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Publicize or perish

The fate of the next 50 generations may well be determined in the next few months and years. Will the US Congress agree to a shrinking cap on greenhouse-gas emissions and legislation to achieve the transformation to clean energy? If not, you can forget about a global climate deal. But even if the bill passes and a global deal is achieved, both will need to be continuously strengthened in coming years, as the increasingly worrisome science continues to inform the policy, just as in the case of the Montreal Protocol on ozone-depleting substances.

The International Scientific Congress on climate change held in Copenhagen in March, which was attended by 2000 scientists, concluded that “Recent observations confirm that, given high rates of observed emissions, the worst-case Intergovernmental Panel on Climate Change (IPCC) scenario trajectories (or even worse) are being realized.” That would mean that by 2100 there would be atmospheric concentrations of carbon dioxide of more than 1000 ppm, total planetary warming of 5 °C and sea-level rises probably on the high end of recent projections of 1–2 m followed by a rise of as much as 2 cm per year or more for centuries. We would also see one-third of inhabited land reaching dust bowl levels of aridity, half or more of all species becoming extinct, and the oceans increasingly becoming hot, acidic, dead zones. And if we do not change course quickly, the latest science predicts that these impacts may be irreversible for 1000 years.

In short, the fate of perhaps the next 100 billion people to walk the Earth rests with scientists (and those who understand the science) trying to communicate the dire nature of the climate problem (and the myriad solutions available now) as well as the ability of the media, the public, opinion-makers and political leaders to understand and deal with that science.

Disinformation and scientific illiteracy

So far, we are failing miserably. Neither the US nor the world as a whole has taken any consequential action to reverse emissions trends. And if the scientific community does not help lead the way in reversing emissions, then we will justifiably bear serious blame from future generations, who will no doubt become increasingly bitter about the havoc our ignorance and myopia has brought them. Nobody will be writing books calling us “the greatest generation.”

As one example of how bad scientific messaging has been, let me go through Gallup polling over the past decade as discussed in a 2008 article in Environment magazine entitled “A widening gap: Republican and Democratic views on climate change”.

The article reported that in 1997 some 52% of Democrats said that the effects of global warming had already begun and 52% said most scientists believe global warming is occurring. In 2008 some 76% said warming had begun and 75% said most scientists believe warming is occurring. It would appear that Democrats believe most scientists.

Few leading climate scientists or major scientific bodies would disagree that the scientific case that the planet is warming – and that humans are the dominant cause of recent temperature rises – has become stronger in the past 10 years. That is clearly seen in the scientific literature – as summarized in the IPCC reports.

And yet for Republicans, in 1997 some 48% said warming had begun and 42% said most scientists believe warming is occurring – a modest six-point differential. By 2008, the percentage of Republicans saying the effects of global warming had already begun had dropped to a mere 42% (an amazing statistic in its own right given the painfully obvious evidence to the contrary). But the percentage saying most scientists believe global warming is occurring had risen to 54% – a stunning 12-point differential.

In short, a significant and growing number of Republicans – one in eight as of 2008 – simply do not believe what they know most scientists believe. That is quite alarming news, given that it is inconceivable that the US will take the very strong action needed to avert catastrophe unless it comes to believe what most scientists believe, namely that we are in big, big trouble and can delay no further.

Here is the lesson for scientists: in the last decade, we have apparently become less convincing to Republicans than the deniers have been. They have apparently become better at messaging, while we have perhaps become worse.

In part, this has occurred because there is an organized disinformation campaign promoted by conservative think tanks like the Competitive Enterprise Institute and well funded by fossil-fuel companies like ExxonMobil, with key messages repeated by conservative pundits and politicians like George Will, Rush Limbaugh and Republican Senator James Inhofe. At the same time, the media have treated this more as a political issue than a scientific one, thereby necessitating in their view a “balanced” presentation of both sides, notwithstanding the fact that the overwhelming majority of scientists understand humans are warming the planet and dangerously so. Also, increasingly profit-driven media have been abdicating their role in science education. Science writer Chris Mooney and scientist Sheril Kirshenbaum offer these grim statistics in their recent book Unscientific America: How Scientific Illiteracy Threatens our Future (2009, Basic Books):

For every five hours of cable news, one minute is devoted to science;
Some 46% of Americans believe that the Earth is less than 10,000 years old;
The number of US newspapers with science sections has shrunk by two-thirds in the last 20 years;
Just 18% of Americans know a scientist personally;
The overwhelming majority of Americans polled in late 2007 either could not name a scientific role model or named “people who are either not scientists or not alive”.

The lack of scientific messaging

Yet just when the media are abandoning science coverage, many scientists are increasingly reluctant to address politicized issues like global warming.

Scientists who are also great public communicators, like Carl Sagan or Richard Feynman, have grown scarcer as science has become increasingly specialized. Moreover, the media like the glib and the dramatic, which is a style that most scientists deliberately avoid. Scientists like to focus on the things that they do not know, since that is the cutting edge of scientific research. So they do not keep repeating the things that they do know, which is one reason that the public and the media often do not hear from scientists about the strong areas of consensus on global warming. And as the physicist Mark Bowen writes in Thin Ice (2006, Holt), his book about glaciologist Lonnie Thompson, “Scientists have an annoying habit of backing off when they’re asked to make a plain statement, and climatologists tend to be worse than most.”

As scientist and writer Jared Diamond wrote in a 1997 article in Discover magazine on scientific messaging (or the lack thereof), “Scientists who do communicate effectively with the public often find their colleagues responding with scorn, and even punishing them in ways that affect their careers.” After Sagan became famous, he was rejected for membership of the National Academy of Sciences in a special vote. This became widely known, and, as Diamond writes, “Every scientist is capable of recognizing the obvious implications for his or her self-interest.”

Scientists who have been outspoken about global warming have been repeatedly attacked as having a “political agenda”. As a 2006 article in the Bulletin of the American Meteorological Society explained (87 1025), “For a scientist whose reputation is largely invested in peer-reviewed publications and the citations thereof, there is little professional pay-off for getting involved in debates that mix science and politics.”

The scientific community must figure out how to effectively engage the public on this crucial issue. The physics community in particular must help lead the way. After all, it was effective at warning the public and policymakers about the dangers of that other existential threat to the human race – nuclear weapons. We appear to have walked back from the precipice of global nuclear war only to face an equally grave threat from our unbridled consumption of fossil fuels.

I believe that the major scientific bodies and leading scientists in the US must come together immediately to develop and quickly implement a serious communication strategy. We are again at the precipice. Indeed, it is, as the current Presidential Science Advisor and physicist John Holdren has said many times, too late to avoid dangerous anthropogenic warming of the planet. Now the only question is whether we can avoid unmitigated catastrophe.

One final point. If the scientific community is unable to help persuade the public, opinion-makers and political leaders to take the necessary action now, then the entire relationship of science to the broader world will change forever. When the US and the world do get desperate about global warming in the next decade or two, then the entire focus of society, of scientists and engineers, and of academia will be directed toward a Second-World-War-scale effort to mitigate what we can and adapting to the myriad miseries that our myopic dawdling has made inevitable. I do not think that the scientific community has even begun to think about that.

Sustainability made simple

It is not often that a physics book becomes a publishing phenomenon; and when it does happen, the book is usually about strings or cosmology. But David MacKay’s Sustainable Energy – Without the Hot Air is different. It tackles a down-to-earth but controversial subject in a remarkably even-handed manner; it has been lauded by a number of national and international publications; and it remains high in the bestseller lists even though it is free to download.

