Climate of Mount Kenya - Past Climate

Past Climate

Past climate is interpreted using a number of methods including lake levels, river strength, dune systems, glacial extent and pollen. The further back in time one goes, the broader the signals used become. While the climate can be inferred for a specific location 20,000 years ago, 5 million years ago the climate over most of Africa has to be considered and the results adjusted using current analogies. Problems associated with going back a long time include an uneven distribution of records and a shortage of vegetation fossils due to unfavourable conditions.

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.

Since the start of the Quaternary period the northern hemisphere has undergone 21 major ice ages and this signal is also present in East Africa. The past climate of Kenya echos the climatic signal in Europe, entering and leaving cold phases at the same time. During the last glacial maximum, 20,000 years ago, the European Ice Sheet would have diverted the Atlantic weather systems over Kenya. This would have resulted in Kenya having a similar climate to present day Europe. Over the past 6,000 years Mount Kenya has had a series of at least six minor glacial advances as well, with the final maximum at the end of the little ice age in 1900.

The fact that the East African climate was much colder generally can be seen by looking at the other mountains such as Mt Kilimanjaro, Mt Ruwenzori and Mt Elgon. They are all isolated pockets of similar alpine ecosystems with similar with similar fauna and flora. This means that this ecosystem must have been widespread at low altitude for it to reach all these mountains. There still must have been pockets of current lowland ecosystem surviving as otherwise animals which are part of these systems would be extinct. An alternate explanation is that given the timescale of millions of years, the probability of tornados transporting flora and fauna between mountains is high.