Abstract
Abstract. Almost 90% of freshwater resources consumed globally are used to produce plant and animal commodities. Water-scarce countries can balance their water needs by importing food from other countries. This process, known as virtual water transfer, represents the externalization of water use. The volume and geographic reach of virtual water transfers is increasing, but little is known about how these transfers redistribute the environmental costs of agricultural production. The grey water footprint quantifies the environmental costs of virtual water transfers. The grey water footprint is calculated as the amount of water necessary to reduce nitrogen concentrations from fertilizers and pesticides released into streams and aquifers to allowed standards. We reconstructed the global network of virtual grey water transfers for the period 1986–2010 based on international trade data and grey water footprints for 309 commodities. We tracked changes in the structure of the grey water transfer network with network and inequality statistics. Pollution is increasing and is becoming more strongly concentrated in only a handful of countries. The global external grey water footprint, the pollution created by countries outside of their borders, increased 136% during the period. The extent of externalization of pollution is highly unequal between countries, and most of this inequality is due to differences in social development status. Our results demonstrate a growing globalization of pollution due to virtual water transfers.
Highlights
About 90 % of freshwater used by humans is allocated to agricultural production (Rost et al, 2008; Baron et al, 2002; Hoekstra and Chapagain, 2008)
The total grey water footprint of a country (GWFT) was calculated as the sum of the grey water production (GWP) and the net trade of grey water (GWNT), which is equal to the import–export balance between grey water imports (GWI) and grey water exports (GWE)
The externalization of pollution due to agricultural production is pervasive globally, and grey water network strength increased considerably during the study period (1986–2010; Fig. 4). This is a general result of the intensification of international trade and is consistent with previous reports of blue and green virtual water transfers during the same period (e.g., Carr et al, 2012a)
Summary
About 90 % of freshwater used by humans is allocated to agricultural production (Rost et al, 2008; Baron et al, 2002; Hoekstra and Chapagain, 2008). With the populations of some countries already exceeding their carrying capacity (defined by water resources), isolation from the international community may induce water and subsequent food crises (Seekell, 2011; Suweis et al, 2013) These countries can balance their water needs by importing plant and animal commodities from other regions. A consequence of this is consumers might not be directly affected by the environmental degradation resulting from the non-local production of (food) commodities (e.g., soil erosion and pollution from fertilizers and pesticides) In this manner, highly developed countries may be able to externalize pollution disproportionally relative to less developed countries. Our results indicate that the externalization of pollution is increasing and the burden of pollution is being concentrated in a handful of countries
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