Six ice cores from Kilimanjaro were used to show climate change in the Holocene in eastern equatorial Africa from roundabouts 11.7 thousand years ago. In analyzing the ice cores, it was discovered that there were 3 periods of abrupt climate change during the Holocene, and the last one happened to coincide with the "First Dark Age," or the greatest recorded drought in tropical Africa. What's amazing is that the longest cores that were drilled were only about 50 meters long, yet they held thousands of years of history within them.
Isotopic enrichment indicates warmer conditions, and reduced concentrations of major aerosol species (Mg2+, Ca2+, SO4 2–, and NO3 –) indicates wetter conditions, and these were prevalent from about 11 to 4 ka. So, there was still ice being formed during the African Humid Period, which occurred during this time and with these conditions. Then, at about 6.5 ka, there was an abrupt 18O depletion in the ice records, which indicates a cooling event. This could have altered the environment significantly (which makes sense). The third abrupt event is seen by a dust layer within the ice, which appears to have been deposited at a very dry period in time. (This supports the reference to the drought, or the "First Dark Age").
This has been such an interesting resource to study climate change; however, if the current climate change continues, this ice will most likely melt and we will lose this tool to analyze history.