How will the geosciences contribute to achieving a sustainable energy supply in the 21st Century and beyond?
The geosciences have a crucial role to play in achieving a sustainable energy supply in this century and beyond. Current energy supply is far from sustainable with the vast majority of energy globally supplied by non-renewable fossil fuels, which not only are finite in supply, but their combustion releases vast amounts of carbon dioxide and other pollutants into the atmosphere causing global warming, air, soil and water pollution and damage to many ecosystems. Over the next century, ongoing growth and development, particularly in the developing world, will greatly increase the global demand for energy, and has the potential to destroy much of our environment if present practices do not change to more sustainable ones. Sustainable in this sense is defined as “capable of being maintained at a steady level without exhausting natural resources or causing severe ecological damage” (Collins English Dictionary, 2001). Transformation to a sustainable energy supply will require firstly making the use of non-renewable fossil fuels and nuclear energy less unsustainable, secondly, developing and expanding energy supplies from renewable sources and thirdly reducing levels of consumption, particularly in the affluent consumerist societies. The geosciences have a major contribution to make to the first two of these and a lesser contribution to the third. I shall consider each in turn, taking a global perspective.
Making non-renewable energy less unsustainable
While the use of any non-renewable resource is by definition not sustainable, in that a finite resource will eventually be depleted, its use can be made significantly less ecologically damaging than is presently the case. Currently some three-quarters of global energy is supplied by the fossil fuels: coal, oil and natural gas, and nuclear power makes a small but growing contribution. While many developed countries are now actively moving towards more renewable energy sources, non-renewable fuels will certainly continue to play a major role in the developed, and more importantly the developing, world for the foreseeable future. Ultimately a sustainable energy supply will not include non-renewable resources, but such a strategy is not realistic at the present time. However, it is realistic to make the use of these energy sources considerably less unsustainable than it presently is. This requires maximising the efficiency of systems using non-renewable resources and minimising the detrimental environmental effects at all stages, from mining, through processing and burning, to dealing with the by-products, particularly carbon dioxide and nuclear waste. I shall reflect on how the geosciences can contribute to achieving this for each fuel.
Coal resources are abundant and more equitably distributed around the globe than oil or gas. Importantly for the developing nations, they are found in considerable quantity in China and India. At current production rates, today’s reserves will last some 200 years (Church, p70) and the relative cheapness and ease of extraction and use mean that coal will inevitably continue to play an important role in energy supply on a global basis for many years to come. Geoscientific knowledge is important in ensuring that mining and its after-effects do not cause long-term damage to the environment and also that the products of combustion are dealt with safely. Coal mining can be very destructive to the environment during and for a long time after coal extraction, particularly due to acid discharge causing water pollution. Knowledge of ground structure and aquifers can suggest approaches that will minimise such problems and allow restoration of mined areas in an environmentally positive manner. But while mining creates local and downstream problems, the release of atmospheric pollutants during combustion of coal can cause much more widespread problems, regionally and globally. These atmospheric pollutants include carbon dioxide and, depending on the grade of the coal, varying quantities of particulate matter, sulphur and nitrogen oxides. Local air quality is diminished by soot and gases. Sulphur, and to a lesser extent nitrogen gases cause acidic atmospheric depositions on a regional scale, killing plant and animal life and destroying forests, particularly in areas where the soil is already naturally acidic. While the aim must be to prevent this pollution in the first place, knowledge of soil and water chemistry can provide strategies to minimise and reverse the negative effects that have already occurred. Most important of the gaseous pollutants is carbon dioxide, a greenhouse gas, whose rapid accumulation in the atmosphere is contributing to climate change on a global scale. Current technology can significantly reduce the amount of particulate matter, sulphur and nitrogen emitted during combustion, although this technology is not yet in use in many areas, but carbon dioxide is more difficult to control.
Oil and gas, which together make up around half of current global energy supply, also contribute strongly to the anthropogenic rise in atmospheric carbon dioxide levels. Oil and gas resources are more concentrated in their distribution than coal, with roughly 60% of oil reserves and 40% of gas reserves being found in the Middle East (Whiteley, p110,112), and so as well as the environmental concerns there is an additional political dimension providing impetus for a move away from a dependence on this energy source. In many areas outside the Middle East, production of oil and gas has already peaked and is now in decline. Most of the large, easily-accessible resources have already been exploited, and although large resources still exist, they are more dispersed, such as Canada’s oil sands, requiring greater inputs of energy and capital to extract the resource. Production from such sources carries greater potential for negative environmental impact than conventional sources. Ensuring that such production is as minimally destructive as possible will require detailed geological knowledge of the area for managing the extraction, decommissioning and restoration phases to militate against these impacts.
