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What energy levels can the Earth sustain?
ARTICLE IN PRESS Energy Policy 37 (2009) 2469–2474
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What energy levels can the Earth sustain? Patrick Moriarty a,, Damon Honnery b a b
Department of Industrial Design, Monash University, P.O. Box 197, Caulfield East 3145, Vic., Australia Department of Mechanical and Aerospace Engineering, Monash University, P.O. Box 31, 3800 Vic., Australia
a r t i c l e in fo
abstract
Article history: Received 12 February 2009 Accepted 3 March 2009 Available online 2 April 2009
Several official reports on future global primary energy production and use develop scenarios which suggest that the high energy growth rates of the 20th century will continue unabated until 2050 and even beyond. In this paper we examine whether any combination of fossil, nuclear, and renewable energy sources can deliver such levels of primary energy—around 1000 EJ in 2050. We find that too much emphasis has been placed on whether or not reserves in the case of fossil and nuclear energy, or technical potential in the case of renewable energy, can support the levels of energy use forecast. In contrast, our analysis stresses the crucial importance of the interaction of technical potentials for annual production with environmental factors, social, political, and economic concerns and limited time frames for implementation, in heavily constraining the real energy options for the future. Together, these constraints suggest that future energy consumption will be significantly lower than the present level. & 2009 Elsevier Ltd. All rights reserved.
Keywords: Forecasting Fossil fuels Climate change
1. Introduction Modern industrial economies depend critically on energy, although conventional economists have been slow to recognise its importance. Continued economic growth would seem to require further increases in energy use, or ‘useful work’ (Ayres, 2008a, b). Increases are also needed to overcome declining soil fertility (fertiliser manufacture), declining fresh water availability (irrigation, desalination) and declining availability of high-quality reserves of both mineral ores and fossil energy. Much higher global energy use would also be necessary if industrialising economies are even to approach the per capita levels of OECD countries (Moriarty and Honnery, 2008). For these reasons, most official projections of global primary energy use over the 21st century assume that it will be greater – usually much greater – than the present value of roughly 500 EJ (EJ ¼ exajoule ¼ 1018 J) (International Energy Agency (IEA), 2008a). Following IEA conventions, in this paper energy generated from renewable primary electricity sources such as hydroelectricity or wind is converted to primary energy on a one-to-one basis, and primary energy includes non-commercial fuel wood. Table 1 gives the range of values for global primary energy use in the various scenarios developed in recent reports by the IEA (2008a), the US Energy Information Administration (EIA, 2008), the World Energy Council (WEC) (Schiffer, 2008), the European Commission (EC, 2006) and the International Atomic Energy
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Agency (IAEA, 2008). What is remarkable is the small variation in energy use for a given future year, both between the various scenarios in any one study, and also between the different studies; even in 2050 the maximum range is only 26%. Presently, fossil fuels have an 81% share of primary energy, renewable energy (RE) 13% and nuclear energy 6% (IEA, 2008a). The various studies agree that out to 2050 at least, fossil carbon energy sources will remain dominant, with roughly an 80% share of total primary energy. Clearly, these official sources believe that future availability of fossil fuels will not be a problem. Primary rather than secondary energy is the main focus of this paper, not only because most official projections are given in such energy terms, but also because the environmental impacts of energy use vary more closely with primary energy. It is also the relevant value to consider when discussing fossil fuel depletion. Total primary energy supply is made up of global production7 stock changes. Secondary energy (or total final consumption as IEA terms it) is the sum of consumption by the different end-use sectors (excluding backflows from the petrochemical industry). In 1973 the ratio of secondary energy to primary energy was 0.76, but this ratio had fallen to 0.69 by 2006 (IEA, 2008a), mainly because of the rising share of electricity in global final energy demand. The EC study (EC, 2006) projects that the ratio will further fall to 0.66 in 2030, and 0.61 in 2050, as electricity further increases its share. In this paper we likewise assume that the projected figures in Table 1 imply total final consumption of 66% in 2030 and 61% in 2050 of these primary energy values. The main aim of this paper is to determine whether or not high levels of primary energy are likely to be available to us in the decades to come. We analyse future prospects for fossil fuels, RE
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Table 1 Global primary energy consumption projections, 2020–2100 (EJ). Organisation/Source
2020
2030
2050
EIA (2008) IAEA (2008) IEA (2008a) EC (2006) WEC (Schiffer 2008)
609–677 588–655 NA 571–608 616–674
666–807 679–826 661–742 649–706 701–847
NA NA NA 821–933 846–1151
and nuclear energy in turn, and find that too much emphasis has been placed on the availability of adequate reserves (or technical potential in the case of renewable energy) in assessing the likely levels of energy use in the future. In contrast, our analysis stresses the crucial importance of the interaction of technical potentials for annual production with environmental factors, social, political, and economic concerns, and limited time frames for implementation, in heavily constraining the real energy options for the future. Together, these constraints suggest that energy consumption will be significantly lower than the present level.
