The desertification occurring from North Africa currently affects southern Portugal, particularly the Algarve region. The author recalls that, in his childhood, rainfall began in early Autumn, followed by intense, pendulum-like, and prolonged rains during Winter, favoring the preparation of fields for plowing.
According to climatologists, the main cause of this desertification is Earth's axial precession, a slow and continuous movement of Earth's axis that describes a "wobble" over thousands of years. This cycle takes about 25,772 years to complete, with the North Pole advancing 1 degree every 71.59 years relative to the Sun's cycle, caused by the gravitational forces of the Moon and the Sun.
Precession is only one of three Milankovitch Cycles. The other two are Eccentricity, which refers to changes in the shape of Earth's orbit between more elliptical and more circular, with a periodicity of about 100,000 years, and Axial Tilt, which varies between approximately 22.1 and 24.5 degrees over 41,000 years, affecting the distribution of solar radiation and the contrast between seasons.
Between 11,000 and 5,000 years ago, the so-called "Green Sahara" was a verdant and populous region, as evidenced by lake sediments, pollen, freshwater shells, and rock paintings. With desertification, vast human migrations occurred to wetter zones such as Mesopotamia and the Nile, influencing the development of Egyptian Civilization. Ancient DNA studies detected signs of African affinity in Iberian samples from the Neolithic and Bronze Age, suggesting migrations across the Strait of Gibraltar to the Iberian Peninsula.
