Conneting Humans, Vegetation and Desertification:
Charney's Hypothesis
In 1975, Charney et al published an influential paper outlining a biogephysical feedback mechanism that attempted to help explain the global advancement of deserts. This classic paper, not without its criticism, speculated that an increase in albedo as a result of a decrease in plant cover (overgrazing, misuse of the environment etc.) causes a decrease in rainfall because of the reduced temperature and hence convective potential in the atmosphere. Subsidence in the troposphere would initiate the feedback processes of reduced precipitaiton and reduced plant growth and hence develop a potentialy devestating and never-ending cycle ending in continued desertification. This cycle raises interesting questions. Reduced vegetation can be a result of drought, but also as a direct consequence of human intervention and misuse of resources. The biogeophysical feedbacks (anthropogenically or naturally induced) leads to a host of other ‘societal’ feedbacks. Desertification leads to a decrease in the productivity of land, social marginalisation, population pressures, further overgrazing etc etc. So whatever your take on the causes of the biogeophysical cycle one thing is for sure, the consequences can be vast. The interaction of these processes is neatly depicted below. We have to ask what can be done about the externalities associated with desertification as we move deeper into the anthropocene, and humans have an ever increasing power over the environment.
Desertification, Global Climate Change and Biodiversity Loss
As this figure indicates, climate change, desertification and biodiversity loss are linked between each others. Theses feedbacks are two-way and positive. Scientists says that global warming accelerates desertification, but desertification also promotes global warming by increasing CO2 concentration. Likewise biodiversity loss and desertification affect each other. If you consider the feedbacks of 'climate-desertification' and 'biodiversity loss-desertification', you can see these two feedbacks affect desertification by only one factor, soil erosion. It means that soil erosion is the keyword of desertification, and it is mainly impacted by biodiversity losses. Overall feedback is also positive, so desertification can be accelerated today.