Despite the trendy word “sustainable” in its title, this is avowedly not a book about climate change, nor is it a political polemic. Instead, its primary purpose is to give decent numerical estimates of the UK’s future energy production and consumption after the oil runs out. Such estimates are normally only found together in think-tank reports, where they can appear surprisingly frail: their underlying physics is seldom revealed, and it is difficult to judge their validity. The mainstream media, on the other hand, rarely seem to use large numbers competently. This book, with its slogan “numbers not adjectives”, is an attempt to bridge that gap.

MacKay, a physicist at Cambridge University who has just been named as the UK government’s scientific advisor on energy and climate change, begins by choosing a single unit for power consumption: kilowatt-hours per person per day, rather than the usual muddle of kilowatt-hours, litres, BTUs, barrels, tonnes and so on. Though at first this seems clumsy, it turns out to be rather effective. Figures mostly fall in the range 1–100, and results are easily translated into personal terms. With this technical detail firmly in hand, MacKay then builds up two stacks: a red stack for energy consumption and a green stack for sustainable energy generation.

If one accepts a need to balance current energy consumption with generation, then conclusions emerge quite clearly, and the book summarizes these in a straightforward manner. Renewable energy takes up a lot of land, and, for the UK, only wind over our coastal seas and solar power from other people’s deserts can provide us with significant amounts of it. Nuclear power may be problematic, even dangerous, but it could meet much of our needs; compared with the alternatives, the volume of waste it produces is small. On the domestic side, building insulation needs to be improved and heating needs to be electrified, probably by the extensive use of air-source heat pumps.

MacKay uses an additional unit – kilowatt-hours per 100 passenger-kilometres – when discussing transport, and this illuminates his comparison of the energy demands of different modes of travel. Here again, the likely advantages of electrifying as much of our transport infrastructure as possible become clear; in the absence of a persuasive “green” alternative like hydrogen cells, no other option offers the flexibility of electricity. The author is at pains not to let politics intrude on his message, and the book concludes with a range of “energy plans” to suit all political tastes – except head-in-the-sand failure to acknowledge that there is a problem.

However, setting energy policy aside, the book also works on a deeper level, bringing the concept of energy home to physics through “back-of-the-envelope” calculations. MacKay shows how a physicist initially approaches a problem by identifying processes and constraints, and getting numerical estimates of them.

Naturally, such estimates need to be refined, but they make a good starting point – as many physicists will know from their own lunchtime conversations. For example, we recall a discussion about recycling in which we needed to know the conversion rate of hydrocarbon fuel mass into energy. For an immediate rough estimate, we used the calorie content of butter – and indeed this same calculation appears alongside a picture of a pat of butter on page 29 of the book. The butter-derived figure proves to be about 20% too low – but since one of us developed instruments to measure the moisture content of butter, we are able to improve the estimate by eliminating this moisture mass (which, of course, contributes no energy) from the calculation.

Of course, some estimates in the book are intended only to be good to within a factor of two or so, and occasionally somewhat poorer, since MacKay’s goal is often just to put a rough upper bound on a potential source of energy. His estimate of tidal-stream power, for instance, combines physical arguments with a perusal of the tidal charts in a nautical almanac, and seemed to us (as yachtsmen) to rather underestimate the ubiquity of strong tides around the UK’s coast. Such an approach does open the book to criticism, particularly from specialists; indeed, it could easily become a victim of its own success if policymakers and others begin to regard its figures as accurate final judgments. That would be a shame, for it would traduce one of the book’s intentions, which is to enable readers to do their own calculations – in fact, its original working title was “You go figure it out!”.

To this end, MacKay is very keen that the book should be digestible. It is well illustrated, and all algebra is confined to the technical chapters (in effect appendices) that make up the last 90 or so pages. The physicist will find much that informs (and occasionally amuses) in these chapters, particularly in those on cars and planes. The former runs a long way on very little algebra, and in the latter the basic physics of a jumbo jet’s energy consumption is shown to scale down quite well to fit an albatross.

In the main text, however, all that is needed is basic numeracy and familiarity with exponential notation. For this reason the book would be a good way of introducing teenagers to how real physicists work – all the more so because MacKay’s treatment of energy is much more positive and empowering than either the school physics curriculum or most environmental literature. By exposing both the data from which his book’s conclusions are drawn, and the methods and arguments by which they are reached, MacKay in effect says “You need take no one’s word for it. You can work it out for yourself, and this is how.” Various reviewers have said something along the lines of “every policy maker should read it”. We would rather advocate it as a book every budding physicist should read – and perhaps also as the one every working physicist would like to have written.

Wrong but useful

A quick tour of the Internet reveals some very strong feelings on the subject of climate models. Unsurprisingly, on climate contrarian sites, such models are described in all sorts of unflattering terms and dismissed out of hand as fundamentally useless. However, in more rational forums, and sometimes even among scientists themselves, one occasionally comes across a basic ignorance of whether climate models are any good, and, even more importantly, what they are good for. By the time one gets to policymakers, climate models are seen at best as black boxes, and at worst as simply irrelevant to their detailed concerns. However, climate models – appropriately used – might have a vitally important part to play in breaking through some of the log jams now hampering policymakers.

The complexity of climate

Models of any stripe are simply quantitative or numerical expressions of the theories we have for how the real world works. Climate models encapsulate what we know about how the Sun’s rays travel through the atmosphere and how heat from the surface of the Earth gets absorbed by clouds, water vapour and, of course, carbon dioxide. They contain sophisticated (though imperfect) representations of cloud formation and rainfall, floating sea ice and ocean turbulence, rivers and lakes, and soil and vegetation. Each representation is based on direct observations of the processes in question and is tested against many different constraints. The models (and there are many) have numerous common behaviours – they all cool following a big volcanic eruption, like that at Mount Pinatubo in 1991; they all warm as levels of greenhouse gases are increased; they show the same relationships connecting water vapour and temperature that we see in observations; and they can quantify how the giant lakes left over from the Ice Age may have caused a rapid cooling across the North Atlantic as they drained and changed ocean circulation patterns.

This gives us a hint: models are useful for tying together causes and effects in complex systems where answers are often only obvious in hindsight. We can apply them for climate changes in the past – global changes in temperature or rainfall patterns inferred from the paleoclimate data for instance – and help attribute events to causes. Indeed, the attribution of any particular climate trend or set of events is inherently a model-based exercise. Without a way of telling the difference that any particular cause might have, how can we recognize its fingerprint in the real world? This is the basis of the conclusion of the Intergovernmental Panel on Climate Change (IPCC) that human activities are behind the rise in global temperature in recent decades.

Show and tell

The other use is in helping chart the course of the future. People are quick to dismiss model projections of climate as being inferior to observations, but as Tom Knutson and Robert Tuleya, from the Geophysical Fluid Dynamics Laboratory at Princeton University and Old Dominion University, Virginia, pointedly noted in 2005, “If we had observations of the future, we obviously would trust them more than models, but unfortunately observations of the future are not available at this time.”

However, prediction is hard, particularly of the future (to paraphrase Niels Bohr). For the climate, there are two kinds of possible predictability. The first is based on extrapolating seasonal and interannual changes based on precise knowledge of today’s state of the atmosphere and ocean combined with an understanding of how the various modes of variability in the ocean might develop. Whether these efforts can provide useful information on regional climate on year-to-year and longer timescales is currently being explored. The more usual source of predictability, however, is considering the long-term changes related to increases in greenhouse gases, a volcanic eruption or other changes in the composition of the atmosphere. The first relies on a thorough understanding of patterns like El Niño or the North Atlantic ocean circulation, while the second tries to average over that variability to predict changes in the mean state.

