14-06-2013, 12:14 PM
Carbon and Water Footprints
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Introduction
The Earth’s climate is changing as a result of anthropogenic
activity since the start of the industrial revolution. There
is growing scientific evidence that burning fossil fuels
contributes to rising temperatures and extreme weather
events (Mitchell et al., 2006; Rosenzweig et al., 2001;
Solomon et al., 2007). The public and decision-makers
have started to recognize the need for action to mitigate
global warming (Goodall, 2007). Governments, policymakers
and businesses have been urged to seek ways
to reduce greenhouse gas (GHG) emissions in response
to growing interest and concern about climate change
over the past two decades (Bo et al., 2008; Brenton et
al., 2009; Courchene and Allan, 2008; Matthews et al.,
2008). This brings the need to understand what activities
drive GHG emissions and how they can be effectively
reduced. The ‘carbon footprint’ (CF) concept has become
a popular tool to estimate GHG emissions related to
human activities (Moss et al., 2008; Wiedmann, 2009;
Wiedmann and Minx, 2007).
Origins of the
carbon and water
footprint concepts
The carbon and water footprint concepts were introduced
about a decade ago, simultaneously, but independently
from one another. The CF arose out of the debate on
climate change, as a tool to measure GHG emissions.
The WF was introduced in the field of water resources
management, as a tool to measure water use in relation
to consumption patterns. In both cases, the terminology
chosen was inspired by the ecological footprint (EF),
which had been introduced in the 1990s (Rees, 1992).
All footprints measure, in different ways, human appropriation
of the planet’s natural resources and carrying
capacity (Galli et al., 2012; Giljum et al., 2011; Hoekstra,
2009) (Figure 1). The EF measures the use of bioproductive
space in hectares; the WF measures the consumption
and contamination of freshwater resources in cubic
metres per year; and the CF measures the emission of
gases that contribute to heating the planet in carbon
dioxide (CO2)-equivalents per unit of time or product. A
common property of all footprints is that they can be
related to specific activities, products and consumption
patterns. Recently, the nitrogen footprint was introduced
as a tool to measure the amount of nitrogen released into
the environment in relation to consumption (Leach et al.,
2012). In this report, we focus on the CF and WF.
The water footprint
The WF concept is primarily rooted in the desire to illustrate
the hidden links between human consumption and
water use and between global trade and water resources
management (Hoekstra and Chapagain, 2007, 2008).
The WF was developed as an analogy to the EF concept.
It was first introduced by Hoekstra in 2002 to provide
a consumption-based indicator of water use (Hoekstra,
2003). It is an indicator of freshwater use that shows
direct and indirect water use of a producer or consumer.
The first assessment of national WFs was carried out by
Hoekstra and Hung (2002). A more extended assessment
was done by Hoekstra and Chapagain (2007, 2008) and
a third, even more detailed, assessment was done by
Hoekstra and Mekonnen (2012a).
Spatial and temporal dimensions
When determining CFs, GHG emissions are usually
estimated with the help of emission factors. Emission
factors are available for a wide range of processes (WRI
and WBCSD, 2004). Most CF studies are based on global
average data on emissions per unit of good or service.
However, national emission factors have also been introduced
to reflect divergent local characteristics (Solomon
et al., 2007). WFs provide spatiotemporally explicit
information on how water is appropriated for various
human purposes. In WF accounting, the approach is to
use local productivities (Mekonnen and Hoekstra, 2011,
2012). Obviously, at the global level it does not matter
whether footprint analysis is carried out on the basis of
local or global average productivities, because adding
the results obtained with local data will yield the same
global result as an analysis based on global average data.
But on a national level, the result will differ when local
productivities are used instead of global averages.