Climate Change and Agriculture - The Oxford Topic of Food, Politics, and Society - page 456

to suffer, whereas farmers and developers who gain access to the newly cleared land
benefit.
Soil degradation reduces potential production. Removing more nutrients from the
soil than are returned through fertilization is called soil mining. High levels of soil min-
ing can lead to desertification and can be very expensive to reverse. In sub-Saharan
Africa, 85 percent of agricultural land loses at least 30 kg/ha in nutrients annually,
and half of that land loses more than 60, varying from 9 kg/ha in Egypt to 179 kg/ha in
Uganda (Henao and Baanante 2001; Nkonya et al. 2008). In addition to the problems of
soil mining, overuse or poor fertilizer-application technique can result in burnt soils and
water pollution. Because of the high organic matter content of top soils, even low levels
of soil erosion lead to large yield losses. Poor irrigation practices lead to waterlogging or
salinization. These problems plus overgrazing and deforestation have caused more than
two-thirds of global soil degradation since 1945 (de Haen 1997). Pinstrup-Andersen
(2002) argues that soil degradation is caused or worsened by a variety of factors, many
of which are beyond farmers' control: poor property rights and land tenure issues;
population pressure; government policies; poor market access; and technologies and
techniques that are not sustainable. Fifteen percent of manmade greenhouse gas emis-
sions come from agriculture, with methane from livestock a leading contributor (Popp,
Lotze-Campen, and Bodirsky, 2010).
The Green Revolution provided a mixed bag of positive and negative externalities
for environmental quality (Harriss and Stewart, this volume). On the negative side was
the greater reliance on monoculture cropping (which decreased farmer interest in pre-
serving biodiversity on their lands) poor water management, and improper pesticide
and fertilizer-application practices. These were not necessary features of the Green
Revolution per se, but certainly accompanied the increased reliance on irrigation, fertil-
izer, and pesticides. Most of these negative effects could have been prevented by incor-
porating social costs into private prices. On the positive side, however, the increased
productivity made possible by improved seed varieties and agricultural intensification
reduced demands on human expansion onto marginal lands. Goklany (1998) estimates
it would have required 80 percent more land to provide the increased food produced
between 1961 and 1993 without the spread of Green Revolution technologies. Preserving
the marginal lands that would have otherwise been cleared and plowed simultaneously
preserved biodiversity, reduced soil erosion and deforestation, and preserved environ-
mental services to the nearby communities. Costanza, et al. (1997) estimate that global
environmental services are worth between $16 and $54 trillion, which, at the time of the
study, was one to three times the value of all human production.
Improving agricultural productivity is essential for both preservation of environ-
mental services and for poverty reduction. Schlenker and Lobell (2010, p. 7) agree with
World Bank (2007): “There is arguably little scope for substantial poverty reductions
in SSA [sub-Saharan Africa] without large improvements in agricultural productivity.”
Making land, water, and labor more productive is essential for poverty reduction and
feeding a growing global population while preserving marginal lands and biodiversity.
Current practices fall well short of those that would simultaneously ensure sufficient