The Earth's Climate

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The Earth's position

The position of the Earth in relation to the Sun changes constantly depending on three parameters:
- The eccentricity of the Earth's orbit varies between 0.005 and 0.05 over a period of 100,000 years. It is currently about 0.016;
- The inclination of the Earth in relation to the ecliptic plane varies between 22 and 25 degrees over a period of 41,000 years. The Earth's inclination is currently about 23.5 degrees;
- The precession of the equinoxes induces a movement of the Earth's axis of rotation around a cone of revolution over a period of 21,000 years.
Variations in these orbital parameters are constantly modifying the Earth's position and exposure to the Sun. However small, these variations, are sufficient to modify the amount of solar energy that reaches the Earth. They have given rise to a theory, called the Milankovitch Astronomical Theory, which explains the major climatic changes our planet has undergone over the past two million years.
Slight orbital variations result in major climatic cycles over periods of 100,000 years. The Earth has experienced a series of long glacial periods, followed by shorter and warmer interglacial periods lasting from 10,000 to 20,000 years. The average temperature difference between these periods is approximately 5 degrees Celsius on the planet's surface.
The interglacial period in which we now live began 11,000 years ago, and could continue for tens of thousands of years.