Milankovitch cycles
Over long time scales, climate is controlled by Milankovitch cycles changing the amount of solar radiation reaching the earth. The weakening and strengthening of the monsoon also plays an important role. Siroco "et al." suggest that the strength of the monsoon in linked to the albedo in the Himalaya. Cooler temperatures in the northern hemisphere winter lead to more sunlight reflected off snow and ice and weaker summer monsoons, leading to a drier climate in East Africa. The strength of the monsoon is also linked to Milankovitch cycles with a lag of around 8,000 years. Generally the maximum monsoons occur 2,500 years after a glacial minimum. This maximum corresponds to a minimum of sea surface temperatures.