2. Hydrocarbon fossil fuels World consumption of fossil fuels in 2007 totalled 409.0 EJ, comprising 165.5 EJ for oil, 133.0 EJ for coal, and 110.5 EJ for natural gas (BP, 2008). Future fossil fuel use faces two uncertainties: first, the extent of recoverable reserves, both proven and yetto-find, and, second, how much of these finite reserves to use each year. Discussions about proven recoverable oil reserves and annual production rates need a consistent terminology. Here we follow the definitions of the Association for the Study of Peak Oil (ASPO) and include as non-conventional oil not only heavy oils (e.g. oil sands and shale oils) but also polar and deep-water oil, and natural gas liquids. This wider definition seems reasonable, since deep-water oil is reported to need a price of $US 70/barrel and oil sands $US 90/barrel to ensure a reasonable rate of return on investment (ASPO, 2009). By this definition, global production of conventional oil may already have peaked several years ago. Indeed, ASPO consider that production of all oil peaked in 2007, and that production of both oil and gas combined (both conventional and non-conventional) will peak around 2010 (ASPO, 2009). Most official organisations would agree with ASPO that the era of cheap oil is over—or will only occur under global economic recession conditions, when demand is weak. But even if it is acknowledged that conventional oil might be nearing (or even having reached) peak production, official organisations are far more optimistic on non-conventional oil. Thus the IEA (2008b) state: ‘The total long-term potentially recoverable oil-resource base, including extra-heavy oil, oil sands and oil shales (another largely undeveloped, though costly resource), is estimated at around 6.5 trillion barrels.’ [about 40,000 EJ]. Similarly, natural gas has very large non-conventional sources (coal seam methane, ‘tight’ gas, and even methane hydrates). For coal, estimated reserves of lower calorific value ‘sub-bituminous coal and lignite’ exceed those for ‘anthracite and bituminous coal’. Although combined reserves are only 18,000 EJ (BP, 2008), the ultimately recoverable reserves are usually thought to be many times higher (e.g. Sims et al., 2007). Other researchers (Energy Watch Group, 2007; Nel and Cooper, 2009) argue that ultimately recoverable coal reserves have been greatly exaggerated. If these lower reserve estimates, and those for oil and gas by ASPO are true, then combined fossil fuel production will peak in a couple of decades
(Moriarty and Honnery, 2009). In any case, the monetary, energy and environmental costs of unconventional fossil fuel extraction are all likely to be high. Adequate global reserves of fossil fuels are a necessary but by no means sufficient condition for ensuring rising production in the coming decades. The IEA (2008b) stress that lack of investment in new production capacity, particularly given the collapse of oil prices toward the end of 2008, could lead to lowerthan-expected future oil output. Globally, before the recent demand slump, spare capacity was at a very low level, and large increases in new capacity are needed, not only to allow for added growth in world output foreseen by the IEA, but more importantly, to replace capacity losses as mature oil fields decline. The IEA now recognise that existing field output is declining much faster than expected (IEA, 2008b). Much of the production development will need to be for non-conventional oil supplies, with their heavy demands for capital. Capacity increases will also be needed in other parts of the oil supply chain, including tankers, pipelines, and refining capacity. Export reductions will occur if the domestic consumption of OPEC countries continues its rapid rise of recent years (BP, 2008). Reductions could also occur through export restrictions by fuel exporters, as such countries can and do restrict exports for political and economic reasons. OPEC has recently cut output in an attempt to support oil prices, but in the past has also restricted oil exports for political reasons. Similarly, Russia has occasionally restricted natural gas exports to other European countries. Fear of these restrictions has prompted interest in ‘energy security’ in importing countries. Oil is the only resource for a number of oil exporting nations. Restricting production now can both maintain oil prices while also leaving more for future production and exports. A further reason for export constraint is that petroleum in future may be far more valuable as a feedstock for plastics than as a fuel. Future restrictions could even occur with gas and coal exports. Production constraints could also be in the long-term interests of wealthy importing countries, given that it would enable a steady stream of imports for centuries. Finally, future global production of fossil fuels could fall well below present levels simply because of a drop in demand, as in the present (2009) economic downturn. Several researchers (Hall and Klitgaard, 2006; Ayres, 2008a,b) have examined the strong correlation between GDP and primary energy consumption, the correlation becoming even tighter when corrections for changing energy quality are made. If this strong link continues to hold, large reductions in primary energy use will lead to corresponding reductions in GDP. The various environmental impacts of fossil fuel production and combustion form another set of factors that could limit the annual supply of fossil fuels. Greenhouse gas atmospheric emissions from the heavy use of fossil fuels projected in Table 1 would need to be drastically reduced by sequestering the CO2. Yet carbon capture from existing power plants is expensive and energy intensive, thus reducing the delivered energy for a given input of primary energy (Moriarty and Honnery, 2009). For the projected values of secondary energy assumed above, use of carbon capture (especially air capture) and storage will only hasten depletion of fossil fuel reserves, because primary energy needs would then be much higher than given in Table 1. Even without carbon sequestration, maintaining the assumed secondary to primary energy ratios will be impossible if the shares of non-conventional oil and gas, and lower calorific value coal rise, or if coal-to-oil plants are built. Also, much of the coal in place consists of deeply buried seams, or thin seams. In both cases, the overburden per tonne of coal produced will be high (and with it the monetary and environmental costs), if strip mining, the cheapest option, is used.
