Would planting the African “Great Green Wall” change the global climate?
Fifteen years ago the African Union announced an overly ambitious project, plant the Pan-African Great Green Wall (PAGGW). It is a natural barrier formed by a huge fringe of lined trees. The goal is to plant for the year 2030 ones 100 million hectares (8000 km long by 15 km wide), located along the Sahel, the semi-arid zone that covers the southern edge of the desert of Sahara. The purpose of this wall of trees is prevent the Sahara desert from expanding south.
Once completed, the “Great Green Wall” it will be the largest living structure on the planet, it will have three times the size of the Great Barrier Reef.
Recently, the president of Nigeria, Muhammadu Buhari, assumed the leadership of PAGGW, as they reaffirmed during the COP26 Conference, in Glasgow, last December 2021. Basically, the project points out that during the next two years that country will work assiduously to address the problems of land degradation, desertification, food security, climate change, the depletion of forest ecosystems and biodiversity in Africa.
Trying to stop climate change
The region called Sahel, in Africa, is bordered to the north by the Sahara desert and to the south by the Sudanese steppe. Barely 15 years ago this site was covered with forest and inhabited by a valuable biodiversity, unfortunately the ecosystem changed drastically. This area was fertile, but today the 65% of its land is degraded.
The extremes like strong rains but also prolonged droughts, They led to devastating landslides and wildfires, turning the Sahel into a tangible stage of the climate crisis, an absolutely deteriorated landscape. The massive loss of fertile land in the last 30 years is of great concern, because the 80% of the population still depends on rainfed agriculture, there the people depend on their productivity on the land to be able to survive.
Objectives of the “Great Green Wall”
The PAGGW project has the financial support of the World Bank, the EU, the United Nations and others, in order to restore degraded lands and help the people of the Sahel to produce food, create jobs, prevent people from migrating or move and promote peace. A project of great scope and of important dimensions is proposed: restablish more than 100 million hectares for productive agriculture.
Until now only 15% of the objective set in 2007 has been achieved with a proposed completion date of 2030. The reasons for this slow pace in the construction of the Great Green Wall are mainly due to the lack of funds.
“Green Sahara” and its possible severe consequences on the climate
According to a recently published study, whose main author is Francesco SR Pausata, from the University of Quebec, in Montreal, shows how new climate simulations of the past and future of the Sahara They suggest that this green PAGGW initiative could change the climate in North Africa, and even in the Mediterranean.
In the Sahara and Sahel region, rainfall is closely related to intensity of the West African Monsoon (WAM), which is crucial to the socioeconomic stability of millions of people living in sub-Saharan Africa.
One of the most dramatic changes in WAM occurred between 12 and 5 thousand years ago, when the increased summer rainfall led to an expansion of North African lakes and wetlands, and an extension of grasslands and scrub in areas that are now deserts, giving rise to the so-called “Green Sahara” or the African Wetlands.
That period in the past offers a great opportunity to learn, obtain information and critically assess the global ramifications associated with potential natural or geoengineered greening from the Sahel and Sahara region, scientists explain.
They analyzed how the feedbacks of the land cover and associated changes in dust emissions, for example, play a critical role in the strength of the monsoon. In addition, they studied what global impacts the WAM intensification could have on ENSO variability, for example.
According to the results they presented at the December 2021 meeting of the American Geophysical Union, The plan of this wall of trees could significantly increase rainfall within the Sahel, even doubling it. Previous studies have shown that an increase in the amount of vegetation is a local source of moisture, with an increase in the cycles of water from the soil to the atmosphere, thus increasing the amounts of precipitation.
Regarding temperatures, this research suggests that PAGGW would lead to lower average summer temperatures in much of North Africa and in the Mediterranean, would reduce average summer temperatures by up to 1.5 °C in most of the Sahel. But on the other hand, temperatures in the hottest parts of the desert would become even higher.
And this is because plants also create a darker earth’s surface, therefore the ground would absorb more heat, and added to that vegetation reduces the amount of dust in suspension in the atmosphere, resulting in more solar radiation reaching the earth.
Previous studies have shown that a “Green Sahara” is associated with changes in the intensity and location of the West African monsoon. If higher temperature values are recorded, added to the increase in the humidity contribution, it will result in a greater difference in atmospheric pressure and consequently the monsoon winds would be much more intense.
Therefore, in view of these preliminary results, the authors of this research work suggest that before carrying out this enormous and unprecedented tree-planting work, an in-depth study is made of what the final effects on the local and global climate would be if it were to materialize. Knowing the impact that this green project will leave is of vital importance.