For this second kind of prediction, you always need a scenario for what might happen to the drivers of climate change. Will carbon dioxide concentrations continue to increase? Will air pollution continue to decrease in the developed world but increase in the developing world? How fast will tropical deforestation progress? These scenarios are highly dependent on economics or political decisions and so qualify easily for the “hard prediction” category. Nonetheless, economists do their best to make a range of reasonable estimates for plausible futures and calculate the resulting changes in emissions.

But climate is complex. There are multiple causes, giving rise to multiple effects such that the interactions among the various components – like low-level ozone, aerosols (airborne particles) and clouds – can get hideously complicated. Ozone near the ground is created from the soup of emissions from car exhausts, factories and fires, and it is a public-health problem as well as a greenhouse gas. Aerosols too can come from multiple sources: sulphur-dioxide emissions from coal-burning power plants produce sulphate aerosols in the air; black carbon (soot) and organic-carbon aerosols come from incomplete combustion of biomass and even from the complex organic molecules emitted by plants. They all interact directly with the Sun’s radiation to either block it (for sulphates) or increase absorption (black carbon). They also have indirect effects by changing how easy it is for clouds to form, or by changing how reflective snow is (black carbon effectively makes the snow dirtier).

Solving the puzzle

Science, however, has made tremendous progress by trying to break things down into their component parts. Thus, we have traditionally studied the impact of carbon dioxide separately from the impact of sulphate aerosols and separately from the impacts of the emissions that cause ozone (the “precursors”). Frequently, these studies are carried out by separate scientists, in separate institutions under separate grants and with separate goals. While this has led to a great deal of insight, it has also tended to divorce the science from policy.

Let me give some examples. In the last IPCC report there is an iconic figure that shows the magnitude of the effects on climate for the 20th century. Carbon dioxide is the largest warming factor, followed by methane, nitrous oxide, low-level ozone and black carbon. On the cooling side, there are sulphate and nitrate aerosols and land-use changes. There is nothing wrong with this picture, but how helpful is it in deciding what to do about the power generation in China that produces carbon dioxide but also sulphates, or for assessments of mileage standards that will affect ozone precursors, black carbon from diesel exhaust as well as gasoline use? In each case, we have mixed results for the climate and potential impacts on other public-policy issues as well (air quality for instance). Because of scientists’ focus on single-factor experiments (change carbon dioxide, or change black carbon, or change sulphates), we have not historically provided enough information for policymakers to properly weigh up these different effects. Neither have we clearly identified the key sectors around the world that might provide win-win-win scenarios for people worried about climate, air quality and ecosystems.

Finely honed

However, scientific and computational advances in climate modelling and validation over the last few years now mean that we can do a much better job. Models now include many more of the interactions that matter: atmospheric chemistry that can predict ozone concentrations as a function of the methane or carbon-monoxide precursors; or aerosol physics for multiple kinds of particles – those directly emitted, like soot and mineral dust, and those created in the atmosphere from other emissions. More importantly, the models now include myriad interactions: the chemistry that takes place on the surface of dust aerosols that in turn affects sulphates; the impact of increasing methane on atmospheric oxidation, which affects aerosol concentrations; or the affects that aerosols have on clouds or snow albedo.

We can therefore now start to directly answer the questions that policymakers are raising – and some of the results may be surprising.

In Europe, for instance, the use of coal for power generation produces very little sulphate aerosol or black carbon because of existing air-quality controls. Thus, the only options for reducing the climate impact of coal relate to specific reductions in coal burning or investment in carbon capture and sequestration.

However, in India and China a lot of coal and biomass is burned in domestic settings where inefficient low-temperature combustion and a lack of pollution controls mean that the mix of emissions is much more complicated – carbon dioxide, of course, but also large amounts of carbon monoxide, black carbon and sulphates. Together, these emissions contribute strongly to the “Atmospheric Brown Cloud” phenomenon and to the appalling air quality in the region. This implies that efforts to improve rural electrification for instance – even if the power is generated in a modern coal power plant – could still reduce net climate warming because of the impacts on reducing ozone, methane and black carbon. These kinds of strategies are already being pushed by the Indian government because of the more direct impact on indoor and regional air quality and to reduce the deforestation associated with biomass collection, but a recognition of the net climate impact may help bridge the current gaps in the international negotiations on a climate treaty.

Other surprises include the recognition that reducing methane emissions from whatever source has important indirect impacts on a range of other drivers and is a more effective strategy for short-term reductions in global warming than had been previously recognized. As we move forward, we should be able to assess the net climate impact of any particular policy given the changes in emissions that will result.

Like a full life-cycle analysis for judging the impact on net emissions of a switch in energy-generation technologies, a full Earth-system analysis should become the new standard in judging climate-policy proposals.

All climate models are wrong, but some of them are useful, and by working more closely to answer the questions that are actually being posed by policymakers, we can make them more useful still.

The road to sustainability

The oil shock of the 1970s triggered worldwide awareness of oil dependency and launched a search for alternative sources of energy. But three decades on, these efforts have barely had an impact: oil still accounts for almost 40% of global energy use, and fossil fuels make up 85%. The US, for example, imported 20% of its oil in 1970; today the figure is 60%, and other countries import even larger fractions of the oil they consume. The problem of oil dependency is compounded by cost. Before the current recession, the price of oil peaked at $140 a barrel – five times its price in 2002 and 10 times its price in 1976 – rewriting the economics of transportation, food, manufacturing and trade that underlie the operation of society. In addition to dependency and cost, energy security is a pervasive threat. The concentration of oil production in a few regions of the world makes the supply of oil vulnerable to unpredictable events such as weather, terrorism, and geopolitical manoeuvring. Because oil provides so much of our energy, severe reductions in its flow would dramatically change the way we live.

The current outlook for energy adds a crucial new dimension that was not present in the first oil shock: carbon-dioxide emissions and climate change. The Intergovernmental Panel on Climate Change has documented global warming through rising sea levels, shrinking snow cover in the northern hemisphere and higher surface temperatures. These increases in temperature track similar increases in the concentration of carbon dioxide in the atmosphere – a remarkable correlation that extends over four ice ages covering the last 400,000 years. Carbon-dioxide levels are now 30% higher than they were before the Industrial Revolution, and they are rising at an accelerating pace, driven by the human combustion of fossil fuels. The potential implications for global warming and climate change are sobering. Left unchecked, climate change could produce dislocations in the agricultural, trade and demographic patterns that define global economic and social structures.

A particularly worrying feature of global warming is the timescale involved. It takes 400–1000 years for carbon dioxide in the atmosphere to equilibrate in the deep ocean. Hence, the carbon dioxide that we have already added – and continue to add – to the atmosphere will affect not only our grandchildren but also their grandchildren and many generations beyond. The long-term impact of global warming requires a sustained investment of intellectual resources to understand the dynamics of climate change, rather than the short-lived interest and spending surge that followed the oil shock of the 1970s.

