The Shrinking and Growing Sahara Desert: Trends, Causes, and Future Projections
The Sahara Desert, the largest hot desert in the world, often faces discussion around its expansion, yet recent evidence suggests a more complex scenario. While the desert has been growing, there are indications that certain conditions could lead to its shrinking. Understanding the trends and causes behind these changes is crucial for both the environment and human communities that rely on the region.
Trends in Rainfall and Vegetation
Recent years have seen an interesting shift in the West African Monsoon, particularly in mid-August and September 2023. While rainfall has been creeping northward, it is not yet leading to significant changes in the landscape. However, scientist believe that if this trend continues, it could lead to the transformation of some parts of the Sahara Desert into tropical thornscrub and tropical dry forest, provided land management practices improve. Overgrazing, however, could exacerbate these changes, leading to increased erosion and further desertification.
The Sahara Desert has been growing by an estimated 10% in the last century due to a 10% decrease in annual rainfall. This trend is not expected to stop for some time due to the current phase of climate cycles. Historically, the Sahara has had phases of green grasslands and lakes, but these were temporary. The transition from a humid period to a desert took place around 5500 years ago, and it has remained a desert ever since, thanks to a sudden cooling during the Holocene Climate Optimum.
Historical Context of Climate Cycles
The humid period in the Sahara, which began around 14600-14500 years ago, coincided with significant environmental changes, including the formation of rivers and lakes and the retreat of the Sahara. This period was followed by two major dry fluctuations during the Younger Dryas and the 8.2 kiloyear event, eventually leading to the end of the African Humid Period around 6000-5000 years ago. The Piora Oscillation, a cold and wet period, further influenced the climate, while the Atlantic period represented the warmest and most humid phase of the Holocene.
Linking Past and Future
The study of past climate cycles provides insights into the potential future scenarios for the Sahara. Many scientists attribute the recent changes to Earth's orbital procession, which has a roughly 25,000 to 26,000-year cycle. The last interglacial warming period also saw significant greening of the Sahara, beyond what was observed during the African Humid Period. It is these orbital changes that are likely to influence future rainfall patterns in the region.
Based on future projections, the Sahara Desert is expected to become wetter as the Earth continues to warm. Climate models, such as the CMIP5 Coupled Model Inter-comparison Project Phase 5, predict increased rainfall in the central and eastern Sahel, while the western Sahel is likely to experience reduced rainfall. This shift is expected to cause a delay in the monsoon's seasonal cycle and lead to a stronger monsoon overall. Enhanced warming of the Northern Hemisphere extratropics compared to the tropics is the primary factor expected to influence these changes.
Conclusion
The Sahara Desert's intricate relationship with climate change, including both its growth and potential shrinkage, highlights the importance of understanding past environmental cycles and current trends. As the Earth continues to warm, the future of the Sahara is likely to be influenced by these natural cycles, with the potential for significant changes in the coming decades. Further research and continued monitoring will be essential for predicting and managing these changes.
References
1. Climate models and projections for the Sahel: [Source link]
2. Changes in rainfall patterns: [Source link]
3. Orbital procession and climate cycles: [Source link]