6 March 2021 | New Scientist | 15THE world is failing to account
for a rebound effect that could
wipe out more than half of the
savings from energy efficiency
improvements like cleaner cars,
making the goals of the Paris
Agreement on climate change
even harder to hit.
Improvements to energy
efficiency, from LED lights
to better steel-making arc
furnaces, are seen by many
authorities as a top priority
for cutting carbon emissions.
Yet a growing body of research
suggests that human behaviour
and economics mean a major
chunk of anticipated efficiency
savings are lost.
A team led by Paul Brockway
at the University of Leeds, UK,
looked at 33 studies on the
economy-wide impact
of a phenomenon known
as the rebound effect.
First comes the direct
rebound: for instance, when
someone buys a more efficient
car, they may take advantage of
that by driving it further. Then
comes the indirect rebound:
fuel savings leave the owner
with more money to spend
elsewhere in the economy,consuming energy. This
contributes to the macro effect
of growing the overall economy.
Although the 33 studies used
different methods to model the
rebound effect, they produced
very consistent estimates of
its impact, leading the team to
conclude that the effect erodes,on average, 63 per cent of the
anticipated energy savings
(Renewable and Sustainable
Energy Reviews, in press).
“We’re not saying energy
efficiency doesn’t work. What
we’re saying is rebound needs
to be taken more seriously,”
says Brockway.
The idea that increased
efficiency may not deliver the
hoped-for savings dates back to
the Jevons paradox, named after
the economist William Stanley
Jevons who, in 1865, observed
that more efficient coal use led
to more demand for coal.
The last review of the
economy-wide rebound effectwas in 2007. The new analysis
is the first to pull together the
explosion of research since.
Worryingly, the influential
energy models that
governments and companies
rely on to examine how future
emissions and energy demand
may unfold aren’t good at
capturing the rebound effect.
The team looked at 17
scenarios from energy models,
including ones used by the
International Energy Agency,
the UN climate science panel,
BP, Shell and Greenpeace.
“Most of the models missed
out large numbers of the
channels which contribute
to rebound effects,” says Steve
Sorrell at the University of
Sussex, UK, a co-author of
the new study. One scenario
assumed a rebound effect
of just 10 per cent.
“The message is these
rebound effects do definitely
need to be incorporated in
any scenarios,” says Roger
Fouquet at the London School
of Economics.
If the rebound effect does
prove to be as big as suggested,
it means future global energy
demand will be higher than
expected and the world will
need far more wind and solar
power and carbon-capture
technology than is currently
being planned for.
But that doesn’t mean
nothing can be done to limit
the rebound effect. One answer
is to double down on energy
efficiency and do twice as
much to achieve the same
effect, says co-author Gregor
Semieniuk at the University
of Massachusetts Amherst. ❚WHO you eat with influences what
you eat, according to a study of
38 million food purchases at a
university campus over eight years.
Kristina Gligorić at the Swiss
Federal Institute of Technology
in Lausanne and her colleagues
tracked the eating habits of 39,
anonymised students and staff
between 2010 and 2018 through
smart card purchases on campus.
On average, people’s spending
was tracked for 578 days and they
visited shops, cafes, restaurants
and vending machines 188 times.
After monitoring people for a year
to find similarities, 830 strangers
were identified as “matched pairs”.
Their food purchases then deviated
as they respectively began to eat
with different friends.
Gligorić thinks of the matched
pairs as “doppelgangers whose
history is the same, but one by
chance happens to start eating with
someone who is a healthy eating
partner, and someone starts eating
with an unhealthy eating partner”.
Their spending was monitored
for change when they ate socially,
measured by when and where
purchases were made, ensuring
they were close enough to be in
the same queue as others. The
team found that people pick similar
items to the person they eat with.
If a new friend eats pizza, the tracked
person is more likely to eat pizza.
In comparison with the other
person in their matched pair, people
whose eating companions ate more
unhealthy foods bought an average
of one additional soft drink and
0.5 extra pizzas in the six months
after they buddied up. The same
happened with healthier food:
people who made friends with
healthy eaters bought an extra
5.71 healthy items and 1.13 fewer
unhealthy options on average over
six months (Proceedings of the ACM
on Human-Computer Interaction,
DOI: 10.1145/3449297). ❚Steel demand can
rise if production is
made more efficientNutrition Green technologyChris Stokel-Walker Adam VaughanSE
BA
ST
IANKAHNER
T/EPA
/SHUTTE
RS
TOCKClimate targets at risk
from efficiency paradox
Dining with healthy
eaters pushes you to
eat better food too
63%
of energy savings may be wiped
out by the rebound effect