Where the energy goes

The dual challenges of energy and climate are captured in a single term: sustainability. Our current reliance on oil and other fossil fuels (see “Where the energy goes”) and our unfettered emission of carbon dioxide to the atmosphere are not sustainable activities. We are using oil and fossil fuels at far greater rates than nature creates them, and their cost and supply are fragile and volatile. Our carbon-dioxide emissions are growing by 22% per decade and they threaten to overwhelm the ability of the ocean–atmosphere system to absorb them and maintain a stable climate. These activities not only deplete the fossil resources required for our current 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. Fun_damentally new ways of producing and using energy are needed, and they will require massive amounts of innovation in materials and chemical processes.

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 tech_nol_ogies require the most challenging fundamental science breakthroughs (see “Making the grade”).

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 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.

Solar, wind and sequestration

Solar electricity comes close to satisfying all three criteria in the sustainability profile. In this electricity-generation 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 to the photocell, where it replaces the hole left by the original electronic excitation. Once completed, the electron round trip does no harm and leaves no chemical change. However, although solar electricity may be fully sustainable in operation, it is not necessarily fully sustainable in the construction or disposal of its infrastructure – both steps require energy and emit carbon dioxide. These often-ignored full-life-cycle issues must be considered when evaluating the sustainability of energy technologies.

Making the grade

Despite the appeal of solar electricity, serious technical challenges block its widespread deployment. Before the reach of solar electricity can expand, its costs must fall below those of fossil electricity and must be low enough to attract the majority of future demand growth without artificial incentives. Achieving this will require breakthroughs in understanding and controlling the fundamental nano-scale phenomena of photo_excitation, charge separation and charge transport in, for example, high-efficiency multijunction solar cells and in low-cost organic and thin-film solar cells (see pp40–45, print edition only). An even greater and less-explored challenge is utility-scale electricity storage to bridge the day–night and cloudy–sunny cycles. Without the ability to store electricity, solar power can never be more than a supplement to fossil energy generation.

As a derivative of solar energy, wind electricity shares its sustainability profile, with the potential to satisfy all three criteria. The barriers to wind electricity are cost, utility-scale storage of electricity to bridge calm days and long-distance transmission capacity to deliver wind energy from its remote sources to urban population centres. The output of wind turbines is limited by the weight of the generator that can be supported on the tower. Superconducting generators can, however, lower the cost and land area required for wind electricity by a factor of two because they produce twice the output but are the same size and weight as conventional generators.

As for fossil-fuel electricity plants, they can be made more sustainable by capturing their carbon-dioxide emissions and sequestering the gas in underground geologic formations. Carbon sequestration prevents the carbon dioxide from entering the atmosphere – a positive step toward “doing no harm”. This positive step is balanced, however, by the challenges associated with injecting the carbon dioxide underground. We know little about how carbon dioxide reacts with the porous rocks in which it would reside, and less still about how far it might migrate during the thousands of years it must remain there. Carbon dioxide is supercritical under sequestration conditions, and the high temperature and pressure alter its reaction chemistry and enable it to diffuse quicker through porous rocks. These primary scientific challenges require a host of studies of surface-reaction chemistry to identify reaction pathways, intermediate species, chemical kinetics and diffusion phenomena under simulated sequestration conditions.

Beyond reaction chemistry, techniques for monitoring and modelling the migration of large quantities of supercritical carbon dioxide are also needed, so that we can anticipate where and how far it might travel over the thousands of years it must remain underground. The potential for contaminating an aquifer or finding an escape route to the atmosphere must be thoroughly understood for every sequestration site. Leakage is indeed one of the biggest challenges. A sequestration system with a leak rate of 1% per year exhausts all the carbon dioxide stored in its first year of operation in just a century – a blink of an eye on the timescale of ocean–atmosphere dynamics. During release, heavy carbon dioxide can displace lighter oxygen in low-lying areas, possibly leading to the suffocation of people and animals, as happened in a catastrophic incident at Lake Nyos, Cameroon, in 1986.

From a sustainability perspective, sequestration allows us to use the Earth’s coal resources (which will last longer than oil, though not as long as the Sun) with reduced harm to the atmosphere. Storing carbon dioxide underground, however, carries potential risks of contamination and leakage that are largely unexplored. Sequestration also leaves clear chemical changes as coal is removed from the Earth and carbon dioxide is injected.

The nuclear options

Like carbon sequestration, nuclear electricity keeps greenhouse gases out of the atmosphere, and thus represents a step towards sustainability. Next-generation reactors based on new materials could last longer than reactors designed in the 1960s – typically 80 years or more instead of 60 – and can turn 50% of the heat produced by fission into electricity, compared with 32% for existing reactors. Higher efficiency also allows the uranium supply to last longer; this, together with longer lifetimes, reduces the number of nuclear plants that will need to be built. These increases in efficiency can be achieved by operating reactors at higher temperatures (1000 K instead of the current 650 K) and at neutron fluxes an order of magnitude higher than the current values of 4 × 10¹³ n cm^–2 s^–1. However, at such high temperatures and fluxes, chemical corrosion is an additional serious challenge. Next-generation reactors will require a new generation of “extreme materials” that can not only survive, but also function under the triple extremes of high temperature, high neutron flux and aggressive chemical corrosion. Advanced ferritic steels hold promise in these environments; developing them by design rather than serendipitously will accelerate deployment significantly.

A long way to go

The scientific challenge for next-generation extreme materials – whatever their composition – is to understand their failure modes, and to prolong their useful lifetimes by interrupting or arresting these failures. Damage starts with atomic displacements that create interstitials and vacancies, which then migrate and aggregate to form clusters and ever-larger extended structures. Eventually, the damage reaches macroscopic dimensions, leading to degradation of performance and failure. This problem is massively multiscale, covering nine orders of magnitude in its spatial dimension, and neither experiment nor theory has yet captured this complexity in a single framework.

On the experimental side, in situ measurements of neutron irradiation with atomic or nano-scale resolution are needed to observe the initial damage processes, followed by coarser-grained experiments to capture migration, aggregation and ultimately macroscopic failure. The modelling challenge is equally dramatic: kinetic energy from an incident particle is transferred successively to electronic, atomic, vibrational and structural systems, requiring a diverse mix of theoretical formulations appropriate for different spatial scales.

To create new extreme materials that operate effectively in reactor environments we will have to go beyond observation and modelling to controlling the evolution of defect structures and interrupting their development before they can degrade performance. Introducing designer interfaces that collect and trap nano-scale defects before they cluster is one strategy for making materials defect-tolerant or self-healing. Treating defected regions with targeted photon or particle beams to anneal out the damage before it grows beyond a critical size is another. Although developed for nuclear applications, next-generation materials with these features should find wide application in other areas, including high-temperature turbines and coal-fired boilers, thus bringing overall energy efficiency closer to thermodynamic limits.

The sustainability profile of nuclear electricity shares many qualitative features with carbon sequestration. Like coal, terrestrial uranium resources will last a few hundred years, longer than oil but not as long as the Sun, and nuclear reactors emit no carbon dioxide into the atmosphere. The threat to the atmosphere is, however, replaced by a new potential danger: spent fuel that must be stored, perhaps underground, for hundreds or thousands of years to reduce its radiation level by natural decay. Developing fuels that fission a larger fraction of the available nuclei in a fuel rod – the current average is 4% – would mean that uranium supplies would last longer, and that the storage requirements for spent fuel would be less. Still, nuclear waste, like sequestered carbon dioxide, has the potential to leak, threatening water supplies and human health. New methods of treating, containing, monitoring and modelling nuclear waste are needed. Finally, like fossil-fuel electricity, nuclear electricity leaves substantial chemical change by removing uranium from the Earth and replacing it with radioactive waste.

