Energy and Human Ambitions on a Finite Planet, 2021a

2 Economic Growth Limits 19
Definition 2.1.1 <strong>Energy</strong> intensity is a measure of how much energy a
society uses relative to its economic scale—sort of like an efficiency. It can be
a proxy for resource use in general, <strong>and</strong> is calculated as:
<strong>Energy</strong> Intensity
<strong>Energy</strong> Expended
. (2.1)
Money Spent
In a resource-constrained world (limited material <strong>and</strong> energy supplies), a
lower energy intensity translates to less energy consumption for a certain
economic output, or conversely allows higher economic output for a fixed
energy consumption rate. On a smaller scale, we can say, for instance, that
spending $100 on an airplane trip is far more energy intense than spending
the same amount of money on legal advice.
<strong>Energy</strong> intensity therefore provides a measure of how resource-heavy a
country is in relation to the size of its economy. For instance, the U.S. uses
about 10 20 Joules of energy per year <strong>and</strong> has a GDP of approximately We will cover units of energy in Chapter 5.
20 trillion dollars. Dividing these gives an intensity of 5 × 10 6 J/$, or For now, it is sufficient to know that a Joule
(J) is a unit of energy, <strong>and</strong> that MJ means
5 MJ/$ (many variants are possible in terms of units). The world as
megajoules, or 10 6 J.
a whole uses about 4.5 × 10 20 J in a year at an estimated $90 trillion
gross world product, also resulting in 5 MJ/$. The variation among
developed countries is not especially large—generally in the single-digit
MJ/$ range.
Venezuela
Russia
<strong>Energy</strong> Intensity (MJ/$)
10
1
Pakistan
India
Nigeria
Brazil
Indonesia
China
Canada
USA
Spain
Japan
Germany
Italy
Luxembourg
UK
Taiwan
Switzerl<strong>and</strong>
1000 10000 100000
Per Capita GDP ($)
Figure 2.2: <strong>Energy</strong> intensity of countries,
on a log–log plot. The vertical axis shows
how energetically “hungry” each country is
in relation to its economic output, while the
horizontal axis sorts countries by economic
output per person. A few instructive cases
(red dots) are labeled. The dot areas are
scaled to population. Prosperous countries
tend to have lower intensity than developing
countries, but part of this may relate to
moving manufacturing from the former to
the latter [6–8].
Figure 2.2 illustrates the range of intensities for all the countries in the
world. Among the factors driving energy use are geographical extent
(large countries require more long-haul transportation), climate (cold
countries require more heating), efficiency, <strong>and</strong> lifestyle. Russia, Canada,
<strong>and</strong> the U.S. have large territories, <strong>and</strong> the former two require more
heating than most. By contrast, Taiwan is geographically small <strong>and</strong>
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.