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Famine follows the plough in Africa: A ‘dusty’ connection

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A famine provoked by drought, spread over five decades, threatens millions in the sub- Saharan Sahel region of Africa with crop failure, cattle loss, starvation and death. As policy makers scratch their heads to come up with plans to mitigate food and water security for the drought ravaged nations, scientists in Europe have found an answer to the cause that may have snowballed a minor ‘dry spell’ into a drought so severe, that it now threatens political stability in sub-Saharan Africa.
It turns out that aggressive commercial farming practices, introduced in the Sahel by Portuguese settlers between 18th and the 19th century, may have been the culprit. New research, published last year in Nature, shows that dust emission from West African Sahel increased almost exponential from the early part of the 18th century. Mud samples collected from the bottom of Atlantic Ocean, bordering the coast of Mauritania in Western Africa, shows distinctive grain size and chemical signatures that can be attributed to variations in emission of dust from North Africa and subsequent deposition over the last three thousand years. In addition to dry environments that are characteristic climatic features of the Sahel old farming practices, still prevalent, loosens parched top soil causing large volumes of it to be lofted into the atmosphere by wind. Once in the atmosphere dust from North Africa can travel long distances across the Atlantic Ocean, in matter of weeks.
 
Dust during its transit can lead to localized heating in the atmosphere by interacting with incoming solar radiation. Such differential heating impedes atmospheric mixing that is necessary for rainfall. Additionally, dust in atmosphere changes cloud properties preventing them from raining out. Both of these effects lead to a net reduction in rainfall, even in areas far removed from the dust sources. African dust also impacts air quality in Western Europe and United states. It is now being suggested that North African dust can potentially reduce hurricane frequency over the Atlantic. Atlantic hurricanes are responsible for billions of dollars every year in life and property damage in the US
 
Dr. Stefan Mulitza and coworkers, the principal investigators of this study, have shown that for three thousand years, dust emission from West Africa was regulated by frequently occurring droughts in the region. Detailed statistical techniques employed by Dr. Mulitza and his group, show that droughts in the Sahel leads to reduction in moisture that increases dust emission. Such ‘dry spells’ in the Sahel is mainly regulated by variations in sea-surface temperature in the Atlantic Ocean, as suggested by a study published in Science by Dr. Timothy Shanahan at the University of Texas at Austin in 2009.
From the mid 18th century however, the increase in dust emission from North Africa, as recorded in mud samples from the coast of Mauritania, is far greater than can be explained by reduction in rainfall. Dr. Mulitza argues that increasingly vanishing control of droughts on North African dust emission from the mid 18th century till the present is due to aggressive commercial farming practices introduced in the Sahel around the same time.
Such farming practices kick off phenomenal quantities of dust in the atmosphere that was so far, grossly underestimated. This study for the first time lends observational evidence what scientists had long suspected: dust emitted from human activities like farming in the Sahel may have added to the dust budget from North Africa in ways that can lead to increasing severity and duration of naturally occurring droughts. Some scientists have questioned the statistical methods employed by the authors when considering the relationship between drought and dust emission. They have also argued that the reported increase in the dust is more reflective of local conditions and not the Sahel in general.
 
However, there is no denying the fact that this study provides observational data that climate modelers can use to come up with realistic predictions about the future of the ongoing drought in the Sahel. But more importantly, this study has grave implications for commercial farming practices, especially in dry regions. And not just in Africa. In the southwest United States, in the late 1930’s malpractices in farming techniques led to the dust bowl and consequently the biggest economic downturn in American history. The southwest US is currently going through another drought period and these new findings should serve as a caution that dust emissions should be taken into serious consideration when planning commercial agriculture, to avoid potential environmental disasters.

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