Fusion electricity is more sustainable than fission because it replaces hazardous heavy-element fuel with benign, light and abundant hydrogen. The fusion product, helium, is likewise kind to the environment and climate. The fusion process, however, is even more extreme than fission, requiring neutron fluxes approximately 100 times greater than in fission reactors. Designing materials to withstand these exceptional irradiation conditions is a major scientific challenge.

Biofuels and electric cars

Replacing conventional oil with biofuels has the potential to achieve greater sustainability by recycling carbon dioxide and enabling fossil resources to last longer. However, it is now generally accepted that the energy balance and carbon footprint of corn ethanol and gasoline are only marginally different. In terms of lasting a long time and doing no harm, therefore, the two are approximately equally sustainable. Cellulosic ethanol made from the stalks and leaves of plants offers more hope. The scientific challenge for cellulosic ethanol is to discover or design a better chemical-conversion route from cellulose, nature’s evolution-hardened construction material, to fermentable sugar or liquid fuel. The known chemical and enzymatic routes are too expensive and inefficient to be competitive. Biofuels from algae offer an alternative route, since cultivating algae requires far less land than other biofuel crops, but a cost-competitive conversion route is not yet available and the science is still in its infancy.

Recycling carbon dioxide and water to produce fuel can also be done without biology, by using concentrated solar heat to drive high-temperature thermochemical reactions or electronic excitation from solar photons to drive photochemical reactions at room temperature. Both routes face materials challenges, and neither is scientifically ready to deploy. Thermochemical recycling requires advanced hybrid materials that can physically withstand and chemically promote the targeted reactions at high temperatures, and photochemical recycling requires new cost-effective catalysts that split carbon dioxide and water to drive the synthesis of hydrocarbon fuel. These challenges are firmly in the realm of discovery. Overcoming them will require use-inspired basic research (see “From observation to control”).

The sustainability profile of recycling carbon dioxide through biofuels (other than corn ethanol) and thermochemical or photochemical cycles is promising. These technologies can be fully or partially renewable and thus last a long time. They reduce harm to the environment by lowering greenhouse-gas emissions, and they have the potential to close the chemical cycle and leave no change.

How to store it

Electrifying transportation breaks the exclusive dependence of transportation on oil, thereby enabling flexibility in fuelling as more sustainable alternatives for electricity generation become available. Electric motors are also far more efficient (over 90%) and mechanically much simpler than gasoline engines, and so are able to transport people and goods at a much lower cost per mile. The challenge is onboard storage or generation of electricity to power the electric motor. For batteries, the energy density must be increased by a factor of two to five from current levels before the journey range of electric vehicles becomes competitive with multipurpose gasoline vehicles (see “How to store it”). The materials challenges are to develop electrodes for higher energy density and longer life-cycles; non-aqueous electrolytes for higher operating voltages; and entirely new electrochemistry approaches such as lithium–air electrodes or doubly ionized cations that can lower the battery’s charge-to-mass ratio.

Fuel cells offer an alternative to batteries by generating electricity onboard via hydrogen oxidation. Developing this alternative requires scientific breakthroughs in catalysis for the oxygen-reduction reaction at fuel-cell cathodes, high-density storage of hydrogen in lightweight solid compounds and the production of hydrogen from renewable resources. Substantial progress has been made in the last five years towards overcoming these barriers to using hydrogen as an energy carrier, as indicated by the rise in the number of researchers and published papers in the field. Such advances raise the probability that fuel cells will be a viable long-term option for transportation.

The sustainability profile of electric transportation is potentially high because electricity, once produced, is environmentally benign and leaves no chemical change. The primary sustainability issue is the large-scale production of electricity for battery-powered vehicles or of hydrogen for fuel-cell vehicles. Existing production routes use fossil fuels to generate electricity and the reformation of natural gas to produce hydrogen; both deplete finite natural resources and emit substantial amounts of carbon dioxide. In contrast, using renewable electricity produced by solar and wind to charge batteries or solar-powered water splitting to produce hydrogen has the potential to last a long time, do no harm and leave no change. Achieving these renewable production routes will require breakthroughs in discovery and use-inspired basic science.

Pick and mix

So which of these more sustainable energy alternatives should we develop? The expected doubling of global energy demand by 2050 is too daunting a challenge to be met by any single technology – we are likely to need many or even all of them. Some of the most sustainable options require significant scientific breakthroughs before they can be implemented. We can, however, follow a dual course of phasing in portions of sustainable technologies as breakthroughs make them cost-competitive, while aggressively pursuing the research needed to meet the remaining challenges and achieve even greater sustainability. In this framework, carbon sequestration, high-efficiency nuclear electricity and plug-in hybrid vehicles are near-term solutions that will precede the deployment of large-scale solar and wind power generation, utility-scale electricity storage and all-electric vehicles.

A new leaf

The scientific advances needed for these more sustainable energy technologies reflect a fundamental sea change in the role of materials in energy technologies. With traditional fossil energy, the important materials are the fuels, which are valued for their high energy content and low cost. Burning fuels to produce heat is the first step in the traditional energy-use chain. This heat is then converted by an internal combustion engine to mechanical motion for transportation or by a turbine and generator to electricity for a diversity of energy services.

Sustainable energy technologies, in contrast, tap into underused energy flows like sunlight or wind and use these to produce electricity or fuel directly, without a combustion step. The important components are the hi-tech materials and chemical processes that initiate and control the conversion of energy between photons, electrons and chemical bonds via nano-scale phenomena. Unlike the fuels of fossil-energy technology, which are valued as a raw commodity, the hi-tech materials of sustainable energy are valued for their ability to coordinate sophisticated nano-scale energy-conversion processes.

Many decades of advances in observing and modelling phenomena at ever smaller length scales and shorter timescales mean that science is poised to enter a new era where researchers will not only observe, but also control these nano-scale conversion processes. This new capability promises powerful breakthroughs in raising the efficiency and lowering the cost of sustainable energy technologies.

Breaking the scientific bottleneck

Despite 30 years of research and development, the deployment of sustainable energy technologies has hardly affected the global energy mix. The world is still over 80% dependent on fossil fuels, much as it was in 1970. The reason is remarkably simple: the cost of alternative energies is significantly higher than fossil fuels, and the energy enterprise, driven by economics, will always choose the lowest available cost. This simple fact clearly identifies the basic deployment challenge for sustainable energy: we must make fundamental scientific breakthroughs in materials and chemical processes, and exploit them to make sustainable energies cheaper than fossil fuels.

That we have not succeeded in doing so in three decades indicates the magnitude of the challenge. Existing sustainable technologies do not control materials and chemistry at the sophisticated level needed to cost-effectively convert sustainable sources into useful energy. But unlike fossil energy, which after a century of development operates near its theoretical maximum efficiency, sustainable energy technologies are still in their infancy. There is generous room for improvement in raising efficiency and lowering cost before intrinsic limits are reached; we are, in effect, where we were with the steam engine in James Watt’s day. Multijunction solar cells, for example, where two or more semiconductors tuned to different band-gap energies are connected in series, have a theoretical efficiency of over 50%, well above the 22% of the best single-junction silicon solar cells now in commercial production.

Indeed, silicon solar cells themselves symbolize the im_pact of materials breakthroughs on sustainable energy technologies. Their efficiency has risen from 6% in the 1950s to 22% today because of dramatic improvements in control of the purity, perfection and precision doping of silicon. Similar big improvements in efficiency and cost await other sustainable-energy technologies – provided we aggressively pursue scientific research to control the materials and chemical processes that govern nano-scale energy conversion. Discovering and designing these hi-tech materials and processes is the grand challenge of sustainable energy.

