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Soil erosion, climate change and global food security: challenges and strategies

Posted on 23. June, 2014.

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There are particular instances in history, where publication of a book has endowed a critical shift in human thinking as its legacy. Man and Nature; Or Physical Geography as Modified by Human Action is one such example, written by George Perkins Marsh. 

Published in 1864, this is probably the first time that the effects of human actions on the environment were documented, hence auguring-in what we now think of as the conservation movement. It was Marsh’s thesis that ancient Mediterranean civilisations collapsed as a result of land degradation: deforestation caused soils to become eroded, so declining in their productivity.

In this article, an overview is presented of the determined degree of global land degradation (principally occurring through soil erosion), with some consideration of its possible impact on global food security. Most determinations of the extent of land degradation (e.g. GLASOD) have been made on the basis of “expert judgement” and perceptions, as opposed to direct measurements of this multifactorial phenomenon. 

More recently, remote sensing measurements have been made which indicate that while some regions of the Earth are “browning” others are “greening”. The latter effect is thought to be due to fertilisation of the growth of biomass by increasing levels of atmospheric CO2, and indeed the total amount of global biomass was observed to increase by 3.8% during the years 1981 – 2003. 

Nonetheless, 24% of the Earth’s surface had occasioned some degree of degradation in the same time period. It appears that while long-term trends in NDVI (normalised difference vegetation index) derivatives are only broad indicators of land degradation, taken as a proxy, the NDVI/NPP (net primary productivity) trend is able to yield a benchmark that is globally consistent and to illuminate regions in which biologically significant changes are occurring. Thus, attention may be directed to where investigation and action at the ground level is required, i.e. to potential “hot spots” of land degradation and/or erosion.

The severity of land degradation through soil erosion, and an according catastrophic threat to the survival of humanity may in part have been overstated, although the rising human population will impose inexorable demands for what the soil can provide. However, the present system of industrialised agriculture would not be possible without plentiful provisions of cheap crude oil and natural gas to supply fuels, pesticides, herbicides and fertilisers. It is only on the basis of these inputs that it has been possible for the human population to rise above 7 billion. Hence, if the cheap oil and gas supply fails, global agriculture fails too, with obvious consequences.

Read the full article in Science Progress, Volume 97, Number 2, June 2014, pp. 97-153

Keywords: soil organic matter, global warming, climate change, global food security, land degradation, soil degradation, soil erosion, population

Author: Christopher J.Rhodes


Image: The soil food web. Adapted from USDA.