Research project NG| Simulating the Green Sahara with an Earth System Model
Marine sediments indicate that the Sahara region was about 10 times as wet as today.
Marine sediments indicate that the Sahara region was about 10 times as wet as today, dotted with large and small lakes and the vegetated area extended as far north as 31°N, creating a "Green Sahara".
Project description
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Earth System Model (1110 Kb)
As described in the novel The English Patient, what is now the world’s largest Sahara Desert was home to hunter-gatherers who made their living off the animals and plants that lived in region's savannahs and wooded grasslands some 5,000 to 11,000 years ago.
Climate changes in a Green Sahara period simulated by EC-Earth3. This figure shows the greening of Sahara will result in warming in Arctic. Greening of Sahara decreases the surface albedo, absorb more solar radiation, and lead to local warming. This creates a positive NAO, more heat is transported to Arctic region, and lead to Arctic warming.
Author: Qiong Zhang
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Green Sahara Climate (520 Kb)
Marine sediments indicate that Sahara region was about 10 times as wet as today, dotted with large and small lakes and the vegetated area extended as north as 31°N, thus created a “Green Sahara”.
The formation of Green Sahara was a direct result of African monsoonal climate responses to periodic variations in the Earth's orbit around the Sun.
During the green Sahara period the dust emissions were 70 to 80% lower than today. More interestingly, paleo dust record also shows that the beginning and termination of the Green Sahara period were abrupt, occurring within decades to centuries.
Early in 1990, Petit-Marie,
Earth System Model (1110 Kb)
, hypothesized that increase in atmospheric CO2 concentration would lead to a warmer climate that in some respect could resemble the Holocene climate optimum with its greener Sahara.
What happens now after almost 30 years? There are observational evidences that show that under current global warming the Sahel region has experienced a recovery in rainfall since 1980, after a 30-year persistent drought, and the region is becoming greener due to development of farming and effects of CO2 fertilization. Today’s satellite data does show CO2 fertilization effects lead to greening trends in the tropics and Sahel is among the largest greening region. Although these ongoing changes in climate and ecosystem have much smaller amplitude compared with the dramatic regime shift during mid-Holocene, these changes might be amplified to some extent due to the feedbacks in climate and ecosystem. Therefore, the ability of the ESM to represent the interaction within ecosystem and climate will provide credibility to the ESM in future projections.
Looking forward to the next few decades, greenhouse gas concentrations will continue to rise. This rise is favorable for sustaining, and potentially amplifying, the recovery of Sahel rainfall and greening of Sahel. The positive feedback between rainfall and vegetation will further amplify the monsoon and possibly lead to a northward shift of monsoon and extension of greening to Sahara.
In this project we use an ocean-atmosphere-vegetation coupled ESM to investigate how the local and remote climate response to the greening of Sahara. We assess the different role played by vegetation and dust in climate change by adding them one by one in the model. We simulate a 8000 years’ evolution of mid-Holocene climate driven by slowly changed insolation in the ESM and Green House Gas. These simulations on one hand enhance our understanding on the dramatic change in ecosystem, and provide a very useful test for the climate model during a transient climate like future climate projections.
Project members
Project managers
Qiong Zhang
Professor
Members
Ellen Berntell
Postdoctor
Qiong Zhang
Professor
More about this project
Publications
Green Sahara Publications (56 Kb)