F ig. 1. The components of the EF differences in focus between Wackernagel and R ees and this paper are indicated close pattern.
3. Methodology
In the previous section, we discussed the EF concept and decided to introduce a few changes in
the calculation procedures. The resulting method- ology is nevertheless based on Wackernagel and
R ees 1996, Wackernagel et al. 1997; the most fundamental differences are indicated in Table 1.
In our calculations two main categories of re- source use are: 1 the EF for land — subdivided
into arable landpastures, forest and built-up area — and 2 the ecological footprint for carbon
dioxide emissions see F ig. 1. We have estimated these EF s for Benin, Bhutan, Costa R ica and the
N etherlands for 1980, 1987 and 1994.
3
.
1
. L and use The data used in this study have been mainly
taken from the statistics of the U nited N ations’ F ood
and Agricultural
Organisation F AO,
1995 – 1998, assuming that this would make the results more comparable between countries. We
have compared these data, if available, with data from national sources mainly from statistical
offices of the countries involved, Chhewang R inzin, 1997; Orozco and Acun˜a, 1997. In most
cases the different sources did match well; if not, we have used those considered to be most reliable
on the basis of available information as described in detail in van Vuuren et al., 1999a. F or animal
and wood products in the N etherlands more data was needed than available from F AO and na-
tional data have been used in particular CBS, 1994 – 1996.
A simplified equation for our calculations is indicated see Eq. 1. F or some product cate-
gories calculation schemes were more complex, as these products are further processed for instance,
wheat into bread. In that case, also imports and exports of manufactured products have to be
taken into account.
land –use=
c
prod
dom, c
yield
dom, c
+ import
c
yield
imp, c
− export
c
yield
exp, c
1
In Eq. 1 land –use is the net EF for land use in hectares. Suffix c indicates the different produc-
tion categories. The variables prod, import and export are domestic production and imports and
exports, respectively, in tons per year. The vari- ables yield
dom
, yield
exp
and yield
imp
are equal to the domestic yield or the yields that can be at-
tributed to imports and exports, all in tons per ha per year. In our calculations, yields for exports
have been set equal to domestic yields except for re-exports and the yields for imports to the yields
of the region from which products are imported; if unknown, global average yields were used for
these imports.
D ata on yields are included in the F AO statis- tics for most agricultural products. F or wood
products, however, reliable data on productivity were more difficult to find. We have used the
estimates made by Stolp and Eppenga 1998 on productivity of natural forests in different parts of
the world. The data used for built-up land refer only to domestic land use; time trends were only
available for the N etherlands. F or the other three countries, domestic land use has been assumed to
grow along with the size of the population. The exact calculations, assumptions and data sources
are described in van Vuuren et al. 1999a.
3
.
2
. EF for carbon diox ide emissions F or the 1985 – 1994 period for the N etherlands,
earlier calculations
by R IVM
and Statistics
N etherlands R IVM , 1998; CBS, 1998 could be used in which the EF for carbon dioxide emis-
sions was assessed on the basis of: 1 consump- tion statistics, 2 energy intensities per product
and 3 types of energy consumed. F or 1980, we have estimated net carbon dioxide emissions on
the basis of normal carbon dioxide emissions statistics and trends in the 1985 – 1997 period.
D omestic carbon dioxide emissions in Benin, Bhutan and Costa R ica have been calculated us-
ing energy consumption statistics as collected by van Vuuren and de K ruijf 1998. F or carbon
dioxide emissions related to net imports of manu- factured goods in Costa R ica, we have used the
results of Wackernagel et al. 1997. F or Bhutan and Benin, we concluded on the basis of available
trade statistics that the carbon dioxide emissions attributed to the net import of products will be
relatively small. H owever, we considered available statistics and energy intensities which have been
determined for industrialised countries only to be insufficiently reliable to calculate the size of these
emissions
— and
thus only used domestic
emissions.
4. Results
