Hank Morgan/Science Photo Library
energy system, but also undermine the environment
and climate essential to our future prosperity.
The transition to sustainable energy technologies
requires fundamental changes in the way we do business. Oil and emissions have become woven into the
fabric of our economy and society, thanks to fossil fuels’
unprecedented success in delivering cheap energy
when and where we need it. Changing these patterns
will involve major disruptions of business as usual. Fundamentally new ways of producing and using energy
are needed, and they will require massive amounts of
innovation in materials and chemical processes.
harm”. Burning fossil fuels releases pollutants such as
sulphur and mercury that endanger human health, as
well as greenhouse gases like carbon dioxide that
threaten climate stability. Some alternatives to fossil
fuels have their own degrees of potential harm, including the underground migration and leakage of sequestered carbon dioxide and the hazards of storing
spent nuclear fuel.
The third and most strict criterion for sustainability
is “leaves no change”. When the material outputs of
energy generation and use are recycled to replace the
inputs, the chemical cycle is said to be closed and the
chemical state of the world is unchanged. The process
of converting renewable energy sources like sunlight
and wind to carriers like hydrogen or electricity comes
closest to fulfilling this restrictive definition. Fossil
energy systems, in contrast, usually operate as once-through processes, irreversibly converting hydrocarbons to carbon dioxide and water. Some such systems
could, however, be retrofitted to collect and recycle the
combustion products to make new hydrocarbon fuel.
If this process used the Sun as its energy source, fossil
fuels, too, could meet this criterion.
Defining sustainability
Although most people agree that more-sustainable
energy technologies are desirable, they often find it
harder to agree on exactly how sustainable these technologies need to be, and even precisely what is meant
by sustainability. To clarify the debate, we suggest three
criteria for sustainability, each of which captures a different feature of the problem. While we do not have
the luxury of achieving full sustainability for all of our
next-generation energy technologies, we can use these
definitions to select our strategic sustainability targets
and track our progress toward achieving them. As
will become clear, the most sustainable energy technologies require the most challenging fundamental science breakthroughs (see figure on page 27).
The first criterion for sustainability is “lasts a long
time”. This quality has been a feature of many energy
sources we have used historically, including wood in
ancient times and oil throughout most of the 20th century. The definition of “long time” is, of course, relative: the world’s demand for energy long ago outpaced
the ability of wood to supply it, and the production of
oil is likely to peak sometime within the next few decades. Substantial reductions in the rate of oil consumption through higher-efficiency processes can
significantly impact on how long non-renewable resources last. In applying the “long time” criterion, we
need to distinguish between energy sources that are
effectively limitless and those that are finite but, for
the moment, adequate.
The second criterion for sustainability is “does no
Solar, wind and sequestration
Solar electricity comes close to satisfying all three criteria in the sustainability profile. In this electricity-gen-eration method, a solar photon strikes a semiconductor
photocell, excites an electron that travels through
transmission lines to be used for, say, lighting, transportation or information processing, before returning
At a Glance: Sustainability
● In order to be considered sustainable, an energy technology must last a long time,
do no harm and leave the environment unchanged
● The technologies that come closest to meeting these criteria are also those that will
require significant breakthroughs in materials science and processes to become
cost-effective or viable on a large scale
● The key to achieving such breakthroughs lies in making the transition from observing
materials and processes on the nano-scale to controlling these phenomena
● Biology is one source of inspiration for developing new technologies that are more
sustainable and that will help solve the energy–climate problem
