The Milankovitch Cycles

Introduction

Purpose and Problem

Problem:

  1. Are the Milankovitch cycles and theories surrounding them a valid model and method for prediction of future climate change events?
  2. Because of the huge spans of time involved in the different Milankovitch Cycles (thousands of years) is there a reliable method of colaberating Milankovitch's theories?
  3. Are the Milankovitch Cycles the only major influences over the earths climate? Are there other effects that work in conjunction or are influenced by the Milankovitch Cycles?
  4. Do the Milankovitch Theories only lend themselves to predicting large scale climate change events such as Ice Ages?

Goals:

We will be examining multiple sources of data in an attempt to determine if the Milankovitch Cycles are a valid method for predicting long term climate cycles.

The data the we will be examining includes:

  1. Ice Core measurements, graphing CO2 and CH4
  2. Current Theories Relating the Milankovitch Cycles to Climate Change
  3. Ocean temperatures and currents
  4. Original Milankovitch Models

Milutin Milankovitch

Milutin Milankovitch (1879-1959) is the man responsible for creating theories on global climate change that relate to the long term orbital position of the earth. After engaging in several other carrels, he took up a position teaching applied mathematics at the University of Belgrade. (source)

Milankovitch is best known for the theory that bares his name. The Milankovitch Theory, otherwise known as the astronomical theory of climate change, it is an explanation of the seasonal changes the result changes in the Earths orbit around the Sun. He determined that three three different orbital cycles had influence over the seasons and and the amount of seasonal intensity. Seasonal Intensity refers to the difference between seasons. Increased seasonal intensity would result in cold winters and hot summers.

The Milankovitch Cycles

Milankovitch based his theories of three different orbital cycles. Which can effect the amount of incoming solar radiation, as well as temporal and spatial distribution. (source)

1. Eccentricity: Eccentricity refers to the shape and variation of the Earths orbit around the sun. This term can also be described as orbital wobble. Earths orbit around the sun is not a perfect circle. It is elliptical in nature and this ellipse can vary in strength. "When the orbit is circular, the lengths x and y are equal and e = 0. The Earth's orbit has been found to vary from being near circular (e = 0.005) to markedly elliptical (e = 0.06) with two primary periodicities of approximately 96,000 and 413,000 years." (source) "With maximum eccentricity, differences in solar radiation receipt of about 30% may occur between perihelion and aphelion." (source) Perihelion and Aphelion refer to the position of the earth as related to the sun. When the Earth is at Perihelion it is closest to the sun and with the Earth is at Aphelion is farthest away from the sun.

2. Obliquity: Obliquity refers to the axial tilt of the Earth. The Earth is constantly spinning on its axis, which today is tilted to an angle of 23.4 degrees. Over a period of 41,000 years this the degree of tilt varies between 22 and 24.5 degrees. This tilt influences the Claudia distribution of solar energy. (source) Axial tilt plays an important role in seasonal change, as the tilt of the earth effects the amount of insolation received a higher latitudes.

3. Precession: The third and final variation is called precession. It is the most complex of the three orbital variations. Precession is caused by the gravitational forces exerted on the Earth by all the other planetary body's in our solar system. "Precession has two components: an axial precession, in which the torque of the other planets exerted on the Earth's equatorial bulge causes the rotational axis to gyrate like a spinning top; an elliptical precession, in which the elliptical orbit of the Earth itself rotates about one focus."(source) Precession occurs over a period of 22,000 years. The influence that precession has over the amount of total insolation is very small, however precession does influence the amount of solar received by the Earths hemispheres during winter and summer months.

The Power of Three: How they fit together.

Alone these three different cycles have limited influence over the climate and seasonal change on Earth. Combine the three and complex patterns are formed.

Eccentricity refers the changes in the shape of Earths elliptical orbit. Eccentricity influences the total amount of solar radiation received by the Earth at Aphelion and Perihelion. The effects of Eccentricity on Precession and Obliquity are limited to influencing the amount of solar being distributed by the current rates of Precession and Obliquity. More specifically "If the perihelion occurs in mid-June i.e. when the Northern Hemisphere is tilted toward the Sun, then the receipt of summer solar radiation in Northern Hemisphere will increase. Conversely, if the perihelion occurs in December, the Northern Hemisphere will receive more solar radiation in winter." (source)

Precession and Obliquity are more closely related as they both influence the Earths axis which in turn influences seasonal changes. Obliquity (Axial Tilt) effects the amount of insolation at higher latitudes. "Consequently, variations in the Earth's axial tilt affect the strength of the latitudinal temperature gradient. Increased tilt has the effect of raising the annual receipt of solar energy at high latitudes, with a consequent reduction in the latitudinal temperature gradient." (source)