Climate of Mount Kenya - Past Climate - Overview

Overview

Mount Kenya was an active volcano in the Pliocene, 2.5-5 million years ago (mya). 5 mya the Mediterranean Sea was dry and the dunes of the Sahara were much further south; the area that is now Kenya was an arid savanna. By 3.7 mya the climate was much wetter than it is at present, and the broad pattern of vegetation in East Africa established, although there would still be much variation in species and altitudinal distribution due to climatic oscillations. 2.5 mya the first of 21 major ice ages in the northern hemisphere during the Quaternary occurred. Tropical Africa experienced much colder temperatures than at present. Ethiopian vegetation belts were lowered and a similar signal would have existed in Kenya. 1 mya drier periods became more pronounced, a trend which loosely continues today.

150 kya was the maximum of the penultimate major glaciation, which was the most extensive of the Pleistocene glaciations. This was followed by the moist Eemian interglacial when temperatures were warmer than present. An arid phase followed, lasting from 100-90 kya with dunes building up in Southern Africa, followed by a short but intense cold stage from 75-58 kya. Near the end of this cold phase the first Heinrich event(H6) occurred, releasing a mass of ice into the north Atlantic 66 kya. This caused cooler temperatures in the northern hemisphere and a cooler Himalaya which probably resulted in a weakening of the monsoon. A series of Heinrich events followed, with an associated drying of the East African climate at 50, 35, 30, 24, 16 and culminating with the Younger Dryas period 12kya.

31-21 kya was a cool dry phase, with vegetation belts lowering. Upper montane forest species occurred where presently lower montane forest species are and there is evidence that montane forest was widespread at lower altitudes. The record from the Congo agrees with this but Lowe and Walker suggest that East Africa was moister than present. This discrepancy may possibly be explained by the difference in location for problems with calibrating the dates.

The Last Glacial Maximum (LGM) occurred 23-14.5 kya with a very arid phase in Africa when desert extended hundreds of kilometres (miles) further south than present. Temperatures were 5-6 °C cooler than present and there was a general rain forest retreat. The summer monsoon during the LGM was very weak. Glacial moraines from near the end of the LGM in East Africa show that the south-easterly monsoon was less wet during the LGM than the current dry north-easterly monsoon.Stratus clouds may have been extensive resulting in a cooling effect but little rain.

By 13.8 kya the climate had moistened and montane forest was again spreading after a minimum during the LGM. The monsoon strengthened again, and lake levels and river activity in East Africa increased. High altitude vegetation was mainly limited by temperatures and not drought, again implying a wet climate.

Before the Younger Dryas temperatures were similar to present but the forest cover incomplete. During the younger Dryas 12.9-11.5 kya brought about by the last Heinrich event, there was a pronounced weakening of the summer monsoon over East Africa, and montane forest retreated and East African lake levels fell. Forests reached the same range and density as present day after the younger Dryas when the climate again became moister.

For the next 5 thousand years, from 10-5 kya, the climate was generally moister than present but oscillations were still present. The monsoon was strong, but there were centuries long weaker periods. leasing to a drier phase, but conditions were still moister than present.

After 5 kya the monsoon began to gradually weaken and the East African climate became similar to present day, but slightly colder and drier. The lake levels in Ethiopia were low from 5.4-2.5 kya as well as in Ghana 4.5-3.2 kya. During these last 5 thousand years, Mount Kenya went through a series of minor glacial advances. There was a temperature minimum over 3.7-2.5 kya and also during the little ice age spanning the years 1300-1900 when a permafrost regime dominated on Mount Kenya.