As with coal, oil and gas produce carbon dioxide on combustion. But whereas coal is mostly used in electricity generation at power stations so emissions are localised, oil is also widely used in transport, particularly road and air, so the carbon dioxide is additionally generated from millions of smaller sources which are therefore more difficult to control. Technology is developing to trap carbon dioxide from the emissions at power stations, but the prospects of widespread trapping of vehicular carbon dioxide are still remote and it may transpire that an alternative carbon-free transportation fuel is more practical than trapping the carbon dioxide produced by using oil. Once trapped, carbon dioxide must be sequestered so that it will remain out of contact with the atmosphere for several centuries at the least. The search for potential sites for sequestration falls within the remit of the geoscientist. Current strategies include the use of depleted oil and gas wells, which has the added advantage that during the latter stages of extraction carbon dioxide injection can enhance recovery of the remaining oil. Other possible sites may include the deep ocean floor in gas hydrate form, but further research and monitoring are required to establish the safety and long-term effectiveness of such strategies. Carbon capturing from power stations and its subsequent sequestration has the potential to significantly decrease carbon dioxide emissions, reducing the rate of rise of atmospheric carbon dioxide levels, but at present this remains an expensive strategy. However, as increasing coal use seems inevitable over the next few decades especially in the developing world, widespread introduction of these technologies would go a long way towards making coal use less unsustainable.
A further sequestration strategy involves increasing carbon sinks. The atmospheric carbon dioxide level has not risen by as much as would be expected if all the carbon dioxide emitted over the last century or so had accumulated there, so natural carbon sinks such as vegetation and the oceans must be absorbing some of the excess. Geoscientific study can lead to a greater understanding of how these sinks work and the potential they may offer to limit the rise in atmospheric carbon dioxide levels. Increasing the forest cover removes carbon dioxide from the atmosphere, but research can reveal which locations and types of forest would do so most effectively and how other objectives such as maintaining biodiversity could be met at the same time. Attempts to increase the ocean’s absorption of atmospheric carbon dioxide, for example by seeding with iron, have not generally shown long-term success, and indeed there are suggestions that the limit on the ocean’s capacity to absorb carbon dioxide is close to being reached.
The other major non-renewable source of energy is uranium used in nuclear power. Uranium is a finite resource, its mining frequently involves considerable environmental damage, both at the time and subsequently, and a safe means of disposal for the radioactive by-products of its use has yet to be found. However its great advantage over the fossil fuels is the absence of carbon dioxide emissions from nuclear power generation, although the energy used to extract and transport uranium and build the power plants is not so carbon-neutral. Nuclear power is rather out of favour in many developed countries at present for several reasons including the public perception of the risks of a major Chernobyl-style catastrophe, the difficulty in finding disposal options for radioactive material and concerns over fissile material falling into the hands of terrorists. But globally there is still a lot of interest in nuclear power. The majority of new reactors currently under construction are being built in Asia and it would appear that nuclear power generation is set to increase over coming decades. So as with the fossil fuels, nuclear power can never be a truly sustainable source of energy, but it can be made less unsustainable than it currently is. The simple fact that it will continue be an important component of global energy supply means that attention should be focussed in this direction. One example is the ongoing search for alternative forms of nuclear fuel, such as thorium and recycled fuel, which are more terrorist-proof and decrease the requirement for primary uranium. It is important that reactors be sited in geologically stable areas to avoid the risk of a natural disaster causing a nuclear catastrophe.
As with coal mining, geological knowledge can contribute to making the extraction of uranium less detrimental to the local environment. The problem unique to nuclear energy is the radioactive nature of the waste products, both mine and mill tailing and spent fuel. Although nuclear power plants use relatively small volumes of fuel compared with fossil fuel plants, as most uranium ore deposits contain less than 1% uranium, large volumes of tailings are produced. These contain not only uranium and other radioactive isotopes, but often also high concentrations of toxic heavy metals and sulphur which are frequently present in the source rock. Radioactive windblown dust and carcinogenic radon gas are the main radiation hazards of the tailings. Extracting uranium by in situ leaching avoids the problems with solid waste but instead generates liquid sludge waste, and poses a risk of groundwater contamination. Safe disposal of tailings requires burial in lined pits which will remain intact, out of contact with groundwater for hundreds of years (Abdelouas, 2006).
