Energy and Human Ambitions on a Finite Planet, 2021a

2 Economic Growth Limits 21
the face of non-replicable circumstances. Not every country can assume
the geography <strong>and</strong> financially-focused nature of Switzerl<strong>and</strong>. And at
the same time, if the U.S. imagines itself providing a model that other
countries might emulate, the intensity of many European countries could
actually increase if adopting U.S. habits. But more broadly, we don’t
have evidence that a country on the prosperous end of the distribution
can operate at even a factor-of-four lower intensity than the 4 MJ/$ level
typical of developed countries. In the present context of assessing the
future of growth, in which we are concerned with order-of-magnitude
scales <strong>and</strong> limits (as in Chapter 1), it does not appear that decoupling
has very much to offer. 10
Definition 2.2.2 Substitution refers to the ability to switch resources when
one becomes scarce or a better/superior alternative is found. Substitution is
often invoked to counter concerns about scarcity. A common <strong>and</strong> cute way to
frame it is that the stone age did not end because we ran out of stones—we
found bronze.
The past is full of examples of substitution (Definition 2.2.2). Consider the
progression in lighting technology from open fires to beeswax c<strong>and</strong>les
to whale oil lanterns to piped gas lanterns to inc<strong>and</strong>escent electric bulbs
to fluorescent lights to LED (light emitting diode) technology. Every step
seems to be an improvement, <strong>and</strong> it is very natural to assume the story
will continue developing along these lines.
10: That is, no orders-of-magnitude that
will allow us to continue growth for centuries
more after physical resources limit
growth.
Through this example, we can see how
substitution <strong>and</strong> decoupling might be connected:
efficiency improves through substitution,
requiring less energy for the same
lighting value.
Box 2.1: A Story of Lighting Efficiency
One way to quantify lighting progress is in the luminous efficacy of
light, in units of lumens per Watt. In the 20th century, inc<strong>and</strong>escent
bulbs were so ubiquitous for so long that we fell into the bad habit of
characterizing brightness in terms of the electrical power consumed
by the bulb, in Watts. Thus we have generations of people accustomed
to how bright a “100 W” or “60 W” bulb is. As technology changes, we
should migrate to “lumens,” which accurately captures how bright a
source is perceived by the human eye.
Bulb packaging still refers to the “equivalent
wattage” of a bulb, even though a “60 W
equivalent” bulb may only consume 12 W
of power.
Table 2.1 <strong>and</strong> Figure 2.3 present the evolution of luminous efficacy as
sources improved. Can this trend continue indefinitely? No. Every
photon of light carries a minimum energy 11 requirement based on its
11: We will see this in Sec. 5.10 (p. 79).
wavelength. For photons spread across the visible spectrum (creating Table 2.1: Luminous efficacies [10, 11].
light we perceive as white), the theoretical limit is about 300 lm/W
[9]. At this extreme, no energy is wasted in the production of light,
Light Source lm/W
putting 100% of the energy into the light itself. Engineering rarely
C<strong>and</strong>les ∼0.3
reaches theoretical limits, due to a host of practical challenges. It
Gas Lamp 1–2
would therefore not be surprising if lighting efficiency does not
Inc<strong>and</strong>escent 8–15
Halogen 15–25
improve over where it is today by another factor of two, ending yet
CFL 45–75
another centuries-long trend.
LED 75–120
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.