Climate change has achieved what Bob Geldof and Live Aid failed to do by ending the drought in the Sahel region of Africa that killed more than 100,000 people in the 1980s, a study has found.
Rising greenhouse gases caused rains to return to the region south of the Sahara, from Senegal to Sudan, boosting crop yields since the 1990s and helping the population to feed itself without relying on foreign donations.
The rare positive effect of climate change is identified in a study which concludes that the continued rise in emissions is “favourable for sustaining, and potentially amplifying, the recovery of Sahel rainfall”.
A weather chart showing how average rainfall in the Sahel was very low in the 1980s but is now increasing again
The natural variability of Sahel rainfall
Rowan Sutton, a professor at the national centre for atmospheric science at the University of Reading and co- author of the study, said: “Amounts of rainfall have recovered substantially. It was a surprise that the increase in greenhouse gases appears to have been the dominant factor.”
The study, in the journal Nature Climate Change, found that Sahel summer rainfall was about 10 per cent, or 0.3mm, higher per day in 1996-2011 than in the drought period of 1964-93.
Professor Sutton said: “This might not sound like a big number but in fact it’s a substantial shift in the context of this region and the very severe drought experienced in the 1970s and 1980s.”
The scientists, using a supercomputer climate simulator, said that heat-trapping emissions accounted for three quarters of the recovery in rainfall, rather than other suggested factors such as changes in sea temperature.
Warming by greenhouse gases means that air can hold more moisture, bringing more rains, and can shift winds, influencing the monsoon.
Professor Sutton cautioned that the change in rainfall was only local and that many parts of Africa faced problems from global warming, including heatwaves, desertification, floods, rising sea levels and an increase in malaria. “It would be naive to conclude that this is a good thing for Africa,” he said. “In future, there are other effects — the rise in temperatures can be detrimental to crops.”
He said that other impacts of climate change, such as changes in the temperatures of the Atlantic and Indian oceans, could cause drought to return to the Sahel.
The Stockholm Resilience Centre said the greening of the Sahel was also the result of changes in farming practice. “Farmers have actively managed their land in ways that have enhanced its productivity,” the centre said.
Mike Hulme, professor of climate and culture at King’s College London, said the study was relevant to the debate about whether rich countries should compensate poor ones for the damage done by emissions.
He said: “One should continue to remain sceptical of overconfident claims that ‘climate change’, by which is meant fossil fuel emissions, always causes negative effects in these African drylands.”
Philipp Mueller: The Sahel Is Greening
Global warming has both positive and negative impacts. However, very often only the negative consequences are reported and the positive ones omitted. This paper 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 1980.6 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.
Causes of the greening
The main reason for the greening of the Sahara and the Sahel has been an increase in rainfall since the mid-1980s.
Of the 40 rainfall stations across the Sahel, most of them have been observing an increase in rainfall.If sustained, the increasing rainfalls could revitalize drought-ravaged regions, reclaiming them for farming.
The United Nations’ Africa Report of 2008 confirmed that the greening of the Sahel is now well established and that increases in rainfall are the main driver of the change in the vegetation cover. The report noted that there was a 50% increase in vegetation in parts of Mali, Mauritania and Chad during 1982-2003.
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-wind erosion 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.