Spent reactor fuel poses a much more serious radiation hazard. The radioactivity of spent fuel is many orders of magnitude greater than that of the original fuel, containing a vast array of radioactive isotopes, many with very long half-lives. While there is a significant reduction in radioactivity after several hundred years, it will be several hundreds of thousands of years before the radioactivity of the spent fuel approaches that of the original ore (Bruno & Ewing, 2006). Finding a safe, ultra-long-term means of disposal for such material is the major geological and technical challenge of today, and generates much controversy. The basic principle is to contain the vitrified waste in thick casings and bury it deep underground in geological repositories. The waste will generate a lot of heat, so the containment must be resistant to heat and radioactivity. It must also be resistant to water over extremely long periods of time. A further crucial feature is that the repository be in a geological stable area, that will be safe for many millennia from earthquakes and faulting which may breach the containment field. A number of potential sites for repositories have been explored but none is yet in use, mainly due to the opposition aroused by those concerned about long-term effects, which cannot be fully modelled in short-term laboratory experiments. Nevertheless, the prospect of the increasing use of nuclear power as an energy source, which will generate large quantities of spent fuel, makes it imperative that a solution be found in the not-too-distant future.
Expanding renewable sources
Currently only a small percentage of global energy is provided by renewable resources, although in a few regions where geological conditions are favourable, renewable sources such as hydroelectric and geothermal energy make a large contribution. The geosciences provide an understanding of potential sources of renewable energy, and so have an important role to play in the expansion of these energy sources which must eventually take over from fossil fuels and nuclear energy to achieve a sustainable energy supply. While some renewable sources have already been explored and developed to a considerable extent, others are in very early stages of development. It is important to be aware however that “renewable” does not necessarily equate with sustainable or environmentally-friendly. Some projects to harness renewable energy may cause considerable environmental harm or be completely inefficient, so the focus must be kept on the sustainable development of renewable resources.
As with non-renewable sources, renewable energy sources are not evenly distributed around the globe. For example, mountainous countries may possess considerable hydroelectric potential, while volcanic regions are favoured with geothermal power and countries at low latitude profit from abundant solar energy. Nevertheless most sources can be exploited to at least some degree almost everywhere, and small-scale local and domestic projects to harness such low-intensity energy for local requirements may form an important component of future energy strategies. One disadvantage of many renewable sources is their inconstancy or unpredictability. Solar energy, for example, can only be harnessed during daylight hours, tidal flows are cyclic and wind is highly variable. Increasing utilisation of these forms of energy will therefore require energy storage mechanisms and integrated management of energy sources so that a constant supply may be maintained while inputs from different sources vary. Of the renewable energy sources, solar and wind power have the greatest potential to meet energy demands on a global scale. I will discuss some of the renewable sources in turn.
Wind energy is currently expanding rapidly in Europe with ever-larger land and sea-based wind farms using ever-larger turbines springing up in many places. Knowledge of wind patterns enables the selection of locations and positioning of turbines in a way that maximises the wind power they can harness. But optimal access to the winds is not the only consideration. Large wind farms occupy large areas of land or sea. Large volumes of concrete are used at the base of each turbine, and access roads between turbines or cabling on the seabed take more land or seabed out of the ecosystem. A large network of turbines at sea will affect water flow patterns and may disrupt sedimentological processes and animal movement routes, particularly for larger species. Turbines may also present a hazard to birds. So an appreciation of more than local average wind speeds is necessary to ensure that wind farms generate sustainable energy. As current wind farm developments have an expected lifespan of around 30 years, there is a need to make provision for decommissioning of wind farms at the end of their life in a manner that protects the environment.
More novel approaches to harnessing wind energy from higher levels in the atmosphere are currently being examined. Wind speeds are greater and more constant higher in the atmosphere, so a more reliable energy supply could be achieved if a means to harness this wind power could be developed. A number of such ideas are presently under consideration including a flying generator to harness the jet stream at an altitude of 10 km (The Economist, 7/06/07). While any such projects are far from realisation, if technology can be developed to harness high-level wind power, it could greatly increase the potential of wind energy and reduce the adverse effects of large wind farms on land and sea.
