Sustainability and the Ehrlich equation
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Sustainability and the Ehrlich equation
A sustainable activity is one that is capable of It is self-evident that excessive levels of per-
going on for an indefinite period of time. sonal consumption and inefficient or dirty
technology are unsustainable.
Unfortunately, the term sustainable has been
widely abused, as illustrated by the com-
monly used contradiction sustainable growth:
growth can never be truly sustainable in a The quantity of resources we use
finite world. and our impact on the environment
effectively depend on three main
A simple example illustrates the concept of
factors:
sustainability: If reliable rainfall adds 100 litres
of rainwater to a tank every day, it is sustainable Population
to use up to 100 litres of this water per day. If the how many of us there are consum-
tank is large and is full to begin with, for a while ing resources and creating waste
it may be possible to use considerably more
than 100 litres per day. However, if the daily Affluence (consumption)
input from rainfall remains only 100 litres, even the average amount of goods and
starting with a full 10,000-litre tank, one can’t services we each use
use more than 100 litres per day sustainably.
The tank will eventually run dry. Technology
Human prosperity relies on a number of how inefficiently/harmfully we
resources and an environment that is eco- produce these goods and services
logically healthy. Even during the early devel- The Impact is the combination
opment of mankind, people consumed some of all three factors and it can be
resources. From time to time this may have summarised by what is known as
been locally unsustainable, but the impact was the Ehrlich or IPAT equation:
only local or, at worst, regional. Conversely,
I=PxAxT
since the industrial revolution, human activ-
ity, resource consumption and environmental
impact have grown relentlessly. We are now
using many resources at a greater rate than It is clearly impossible to be sustainable by
they can be replenished. As this continues, tackling just one or two of the IPAT factors in
the resources become exhausted and in some isolation. If any of the inputs to the equation is
cases irreversible damage is done to the envi- out of line – too much individual consumption,
ronment and its ecosystems. inappropriate technology or too many people
– the whole edifice of sustainability will
In the natural world, species that live unsus-
collapse.
tainably and exceed the carrying capacity
of their environment eventually experience a The key message spelt out by the IPAT equa-
rapid and often catastrophic crash in numbers. tion is that, even with very modest lifestyles and
If we don’t take measures to prevent it, sooner very good technology, human activity will still
or later this will happen to us. be unsustainable if the population is too large.
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Sustainability and the Ehrlich equation, contd.
The IPAT relationship has another impor- that all three factors in the IPAT relationship
tant message. Provided none of the individ- are addressed.
ual factors are too extreme, there are many
alternative versions of sustainable future
available to us. Let’s suppose that the most
environmentally friendly technology possible
is developed and put into practice (sadly not a We have the choice whether to live
foregone conclusion). Sustainable options will on a very crowded planet with people
range from the maximum possible number of at minimum subsistence standards of
people living at subsistence levels to a very living, or to opt for smaller populations
much smaller population living very comfort- and enough resources for everyone
ably. So long as the total impact of P x A x T is
to aspire to a good quality of life – and
not excessive, any of these alternatives would
more space for other species.
be sustainable.
For future generations to have a good quality
of life, it is essential that we humans ensure
Technology
Technology can be defined as ‘the practical distance it travels, and the resources impli-
application of science to commerce or indus- cated at the end of an item’s useful life, e.g.
try’ or ‘the discipline dealing with the art or how much energy is required to recycle pulp
science of applying scientific knowledge to from old newspapers.
practical problems’. In the context of sustain-
Technology uses a wide range of scarce or
ability, technology is the way that we convert
potentially scarce resources, including many
natural resources into real goods and serv-
that are non-renewable, such as rare metals
ices that we can eat, drink, wear, live in, travel
and fossil fuels. Others may be renewable but
on, etc.
only to a limited extent. For example, sustain-
Resource-efficient technology gives the great- ably managed forestry is only sustainable in
est benefit for the smallest input of resources quantities that can be supported by the land
over the full lifecycle of the ‘product’. This available without resort to non-renewable
applies to the resources needed to make the inputs.
goods in the first place, e.g. how much iron
ore and energy go into making a steel bridge, In many cases, it isn’t obvious to the con-
the resources needed to use the goods, e.g. sumer what resources go into making a par-
how much fuel a car consumes relative to the ticular product, cornflakes for example. Some
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Sustainability and the Ehrlich equation, contd.
manufacturers have already invested heavily Technology will continue to improve but it
in improving the resource efficiency of their is irresponsible to rely on technology that
technology and supply chains. Others could hasn’t yet been practically proven. Some new
still do much better. But even with the best technologies which few of us even dreamed
available technology, an industrial way of life about a decade or two ago are already in
is inevitably resource-intensive. widespread use; others, long considered to
be ‘just round the corner’, still seem no nearer
The environmental impact of waste is a
to fruition, a prime example being technically
consideration for many types of technology.
and economically viable nuclear fusion power.
This applies to the waste from manufacturing
However important it undoubtedly is to deve-
processes themselves, packaging, products
lop more efficient and appropriate technology,
that are surplus to requirements, such as
the inescapable conclusion is that this on
excess food, and items that are worn out,
its own will be insufficient to assure us a
broken-down, technologically obsolete or
sustainable and prosperous future.
otherwise no longer useful. Finally, what
happens to the manufacturing equipment
itself when it is no longer required?
