The shift from a lush, green Sahara to the arid conditions in northern Africa today, approximately 5.5 thousand years ago, represents a significant environmental transformation that profoundly impacted human societies. This transition, known as the African Humid Period (AHP), is a compelling example of how rapidly and extensively climate change can influence human communities. Researchers have identified this transition as a clear instance of climate tipping points, where minor disturbances trigger a significant, non-linear response in the climate system, leading to a shift to a different future state with significant consequences for the biosphere.

In a recent study published in Nature Communications, climate researchers identified two main types of tipping points. The first type involves processes slowing at an increasing rate, making it challenging for the climate to recover from disturbances until a transition occurs. The second type is characterized by a flickering between stable humid and dry climates shortly before the transition. Understanding these tipping points and their early warning signals is crucial for predicting future climate tipping points caused by human activities.

The research, led by Martin Trauth and colleagues from the Universities of Cologne, Aberystwyth, and Addis Ababa, involved the analysis of lake sediments obtained through scientific deep drilling in the Chew Bahir Basin, a former freshwater lake in eastern Africa. By evaluating drill cores that can reconstruct the region’s past 620,000 years of climate history, the team observed 14 dry events, each lasting 20-80 years and recurring at intervals of approximately 160 years, marking the end of the AHP. During the transitional phase, seven wet events occurred alongside the dry events, indicating a high-frequency, extreme wet-dry climate “flickering” characteristic of the region.

The study’s findings suggest that transitions with flickering are a defining feature of the region, as evidenced by similar transitions found in older sections of the sediment cores. Notably, the research also challenges the notion of human activity leading to an accelerated end of the AHP, as some researchers proposed, emphasizing the transition’s natural occurrence when human influence on the environment was minimal. The impact of this climate tipping on human societies is evident in the traces of settlement in the Nile valley at the end of the African Humid Period, attracting millions of tourists to the region annually.

This study illuminates the complex interplay between climate transitions, human adaptation, and the environmental history of northern Africa, providing valuable insights into the region’s climatic dynamics and the resilience of human societies in the face of significant environmental changes.

References

• Trauth, M. H., Asrat, A., Fischer, M. L., Hopcroft, P. O., Foerster, V., Kaboth-Bahr, S., Kindermann, K., Lamb, H. F., Marwan, N., Maslin, M. A., Schaebitz, F., & Valdes, P. J. (2024). Early warning signals of the termination of the African Humid Period(s). Nature Communications, 15(1), 3697. https://doi.org/10.1038/s41467-024-47921-1
• University of Potsdam. (2024, May 7). Study identifies early warning signals for the end of the African humid period. Phys.Org; Phys.org. https://phys.org/news/2024-05-early-african-humid-period.html