Vergroening van de Sahel

Door alle kommer en kwel die de klimaatalarmisten, versterkt door de megafoon van de reguliere media, voortdurend over ons uitstorten, worden de positieve klimatologische ontwikkelingen in de wereld aan het oog onttrokken. Niet minder dan spectaculair is in dit verband de vergroening van de Sahel, die nu al tientallen jaren plaatsvindt.

In een brochure, van de GWPF (Global Warming Policy Foundation), getiteld: 'The Sahel is greening', schrijft Philipp Mueller daarover:

Global warming has both positive and negative impacts. However, very often only the negative consequences are reported and the positive ones omitted. This article will show an example of a positive effect of warming. The people living in the Sahel, a semiarid area just south of the Sahara desert, spanning the entire African continent from the Atlantic Ocean to the Red Sea, were suffering from several devastating droughts and famines between the late 1960s and the early 1990s. The draughts were triggered by decreases in rainfall from the early 1950s to the mid-1980s. Global warming was supposed to increase the frequency and severity of the droughts, which would make crop-growing unviable and cause even worse famines. According to the United Nations, the outlook for the people in the Sahel was bleak. However in sharp contrast to this gloomy outlook, it seems that global warming has exactly the opposite effect on the Sahara and the Sahel.

The Sahara is actually shrinking, with vegetation arising on land where there was nothing but sand and rocks before. The southern border of the Sahara has been retreating since the early 1980s, making farming viable again in what were some of the most arid parts of Africa. There has been a spectacular regeneration of vegetation in northern Burkina Faso, which was devastated by drought and advancing deserts 20 years ago. It is now growing so much greener that families who fled to wetter coastal regions are starting to come back.

There are now more trees, more grassland for livestock and a 70% increase in yields of local cereals such sorghum and millet in recent years. Vegetation has also increased significantly in the past 15 years in southern Mauritania, north-western Niger, central Chad, much of Sudan and parts of Eritrea. In Burkina Faso and Mali, production of millet rose by 55 percent and 35 percent, respectively, since 1980. Satellite photos, taken between 1982 and 2002, revealed the extensive re-greening throughout the Sahel. Aerial photographs and interviews with local people have confirmed the increase in vegetation.

The main reason for the greening of the Sahara and the Sahel has been an increase in rainfall since the mid-1980s. ... Vegetation changes play a significant role in the rainfall variability. The increase in rainfall has allowed more plants to grow, which in turn increases precipitation even more. Plants transfer moisture from the soil into the air by evaporation from their leaves and hold water in the soil close to the surface, where it can also evaporate. The darker surface of plants compared with sand also absorb more solar radiation, which can create convection and turbulence in the atmosphere which might create rainfall.

Vegetation effects account for around 30 percent of annual rainfall variation in the Sahel. The increased vegetation will fix the soil, enhance its anti-winderosion ability, reduce the possibility of released dust and consequently cause a decline in the numbers of sand-dust storms.

However, the greening cannot be explained solely by the increase in rainfall. There were vegetation increases in areas where rainfall was decreasing, suggesting another factor was responsible for the greening in these areas. This other factor might have been the rise of atmospheric CO2 levels. The aerial fertilization effect of the ongoing rise in the air’s CO2 concentration increases greatly the productivity of plants. The more CO2 there is in the air, the better plants grow. Rising atmospheric CO2 levels also have an antitranspiration effect, which enhances the water-use efficiency of plants and enables them to grow in areas that were once too dry for them.

De huidige situatie is overigens niets nieuws.

The greening of the Sahara and the Sahel is not unprecedented. During the Holocene Climate Optimum (9000-4000 BC), whose early and middle parts were possibly 2-5 degrees Celsius warmer than now, the northern half of Africa received more abundant and more stable rainfall. What is now the Sahara desert was a green savannah then. Rock paintings in south-eastern Algeria from this period show savannah animals such as elephants and zebus (cattle). Bones of crocodiles and hippos were found in the Sahara together with sediments showing that big lakes and rivers existed there until 6,000 years ago.

Lees verder hier.

Wie had ooit gedacht dat aan opwarming (die overigens al zo'n tien jaar geleden is gestopt) en CO2 een positieve invloed zou worden toegeschreven?

Volgens het 'grote klimaatverhaal' zou Afrika verdorren. In werkelijkheid is het andersom.

Alweer een klimaatsprookje minder.