Many companies are now making major
efforts to minimise waste and to recycle end-
Using the best available technology
of-life materials and equipment. Indeed, some
are designing their products to be easier to will help reduce human impact on
recycle and to be less harmful if they do end the environment but technology on
up in the environment. But this is not always its own is not enough to make us
easy and recycling often incurs additional sustainable.
energy demand.
The IPAT equation shows clearly:
The overall message is that whereas industri-
ally developed technological economies still • we need to reduce our
need to improve the efficiency of the technol- individual consumption.
ogy they employ, the law of diminishing returns
• we need to stabilise our
applies. It will become increasingly difficult to
populations at sustainable
manufacture and supply goods using progres-
sively smaller amounts of resources: levels.
• technology can only ever improve as far
as the laws of physics allow.
• renewable resources, including energy,
are only renewable to a limited extent
and are often expensive to harness.
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Sustainability and the Ehrlich equation, contd.
Affluence (consumption) maintain the status quo longer term. Not only
Many environmental campaigners exhort us are large disparities between rich and poor
to adopt simpler lifestyles in order to save the inconsistent with human rights but almost
planet. They are of course correct. Many of inevitably they eventually lead to conflict.
the goods and services we use do relatively
Even within individual nations, too wide a
little to enhance our lives, whilst having a dis-
spread between rich and poor makes it very
proportionate impact on the environment.
difficult to moderate consumption. The combi-
Unfortunately many people do not see fit to nation of celebrity culture and mass consumer
moderate their own lifestyles for the sake of marketing encourages people to aspire to life-
posterity. These include ‘enviro-sceptics’ who styles beyond the resources available. We
do not acknowledge that an anthropogenic do not advocate poverty as a way of life; on
environmental and resources crisis is looming the other hand, there is evidence that once
and ‘techno-fixers’ who believe that better peoples’ basic needs have been met, relative
technology is a panacea for all environmental affluence (their perception of themselves as
problems. being better or worse off than others) usually
has more effect on their sense of well-being
Although Population Matters stresses the
than their absolute standard of living.
importance of population size, we do also
believe that individuals in economically devel-
oped countries need to moderate their life-
styles and that these countries as a whole
must be more frugal in their use of resources
in order to protect the environment. One Reduced levels of personal consump-
way to achieve this might be to apply the tion are a necessary step towards sus-
Contraction and Convergence concept pro- tainability, but we would need to return
posed as an equitable basis for rich countries to minimum subsistence lifestyles for
to restrain their consumption in an increas- this to be sufficient on its own. For a
ingly resources-constrained environment. decent quality of life the other two
factors in the IPAT equation must also
It is completely unsustainable for the whole be taken into account:
world population to enjoy high-consumption
western lifestyles. Global Footprinting Network • the most environmentally efficient
data show that between three and four planet technology needs to be made
earths would be needed to support the exist- available and applied on a world-
ing world population at the present per-capita wide basis.
consumption levels of the UK. It is unrealis- • population numbers, globally
tic to expect better technology to overcome a and for individual countries, need
deficit on this scale. to be stabilised and fall to levels
which can be supported at decent
Clearly it is unethical for rich countries to insist
standards of living for everyone.
on maintaining consumption levels that are
impossible for other peoples to attain. Even if
this were not the case, it is still unrealistic to
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Sustainability and the Ehrlich equation, contd.
Population size • larger amounts of energy are required for
Every person consumes resources and there- cooking, heating and industrial activity
fore has an impact on the environment. • greater demand for resources increases
However modestly we live, we still have to eat, the likelihood of conflict
we need access to fresh water and inevitably • there is less margin to survive changes in
we create some wastes. Complex industrial the environment, be they climate change
societies consume a wide range of resources or natural disasters such as earthquakes
and cause large amounts of waste. The more and flooding.
resources that a community consumes per
head of population, the greater its impact and It is still possible for communities to be too
therefore the smaller the total population that small. If numbers are too small, there may be
is sustainable: too few people to undertake major projects
or for culture, art and science to prosper. We
• people take up space and consume believe that present populations far exceed
resources that are needed for other living this minimum in most countries of the world.
species
There is therefore an urgent need to stabilise
• therefore fewer people would mean more
populations and gradually reduce them to
habitat for wildlife and fewer species
numbers consistent with decent lifestyles for
being driven to extinction
all.
In the early days of humankind, people banded
together to ensure survival. More people meant
better ability to defend the community and
more brainpower to solve problems. This may The IPAT equation shows that we
be one of the reasons why so many cultures have a choice about the world our
have a deeply in-built bias favouring fertility descendants will inherit:
and birth. In the twenty-first century, however, • a high population, crowded world
most human populations are too large rather with a low quality of life and low
than too small. Finite amounts of land, water life expectancy or
and energy resources have to be shared out
between increasing numbers of people and • a less populous world with a
the amount available for each individual gets good quality of life for all.
smaller. The choice is ours.
More people means:
• more food and water are required to
sustain the population Read more about Carrying capacity and
• more land is required on which to grow BioCapacity and Ecological Footprint.
food These concepts and tools play an important
• more raw materials are needed to provide part in helping us quantitatively to understand
clothing, shelter and other manufactured the relationship between our numbers and our
goods sustainability.
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