From observation to control

A remarkable string of advances over the last half-century has allowed us to probe and understand energy-conversion phenomena at ever smaller lengths and shorter timescales. Aberration-corrected transmission electron microscopy, a wealth of scanning probe microscopies, laser- and accelerator-based ultrafast photon pulses, intense neutron beams and massively parallel teraflop computing are all helping us to unravel the structures and dynamics of the macromolecules, proteins and complex materials architectures that carry out energy conversion on the nano-scale.

Promising materials

The next step is to not only observe, but also control these fundamental energy-conversion phenomena. To do this, researchers need to exploit the remarkable progress that has been made in nanoscience, numerical modelling and complex materials. Nanoscience has given us techniques for nearly atom-by-atom construction of complex atomic and molecular architectures, including “top-down” techniques such as optical and electron beam lithography and “bottom-up” approaches like molecular beam epitaxy, ink-jet printing and the rich potential of directed self-assembly – as exemplified by DNA-driven biological construction. These fabrication tools give us the means to make nano-scale structures with the complexity, precision and functionality of computer chips, which we now routinely manufacture on the micro-scale.

Nanotubes offer versatile and promising opportunities for controlling energy conversion at the nano-scale. TiO₂ nanotubes like those pictured above are inexpensive, chemically inert, photostable, provide high surface-to-volume ratio and have band gaps that support sustainable energy technologies like solar water splitting, dye-sensitized solar cells and transparent conducting electrodes. They can be prepared by a variety of electrochemical processes, doped to tune their band gaps and decorated to promote surface catalytic activity.

On the modelling side, the past decade has seen computational speeds increase from teraflops (10¹² operations per second) to petaflops, with exaflops on the horizon. These remarkable hardware advances allow the simulation of million-atom assemblies and the detailed nano-scale energy conversions they perform. The potential of this large-scale atomistic simulation is not just incrementally better, but game-changing.

With these tools in hand, our challenge is to design materials and molecular assemblies that can convert energy among photons, electrons and chemical bonds with minimum losses. One guiding example is nature. Green plants manufacture their internal nano-scale architectures from abundant, environmentally friendly elements and recycle them harmlessly to the environment at the end of their useful life. They split water and carbon dioxide at room temperature using sunlight and use the liberated carbon and hydrogen to synthesize sugar to fuel their growth and reproduction. Plants emit unwanted oxygen to the atmosphere, where it is recycled to carbon dioxide by respiration in animals and other living things, closing the chemical cycle and leaving no change. Cellulose in the leaves and stalks of plants is rich in sugars that can be converted to ethanol and other biofuels, provided we can break down the protective coating of lignin that shields cellulose from physical and chemical attack during its life. We can learn from biology by observing how lignin breaks down on the forest floor and how sunlight splits water and carbon dioxide in the growing plant, and adapt these processes to create and control our own sustainable hydrocarbon fuel cycle.

Another emerging guide is numerical materials simulation, which allows us to imagine complex nano-scale structures and then simulate their behaviour to see if they function as we intend. Such simulations dramatically shorten nature’s design process, which proceeds by incremental random mutations of existing structures. Once filtered and refined by computer simulation, the most promising nano-scale energy-processing structures can then provide inspiration for fabrication.

Complexity is an essential ingredient in any functional design. Like information processing, energy processing requires many sequential steps, including manipulating quanta of energy in photonic, electronic and molecular excitations, as well as chemical transformation. Not only must each step in the sequence be understood and controlled, but also the individual steps must be integrated into a seamlessly functioning assembly that efficiently links the functions of its constituent parts. Information technology and biology provide two shining examples of the value and impact of complexity on functionality. We have mastered the micro-scale complexity of information technology; the next frontier is the nano-scale complexity of biological function and sustainable energy technology.

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

More about: Sustainability

V S Arunachalam et al. 2008 Harnessing materials for energy (special issue) MRS Bulletin 33 261–477
Basic Energy Sciences Advisory Committee 2007 Directing Matter and Energy: Five Challenges for Science and the Imagination; 2008 New Science for a Secure and Sustainable Energy Future www.sc.doe.gov/bes/reports/list.html
J Baxter et al. 2009 Nanoscale design to enable the revolution in renewable energy Energy and Environmental Sci. 2 559
M Eikerling et al. 2007 Driving the hydrogen economy Physics World July pp32–36
D Hafemeister et al. (ed) 2008 Physics of Sustainable Energy (Berkeley, 2008) (AIP Conf. Proc. 1044) (Melville, AIP)
Science 2007 Energy and sustainability (special issue) Science 315 737–815

Challenges in tackling climate change

When it comes to climate change, the gap between the vision of both scientists and engineers and the will of politicians is sometimes very stark. The problems caused by the changing climate are now better understood than ever, yet there is a frustrating sense of inertia when it comes to taking action.

The Fourth Assessment Report from the Intergovernmental Panel on Climate Change (IPCC) suggests that we must halve global greenhouse-gas emissions by 2050 in order to stand a good chance of limiting global warming from pre-industrial times to 2 °C. The UK’s independent Committee on Climate Change has recommended an 80% domestic reduction in the same period – a target now enshrined in the pioneering Climate Change Act passed in 2008.

Meeting these challenging targets will require nothing less than a revolution in the three areas of the UK’s energy mix: electricity, transport and heating. There are no silver bullets when it comes to low-carbon energy and governments should refrain from picking winners at this stage.

Energy barriers

So what might the future energy mix look like? In power generation, the UK could deploy a whole suite of renewable technologies currently at different stages of development: from mature technologies such as onshore wind plants and biomass energy plants to emerging technologies such as offshore wind facilities and photovoltaic solar cells to experimental technologies in wave and tidal power.

Integrating large amounts of renewable energy while also keeping costs down will require the development of a more flexible, “smarter” grid network that is able to intelligently manage consumer demand by communicating with meters installed in our homes. Energy from nuclear plants and fossil-fuel plants fitted with carbon capture and storage facilities could then provide clean, low-cost base-load generation from secure sources of nuclear fuel and indigenous coal.

In transport – which is currently 95% reliant on oil – first-generation biofuels from food crops are already in use, while second-generation “ligno-cellulosic” biofuels from energy crops are nearing the commercial development stage. Even in aviation, a sector that attracts its fair share of criticism, tests have shown that biofuels can be blended with kerosene in jet-engine fuel. There is also growing momentum behind electric cars, run on either renewable electricity or hydrogen fuel cells.

In heating, which is often forgotten in debates on energy policy, the UK could learn from other countries’ experiments with combined heat and power co-generation plants and district heating networks – using waste heat from small- and mid-scale power plants productively, close to where it is generated. Ground-source heat pumps that make use of natural geothermal energy might also prove to be a viable alternative to natural-gas boilers.

With so many technologies to choose from, it is clear that the greatest barriers to the low-carbon revolution are not scientific or technological. Nor, indeed, are they related to macroeconomic cost – various independent analyses put the figure at just a few percentage points of gross domestic product lost over the coming decades. The biggest barriers are in fact political.

Combating climate change

I would suggest four imperatives for politicians constructing energy policy in response to climate change. The first is not to compartmentalize climate change as an issue. Its effects will be extensive – affecting everything from weather patterns to defence policy – and our response to it must be equally broad. Politicians must lead from the front, demonstrating to their citizens that environmental integrity is a tangible part of other social priorities such as economic prosperity and national security.

