Dieter Helm and his colleagues estimated the footprint of each pound’s
worth of imports from country X using the average carbon intensity of
country X’s economy (that is, the ratio of their carbon emissions to their
gross domestic product). They concluded that the embodied carbon in im-
ports to Britain (which should arguably be added to Britain’s official car-
bon footprint of 11 tons CO2e per year per person) is roughly 16 tons CO2e
per year per person. A subsequent, more detailed study commissioned by
DEFRA estimated that the embodied carbon in imports is smaller, but still
very significant: about 6.2 tons CO2e per year per person. In energy terms,
6 tons CO2e per year is something like 60 kWh/d.
Here, let’s see if we can reproduce these conclusions in a different way,
using the weights of the imports.
Figure H.2 shows Britain’s imports in the year 2006 in three ways: on
the left, the total value of the imports is broken down by the country of
origin. In the middle, the same total financial value is broken down by the
type of stuff imported, using the categories of HM Revenue and Customs.
On the right, all maritime imports to Britain are shown by weight and bro-
ken down by the categories used by the Department for Transport, which
doesn’t care whether something is leather or tobacco – it keeps track of
how heavy stuff is, whether it is dry or liquid, and whether the stuff arrived
in a container or a lorry.
The energy cost of the imported fuels (top right) is included in the
standard accounts of British energy consumption; the energy costs of all
the other imports are not. For most materials, the embodied energy per
unit weight is greater than or equal to 10 kWh per kg – the same as the
energy per unit weight of fossil fuels. This is true of all metals and alloys,
all polymers and composites, most paper products, and many ceramics,
for example. The exceptions are raw materials like ores; porous ceramics
such as concrete, brick, and porcelain, whose energy cost is 10 times lower;
wood and some rubbers; and glasses, whose energy cost is a whisker lower
than 10 kWh per kg. [ ]
We can thus roughly estimate the energy footprint of our imports sim-
ply from the weight of their manufactured materials, if we exclude things
like ores and wood. Given the crudity of the data with which we are work-
ing, we will surely slip up and inadvertently include some things made of
wood and glass, but hopefully such slips will be balanced by our underes-
timation of the energy content of most of the metals and plastics and more
complex goods, many of which have an embodied energy of not 10 but
30 kWh per kg, or even more.
For this calculation I’ll take from the right-hand column in figure H.2