The Great Sahara Desert
Some say that the Sahara desert before the first glacial period was much larger, and some assert that the Sahara desert appeared 4000 years ago. For example, German scientists using computer modeling the Earth's climate, and found that the Sahara became a desert 4000 years ago. 10,000 years ago, the largest desert in the world was covered with grass and low bushes, but then the summer was hotter and the rain almost stopped. Of course, disappeared many ancient civilizations, and all life has left the Sahara. According to scientists from the Potsdam Institute for Climate Research, the transformation of the Sahara desert has become one of the most dramatic climatic events on Earth foreseeable millennia. Why is it so unstable climate? It turns out that the axis tilt of the Earth to the Sun is gradually changing: Approximately 9,000 years ago it was 24.14 degrees, but now - 23.45 degrees. Today, the Earth most closely approaches the Sun in January, ten thousand years ago the same - at the end of July. Subtle changes in Earth's orbit around the Sun, increased interaction with the atmosphere, ocean and land, climate change beyond recognition.
In the northern zone of precipitation in winter and their number does not exceed 200 mm per year. To the south of their number decreases, and in the central zone they fall out occasionally. The average value of less than 20 mm. Sometimes 2-3 years of rainfall does not fall out. However, in such areas may unexpectedly get heavy rains, causing severe flooding. Aridity of the Sahara and the changes in the latitudinal direction, from west to east. On the Atlantic coast of rainfall does not fall, because rare westerly winds cooled passing along the coast of the Canary Current. There are frequent fogs. On the tops of mountain ridges and highlands rainfall increases slightly due to condensation of water vapor. Sahara features a high degree of volatility. Its total annual value changes from 2500 to 5500 mm, which is more than 70 times the amount of precipitation.