Water already makes a significant contribution to global energy, with hydroelectricity providing almost one sixth of global electricity, mostly from large-scale damming projects. However these large dams can have major negative environmental impacts which are increasingly being recognised and need to be addressed to ensure that water provides sustainable energy. On construction, dams submerge large areas of land upstream which may include valuable agricultural land and homes. The reservoirs trap and eventually become filled with sediment which contain toxins such as heavy metals. The interruption of flow to downstream areas has major impacts on water supply and sedimentation patterns and river life is disturbed, with interruption of migration pathways and often introduced species flourish at the expense of native species. All these aspects need to be considered and mitigated when a dam is constructed. Of course, dams can also bring benefits such as flood control and provision of water supply. Widespread awareness of the potential negative impacts of dams, as well as the massive capital investment required, is making it more difficult to build large hydroelectric plants nowadays, as the opposition to the proposed damming of the lower Mekong river illustrates.
In the developed countries, large dams are generally going out of favour, and there is now an emphasis on finding environmentally-safe ways to decommission dams, which involves dealing with the toxins accumulated in the reservoirs and restoring animal and plant life to something approaching its native form once the dam is dismantled. But hydroelectric power need not involve large dams across major rivers. There is considerable potential for smaller-scale electricity generation from small plants located within the river’s normal flow, or from partial diversions of the river. These smaller-scale projects avoid much of the negative environmental impact of large dams and reservoirs and can be widely used in smaller rivers with much less capital outlay.
The above projects make use of the gravitational energy of flowing water, but the thermal energy of water can also be exploited. Water from the ocean has been used to generate electricity, although not on any large scale. The temperature difference between deep and shallow water provides the energy source, but current plants have very low efficiency rates because of the energy required to pump the water. While this is unlikely to ever provide a significant amount of energy, it may have some potential as a sustainable energy source for local purposes on small islands or coastal areas with little negative impact on the environment.
The temperature profile of water has also been employed in cooling systems, not as an energy source but to run air-conditioning units and so reduce energy demand. In Toronto, deep water from Lake Ontario at 4ºC is used to cool a number of buildings in the city centre (The Economist, 7/06/07).
Geothermal energy provides a major potential renewable energy source in parts of the world where there is active volcanic activity and high heat flow in the earth’s crust, and so makes a significant contribution to energy supply in places such as New Zealand. But there is also much potential for deriving energy from geothermal sources in regions where the heat flow is not as obvious. Active igneous intrusions provide a heat source in the crust which can be exploited by tapping nearby aquifers for heated groundwater, as for example in Tuscany in Italy. Older granitic intrusions which have high concentrations of naturally occurring radioactive isotopes also provide a heat source, though a less accessible one as they are not generally permeable to water. Harnessing energy from such sources requires artificially fracturing the rock to provide pathways for injected water to be heated before retrieval. This is a highly complex and technical procedure and it is unlikely that this will yield significant amounts of energy in the future.
Low-grade geothermal energy can also be exploited, almost anywhere, by using an underground heat exchange system to extract the energy of normal heat flow for space heating and cooling. This can be used on a variety of scales, from individual houses to larger industrial or civic installations. Generally speaking, the utilisation of geothermal energy has little negative environmental impact and although its ability to provide significant contributions to the energy supply is limited to certain geographical locations, on a smaller scale it could be widely used to provide winter heating and summer cooling, so reducing overall energy demands.
Solar energy has considerable potential as an energy source particularly in the developing world, most of which is located at low latitudes that receive high insolation, although current high costs of the technology limit its application. Direct solar heating is used on a range of scales, from cooking and domestic heating of space and water, to large-scale plants, concentrating solar energy with mirrors that heat water to generate electricity. Photovoltaic cells also generate electricity on both small and large scales. These can utilise not only direct sunlight, but diffuse daylight, so can play an important role in higher latitude regions. One problem of solar technology is the large area needed over which to collect sunlight. Placing panels on buildings makes good use of external walls and roofs and has little negative environmental impact. On the other hand, schemes whereby panels cover large areas of land, blocking out all sunlight to the ground will have an adverse effect on the ecosystems present there. Large-scale installations of panels in deserts may harness a lot of energy, but far from where it is required, so an environmentally-friendly means of transporting the energy would be needed. As the technology becomes more affordable, it is to be expected that solar energy will greatly increase its contribution to global energy supply over coming decades.
Tidal and wave energy have the potential to make a small contribution to a sustainable energy supply. Neither of these energy sources is widely used yet, although a tidal power plant has been in operation in France for over 40 years, but new technological developments may provide the means to increase their role. However both can cause environmental disruption which needs to be considered in any scheme. Tidal barrages pose similar environmental problems to the dams used for hydroelectricity generation, affecting sedimentation patterns and animal and bird life. There are only a limited number of sites around the world where tidal ranges are large enough to generate a significant amount of electricity, but there is also potential for small-scale energy harnessing using floating turbines, without barrages and therefore without significant environmental impact. Wave power can be harnessed either at coastal sites or off-shore, but is most consistent in inhospitable parts of the ocean far from land, limiting its usefulness.