Of course, there will be trade-offs between climate change and other social priorities. A potent example is the question of whether to build new coal-fired power plants, which would enhance energy security but at the expense of “locking in” harmful emissions for decades to come. We should not be uncharitable – decisions such as these represent a political dilemma of the highest order and there are few easy answers.

For this reason, the second imperative is to pursue action in areas of activity in which economic prosperity, national security and environmental integrity come together. Using public money for green-energy infrastructure and for energy-efficiency improvements would not only help reduce greenhouse-gas emissions, but also guide the path towards economic recovery and energy security.

There are some who argue that it is not the role of government to stimulate investment in new energy industries. But governments have been doing this for decades and with great success. The UK offshore oil and gas industry was created from virtually nothing during the 1970s and 1980s due, in part, to generous tax incentives and government help to build strategic infrastructure. There is an even greater cause for government intervention today because climate-change mitigation is a public good that would not otherwise be recognised by the free market.

Given this need for greater government intervention, the third imperative is for politicians to rethink the state’s role in energy markets. The market is the most effective delivery system available to society, but it needs strategic direction and a framework of rules if it is to provide the more diversified energy infrastructure that we urgently need.

And in troubled economic times, it is important that the government has a hand in directing financial resources to projects where they are urgently needed. In April the UK’s Chancellor of the Exchequer, Alistair Darling, announced £525m of support for offshore wind facilities that has been immediately successful in unlocking projects worth a combined 3000 MW.

The fourth, and final, imperative is that politicians must seek a global solution to climate change. The immediate battle against climate change will be mostly waged in the developing world. In the next decade, opportunities to reduce emissions in developing countries represent two-thirds of the global potential. What is more, this could be achieved at half the cost of action in the developed world.

What these four imperatives point to is a new direction for government policy in response to climate change. In previous years energy policy has been judged by two metrics: security and cost. To this we must now add a third: low-carbon generation.

The impact of this will affect every sector of the UK economy – from agriculture to finance, and from software management to civil engineering. It may feel a lot like stepping into the unknown but humanity has thrived in those moments where it has most pushed itself. For this generation, the task remains to bridge the gap between the scientifically possible and the politically feasible.

What the politicians say

Climate change cannot be tackled by politicians on their own but through politicians and people working together Ed Miliband, Secretary of State for Energy and Climate Change
No other major European country generates less of its electricity from renewables [than the UK], although we have some of the best wind, wave and tidal resources in Europe Greg Clark, Shadow Secretary of State for Energy and Climate Change
Developing our renewables as quickly as possible must be the highest energy priority Simon Hughes, Liberal Democrat Shadow Secretary of State for Energy and Climate Change

Web life: Clim’City

So what is the site about?

Like the popular SimCity computer-game series that inspired its name, Clim’City puts players in charge of a virtual city and allows them to choose how it develops. To win, players must reduce greenhouse-gas emissions by 75%, slash energy consumption by 40%, boost the share of renewable energy by 60%, and help citizens and businesses adapt to changing climate conditions – all within 50 years. The game offers a number of different ways to do this (developing wind power, insulating buildings, improving public transport, etc), but it is up to the individual player to decide which changes to implement, and in what order.

Who is behind the site?

It was launched in early 2009 by the Cap Sciences museum in Bordeaux, France. The full site is still only available in French, but the game itself has been translated (imperfectly but adequately) into English.

What is it like to play?

The main screen of Clim’City shows a model city with mountainous outskirts, a populous coastline and various structures in between. Clicking on these structures brings up menus of possible actions, along with information about their consequences. For example, at the city’s power station, you can choose to burn cleaner fuel oil or natural gas instead of coal, or to research (and then implement) carbon capture and storage. Some actions are contingent on others: you can also make the power station run on wood, but only if you have already developed the city’s biomass production facility. Each action consumes political, enterprise or citizen “points”, which represent the cost of getting different parts of the city to adopt your plans. When you run out of points, time moves forward by a year. A series of graphs lets you see your city’s chances of meeting its goals.

This is harder than it looks. Any tips?

The game provides numerical information about how long each action will take to implement, and how much energy consumption and/or emissions will fall as a result. Paying attention to these quantities – rather than simply picking actions that sound nice – will improve your final score. In addition, graphs showing how much energy/ pollution each sector of the economy is using/ producing can help players identify which areas require more action. It is also worth noting that a few actions, like reinforcing sea defences, do not reduce emissions or energy use. However, they can prevent players from losing valuable points if, say, a massive storm strikes the city later in the game.

Who is it aimed at?

With its cartoon interface and easily mastered gameplay, Clim’City looks like a kids’ game. Indeed, the French-language site contains a wealth of educational graphs, maps and interviews that are not yet available in translation; science teachers on good terms with their school’s French department might find some opportunities here for jointly taught lessons. But be warned: this game is far easier to play than it is to win, and adults as well as children will struggle to meet the demanding (some might say impossible) targets for victory.

How realistic is it?

Very – almost to the point of being discouraging. Consider the following. If you do nothing, both emissions and energy use will tick inexorably upwards, in line with current trends. Some of the most effective actions – like closing the city tip or producing hydrogen at the solar power station – are really expensive, and require action on multiple fronts. It is far easier to run out of “enterprise points” than any other type, so even when you have plenty of political will and an enthusiastic citizenry, there is still only so much change that industries can absorb each year. In fact, the game’s only unrealistic aspect may be the relative ease of meeting its target for “adaptation”; if the current furore over energy-saving light bulbs is any indication, people are far less willing to change their habits than this game assumes. Still, as a simple (and addictive) demonstration of the difficult energy choices facing the world, Clim’City is hard to beat – in more ways than one.

Fisheye gives new route to perfect images

A fisheye lens proposed over a century ago can produce perfectly focused images without using any exotic “negative refractive index” materials, a physicist in the UK has calculated.

Ulf Leonhardt of St Andrews University claims that a fisheye lens – of the type invented by the great 19th century physicist and mathematician James Clerk Maxwell – can focus beyond the troublesome diffraction limit, which precludes standard lenses from achieving a resolution finer than the wavelength of light.

Scientists thought perfect lenses were unattainable until 2000, when physicist John Pendry of Imperial College London showed that materials with a negative index of refraction – that is, those that bend light the “wrong” way – should beat the diffraction limit. But engineering such materials proved difficult, and it was only in 2005 that two groups in the US created the first “superlens” which could image features with a size just one-sixth the wavelength of light.

‘Unlimited resolution’

Now Leonhardt has shown that Maxwell’s idea, first published over 150 years ago, can give perfect images without negative refraction. “It is the waviness of light that limits the resolution of lenses,” said Leonhardt in a press statement. “Apparently, nobody had tried to calculate the imaging of light waves in Maxwell’s fisheye. The new research proves that the fisheye has unlimited resolution in principle, and, as it does not need negative refraction, it may also work in practice.”

Maxwell’s fisheye involved a refractive index profile that matches the geometry of a sphere. With this profile, light rays emitting from any direction on one point of the sphere would follow circles all the way round until they meet, perfectly, on the opposite side. Put a plane at the equator, however, and these rays would instead be mapped onto the plane’s two dimensions – rather like cartographers map the globe onto a flat sheet of paper. Again, this mapped image would in principle have perfect resolution.

