance between Earth and sun), it will be pointed away during aphelion (largest distance between Earth and sun), and the opposite is true for the other hemisphere. The hemisphere that's pointed toward the sun during perihelion and away during aphelion experiences more extreme seasonal contrasts than the other hemisphere.

Currently, the southern hemisphere's summer occurs near perihelion and winter near aphelion, which means that (e.g.) Australia experiences more extreme seasons than Siberia.

https://www.livescience.com/64813-milankovitch-cycles.html

These cycles repeat themselves… and sometimes they come together for a maximum effect. And sometimes they diverge for a milder effect.

Milankovic calculated that Ice Ages occur approximately every 41,000 years. Subsequent research confirms that they did occur at 41,000-year intervals between one and three million years ago. But about 800,000 years ago, the cycle of Ice Ages lengthened to 100,000 years, matching Earth’s eccentricity cycle. While various theories have been proposed to explain this transition, scientists do not yet have a clear answer.