Biomass is another potential source of renewable energy. It covers a range of resources, from traditional wood burning to more innovative applications for a variety of waste materials, which can be used for electricity generation or, as it is portable, unlike other renewable resources, as a fuel for transportation. Recovering the energy content from waste has the advantage of reducing waste going into landfill sites, and while biomass combustion releases carbon dioxide, it is carbon from the active carbon cycle, already cycling between the atmosphere and vegetation reservoirs, as opposed to fossil fuels which add “new” carbon dioxide, taken from long-term storage in the rocks, to the atmosphere. However, if the carbon can be trapped and sequestered, as with fossil fuel-derived carbon, biomass combustion could serve as a carbon sink, contributing to lowering atmospheric carbon dioxide levels. Yet the use of biomass as an energy source, as with the other renewable sources, is not necessarily sustainable or environmentally-friendly. The use of specially-grown crops, as opposed to waste, for biofuel takes valuable agricultural land out of food production, and may encourage the clearing of forests for land, and intensive fertiliser use that damages ecosystems. Often the overall process requires more energy than it eventually yields. If technology is developed to efficiently convert cellulose to biofuel, so the waste part of regular crops and forestry waste are used rather than specially-grown crops, this problem could be overcome.
So there are a wide range of renewable sources known to the geoscientist that can be exploited to supply sustainable energy. However each has its problems and can be used to the detriment of the environment, especially in large-scale projects, if care is not taken to prevent this. Many of the sources are unpredictable or intermittent, requiring a means of storage or an integrated system to provide back-up supply from another source. Only biomass is portable, imparting the freedom to use it when and where it is required and making it an option for transportation fuel. A possible form of storage in the future may be hydrogen, which could be generated by any of the above means, and used at a remote time and place, giving it also potential as a transportation fuel. However many of these renewable sources are in their early days, and further development is required before they can enter widespread service around the globe, producing energy efficiently and cost-effectively without harming the environment.
Reducing consumption
Reducing consumption requires increasing the efficiency of energy use, at all levels in society and decreasing the demand for energy by making lifestyle changes at the level of the individual. Increasing efficiency is mainly a technical matter, extracting more useable energy from the source and doing more work with that amount of energy. Decreasing demand by making lifestyle changes requires an individual commitment to the cause of sustainability. Such a commitment develops in response to the perception that a problem exists and personal action involving some sacrifice of convenience is an effective remedy to the problem. The geosciences furnish us with an understanding of our Earth system and the crises it is now facing, and an appreciation for the value of the environment, both for itself, and as our life-support system. Disseminating this information to the public, as well as those in charge of policy development, will raise awareness of current environmental problems and the need to transform our society into a sustainable society to safeguard our means of survival. It is to be hoped that such information will lead to the personal commitments and lifestyle changes that are required to achieve a reduction from the present excessive levels of consumption in most of the developed world.
Conclusion
A sustainable energy supply in the 21st century and beyond will require the continuing research and development of new technologies as well as policy development at the national and international level to support sustainable energy, but underlying the technology and policies there must be a firm geoscientific foundation. Moving to a sustainable energy supply requires a three-pronged approach, making non-renewable energy use less unsustainable, increasing renewable energy use and decreasing consumption. The geosciences will contribute to this process firstly by enabling extraction of fossil fuels and uranium to be minimally destructive to the environment and sound restoration to be achieved after extraction, and by finding solutions to the problems of carbon sequestration and the disposal of nuclear waste. Secondly, they will contribute to the development and expansion of sustainable renewable energy use, through discovering novel energy sources and ensuring that their exploitation is not to the detriment of the environment. Thirdly, the geosciences have a role in promoting an understanding of the finite capacity of our planet to sustain humanity and therefore the need to decrease energy consumption both by increasing the efficiency of energy production and use, and by altering the high-consumption patterns of behaviour in most developed countries. The geosciences alone cannot provide a sustainable energy supply but they have a major role to play in informing those who develop technology, formulate policy and consumers in general, so that all can play their part in achieving the goal of having sufficient energy resources to live a good and comfortable life without impairing the ability of our children and their children to do the same.