Could this be done in practice? The problem, as Leonhardt points out, is that distortion inherent in the mapping would require light on one side of the sphere to travel faster than the speed of light in the vacuum – a known impossibility. A way around this, he says, would be to place a mirror around the sphere’s equator so that the rays give the illusion of travelling all the way round, when in fact they are reflected and are therefore travelling at subluminal speeds.

Slab of silica

Leonhardt describes how a researcher could make a flat, two-dimensional version of the lens. In would consist of a slab of silica with tiny air holes or silicon pillars to create the refractive index profile, with a circular mirror placed on top. Unlike a superlens, in which negative refraction tends to have the unwanted side effects of high absorption and a narrow wavelength-range of operation, the fisheye lens would have high light transmission and would work across a broad part of the electromagnetic spectrum.

There could be many applications of the fisheye lens. For example, if a researcher were to place a sliver of material with an unusual structure against the lens and shine a light through it, the sliver would act as a mask, and the lens could focus an image of the structure onto a light-sensitive surface such as a photoresist. This would enable a new breed of electronics with features at atomic resolution.

‘Work in progress’

Leonhardt told physicsworld.com that a group at Cornell University in the US is attempting to realize his design, although it is “work in progress for the time being.”

The research is published in the New Journal of Physics.

Nobel predictions

Albert Fert: who will be the next winner?

By Hamish Johnston

Earlier this week I was at a Royal Society meeting on spintronics to film the latest in our series of interviews with high-profile physicists.

My first interviewee was the Nobel laureate Albert Fert, who shared the 2007 prize for his work on giant magnetoresistance. I asked Prof Fert for his predictions for this year’s prize — which will be awarded next Tuesday — and he tipped his Orsay colleague Alain Aspect.

In 1981, Aspect and colleagues were the first to demonstrate quantum entanglement at a distance — as defined by the violation of Bell’s inequality. Since then physicists including David Wineland, Peter Zoller, Juan Ignacio Cirac and Anton Zeilinger have invented ways of using entanglement as the basis of quantum cryptography and nascent quantum processors.

Indeed, Zoller and Cirac have been tipped by Thomson Reuters for the prize.

So how about Aspect plus two of Zoller, Cirac, Zeilinger or Wineland for this year’s award? But how to choose — and is it too early for a quantum-information prize, which will surely be given some day?

Another suggestion that came up in London is a prize for the 1995 discovery of the first planet orbiting a star other than the Sun. A long shot — but it would have exoplanet pioneers Michel Mayor and Didier Queloz packing their DJs for Stockholm.

What do folks around here think?

James Dacey predicts quantum cryptography — and Anton Zeilinger in particular.

Michael Banks says “Saul Perlmutter and Brian Schmidt for discovering that the expansion of the universe is accelerating. Outside bet is Andre Geim and Konstantin Novoselov for the discovery of graphene.”

“Yakir Aharanov for the Aharanov-Bohm effect and Michael Berry for the Berry phase,” says Physics World supremo Matin Durrani. “If I keep saying it often enough, it surely will happen. This year marks the 50th anniversary of the AB effect and 25 years since Berry’s paper so the timing is appropriate.”

So, what do you think?

New printing method takes a cue from nature

By mimicking the ‘structural colours’ found in butterfly wings and peacock feathers, researchers in South Korea and the US have developed a high-resolution patterning technique that produces multiple colours within seconds. If the technique is scaled up for commercial use, it could be used to prevent forgery and lead to the design of advanced materials, say the scientists.

“We have developed a simple, scalable way of producing structural colour,” explained Sunghoon Kwon, Seoul National University (SNU), who heads up the research. “We have overcome limitations in previous approaches to demonstrate rapid production of high-resolution patterns of multiple structural colours.”

Structural colours, such as those on butterfly wings and peacock feathers, differ from traditional pigments or dyes in that the colour results from the interaction of light with periodic structures on the surface of the material.

Cannot be mimicked or bleached

Among the advantages of structural colour are that it cannot be mimicked by chemical pigments or dyes and it is immune to photobleaching. What is more, multiple colours can be displayed using a single material simply by varying the dimension of the periodic nanostructures.

Colour field

Such properties make structural colour printing attractive for a range of applications, including forgery protection and the design of new materials. To date, however, attempts to manufacture artificial structural colour have proved time-consuming. This is because they involve either the precise assembly of colloids of different sizes or the stacking and lithographic patterning of periodic dielectric materials.

Now, Kwon and colleagues at Seoul National University, working in collaboration with chemists at the University of California at Riverside, have found a way to produce a single ink of any desired colour within a few seconds. The material, dubbed “M-Ink”, changes colour when a magnetic field is applied. What is more, the colour can be rapidly locked into the material by shining patterned ultraviolet light onto its surface.

Aligning along magnetic field lines

“Under an external magnetic field, the CNCs are assembled to form chain-like periodic structures” Yadong Yin, UC Riverside

“M-Ink is a three-phase material system consisting of superparamagnetic colloidal nanocrystal clusters (CNCs), a solvation liquid and a photocurable resin,” explained UC Riverside’s Yadong Yin, an expert in nanomaterials chemistry. “Under an external magnetic field, the CNCs are assembled to form chain-like periodic structures, which align themselves along the magnetic field lines.”

In a similar way as periodic structures in conventional photonic crystal diffract light at specific wavelengths, so too do the particles that make up the CNCs. A shorter interparticle distance corresponds to a shorter diffracted wavelength. Because the this distance is determined by the applied magnetic field, the colour of the material can be altered simply by varying the magnetic field strength.

Frozen in the polymer network

Once the desired colour is obtained from M-Ink, it can be fixed by solidifying the photocurable resin through ultraviolet exposure. The chain-like CNCs are then effectively frozen in the polymer network.

“We can freeze the self-assembled photonic nanostructure fast enough to prevent distortion” Sunghoon Kwon, Seoul National University

“As our photocuring is instantaneous, we can freeze the self-assembled photonic nanostructure fast enough to prevent distortion,” commented Kwon. “This means that we retain the structural colour.”

The group hopes to commercialize the material in conjunction with companies in the electronics or material design industries.

The work is described in Nature Photonics.

Sociology of the Galaxy Zoo

Stampede Galaxy Zoo has recruited 200 000 citizen scientists in its two year history

By James Dacey

Since its launch in 2007, the project known as Galaxy Zoo can only really be described as a roaring success. Its basic premise is that any “citizen scientist” with an internet connection can help professional scientists by classifying images of galaxies from the Sloan Digital Sky Survey.

As of April 2009, more than 200,000 volunteers had made more than 100 million galaxy classifications.

In practice the would-be “Zooites” are asked to follow a quick tutorial which describes the basic structures of spirals, ellipticals etc, before they are tested with some extra pictures. Get enough correct answers and they can join.

So what is it that attracts non-specialists to pass their spare time by sitting at a computer and classifying galaxies? This is a question explored by a group of public outreach specialists from the UK and the US, in a new paper on the arXiv preprint server.

22 Zooites volunteered themselves for an interview in which they were asked a series of questions including their impressions of the Galaxy Zoo website, their motivations for participating, and their experiences with and definition of science.

Following a series of analysis and discussions, the research team arrived at 12 motivational categories:

Contribute
Learning
Discovery
Community
Teaching
Beauty
Fun
Vastness
Helping
Zoo
Astronomy
Science

For elaboration on each category, check out the paper — it’s very “social-sciency”, but well worth a look if you’re into this kind of thing.

For more info on the purpose of the Galaxy Zoo, check out this feature written by two of the project’s founders.