Unveiling the Sahara’s Hidden History: Epochs of Verdancy Amid Aridity

Recent research discloses that episodes of humidity in North Africa, which converted the Sahara Desert into a verdant landscape, were triggered by the Earth’s orbital precession around the Sun and were inhibited during glacial epochs. Utilizing an innovative climate simulation model, this study furthers the comprehension of such humid intervals and their consequential environmental transformations in the Sahara region.

The groundbreaking research provides novel perspectives on the wet phases that North Africa has experienced over the past 800,000 years, delineating the periodic shifts to a greener Sahara.

This research, recently disseminated in the academic journal Nature Communications, elucidates that these intermittent periods of Saharan moisture were governed by Earth’s orbital dynamics relative to the Sun and were impeded during periods of glaciation.

For the inaugural time, climatologists have modeled the historical instances of the Sahara’s ‘greening,’ presenting empirical data that demonstrates the timing and severity of these wet episodes were also remotely influenced by the impact of extensive, far-removed ice sheets in the Northern Hemisphere.

The principal researcher, Dr. Edward Armstrong from the University of Helsinki and the University of Bristol, articulated: “The cyclical conversion of the Sahara Desert into ecosystems of savannah and woodland stands as one of Earth’s most striking environmental alterations.”

“Our investigation ranks among the pioneering climate simulation studies to represent the African Humid Periods with a magnitude comparable to what paleoclimate records suggest, thereby elucidating the circumstances and temporal occurrence of these phenomena.”

There exists abundant evidence indicating that the Sahara had experienced vegetative states in its history, complete with flourishing rivers, lakes, and fauna dependent on water such as hippos, before its current desert state. These North African Humid Periods could have been pivotal in forming vegetated pathways out of Africa, facilitating the migration of diverse species, including early Homo sapiens, globally.

These so-called ‘greening episodes’ are believed to be spurred by changes in Earth’s orbital attributes, specifically its orbital precession. Precession is the phenomenon wherein Earth experiences an axial wobble, affecting seasonality over an approximate cycle of 21,000 years. This axial movement modulates the quantity of solar energy Earth receives seasonally, thereby controlling the potency of the African Monsoon system and the extension of vegetation throughout this expansive region.

A significant impediment to understanding these phenomena is that most existing climate models have failed to accurately simulate the magnitude of these humid periods, leaving their precise causative mechanisms ambiguous.

The research employed a newly formulated climate model to simulate the North African Humid Periods, significantly enriching the understanding of the factors instigating them.

The study’s findings corroborate that the North African Humid Periods transpired every 21,000 years, dictated by Earth’s orbital precession. This led to warmer Northern Hemisphere summers, amplifying the West African Monsoon system and consequently increasing precipitation in the Sahara, thereby promoting the proliferation of savannah-like vegetation across the region.

Furthermore, the study ascertains that these humid periods were curtailed during glacial epochs when enormous ice sheets blanketed a majority of the high latitudes. These ice expanses had a cooling effect on the atmosphere, stifling the African Monsoon system’s potential to expand. This observation underscores a major climatic interrelationship between these distant geographical zones, which might have hindered the migration of various species, including humans, from Africa during these glacial times in the last 800,000 years.

Co-author Paul Valdes, a Professor of Physical Geography at the University of Bristol, commented: “The results significantly augment our understanding. Traditional climate models have found it challenging to portray the extent of the Sahara’s ‘greening.’ Our enhanced model not only captures historical changes accurately but also boosts our confidence in its ability to predict future shifts.”

The research, which involves climatologists from the University of Birmingham, is a component of a project funded by the Kone Foundation at the University of Helsinki that investigates the impact of climatic conditions on historical human distributions and their ecological niches.

Co-author Miikka Tallavaara, Assistant Professor of Hominin Environments at the University of Helsinki, noted: “The Sahara serves as a sort of gateway controlling the migration of species within North Africa and Sub-Saharan Africa, as well as into and out of the continent. This gateway was accessible when the Sahara was lush and impassable when it was desertified. This alternation between wet and dry periods had substantial repercussions for the migration and evolution of species in Africa. Our capability to accurately model these North African Humid Periods significantly advances our understanding of human migration patterns and the evolutionary trajectory of our genus within Africa.”

Reference: “North African humid periods over the past 800,000 years” by Edward Armstrong, Miikka Tallavaara, Peter O. Hopcroft, and Paul J. Valdes, published on 8 September 2023 in Nature Communications.
DOI: 10.1038/s41467-023-41219-4

Frequently Asked Questions (FAQs) about Sahara Desert’s Historical Greening

More about Sahara Desert’s Historical Greening

• Nature Communications Journal
• University of Helsinki Climate Research
• Earth’s Orbital Precession
• African Monsoon Dynamics
• Ice Ages and Climate Change
• Human Migration Out of Africa
• Kone Foundation
• University of Bristol Geography Department
• Paleoclimate Records
• DOI: 10.1038/s41467-023-41219-4