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In summary, fossil fuel production and use in future could be constrained by geological depletion of economically recoverable fuels, economic or politically imposed limits to annual production from energy-exporting nations, and environmentally imposed limits on fossil fuel use. There is, of course, a potential solution to possible future supply shortfalls of fossil fuels: many argue (see e.g. Momirlan and Veziroglu, 2005; de Vries et al., 2007; Sims et al., 2007; Matsui et al., 2008; Forsberg, 2009) that renewable or nuclear energy (or both together) can more than compensate for any shortfalls. By this logic, it would then be in the interests of fossil fuel exporters to produce as fast as possible, to avoid being left with an unsaleable product. In the next two sections we argue that alternatives to fossil fuels are insufficient to allow us to continue on the energy path forecast in Table 1.
3. Renewable energy In 2006, total production of modern forms of RE was around 17.0 EJ, with the largest being hydropower (11.1 EJ) and modern biomass (4.6 EJ). Most RE was from fuel wood in developing countries, estimated to be about 45 EJ. The average annual growth rate for modern RE was around 2.5% from 1980 to 2000, but since then has risen to about 3% (BP, 2008). If we assume that this 3% growth rate continues out to 2030, modern RE would then total 33 EJ, roughly twice its 2006 value. Higher growth rates are unlikely because of expected slower growth in hydro and modern biomass, which account for nearly 95% of the total. In a 2007 IEA assessment, the scenario most favourable for RE also assumed an approximate doubling in modern RE by 2030. In contrast, global use of fuel wood was expected to decrease in the coming decades, displaced by modern energy sources (IEA, 2007). Estimating future RE potential is more than usually complicated for several reasons. First, it often depends on technology which is not yet commercially proven. Although hydropower, biomass combustion and conventional geothermal power are mature technologies, their technical potential is limited (Pimentel et al., 2002; Moriarty and Honnery, 2007a,b, 2009). On the other hand, the RE source with by far the largest potential, direct solar, awaits fundamental technology breakthroughs for unit costs to be reduced to anywhere near existing levels. A very rough calculation illustrates the scale of the cost problem. A US report estimated that the global solar electricity market in 2005 was in excess of $US 10 billion/year (Lewis, 2007). In 2005, solar electrical energy output was 0.01 EJ. Supplying all the roughly 500 EJ of primary used globally each year with solar energy would thus cost $US 500 trillion, an order of magnitude larger than the 2006 world gross national income (World Bank, 2008). These costs in turn suggest that total input energy costs are much higher than usually calculated, resulting in little or no net energy. Already, the current economic downturn is adversely affecting PV cell sales (Sanderson, 2009). Like solar, large scale use of wind also presents challenges, although wind turbine technology is by now well developed. Current global wind energy production is less than one EJ, far below our estimated global technical potential of 229 EJ. Realizing this potential would require construction of over 24 million 2 MW turbines, roughly 500 times as many 2 MW units as are currently needed. Further, large scale use of wind and solar will require energy storage and conversion, again with further technical challenges—and added costs. Converting electricity to hydrogen which could be stored, typically results in a 45% loss (Honnery and Moriarty, 2009). Second, possible limits to RE technical potential could arise from the finite nature of some of the material inputs necessary for a given RE. This is particularly the case for solar PV cells, where
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several options are foreclosed because of the limited global reserves of needed metals (Feltrin and Freundlich, 2008). Third, ongoing climate and other environmental changes – including land-use changes – will likely adversely affect future RE technical potential and especially individual project viability, as detailed for hydro and biomass in our previous papers (Moriarty and Honnery, 2007a,b, 2009). The various forms of RE are very sensitive to adverse environmental impacts, since their assumed environmental advantages are an important reason for preferring them over fossil fuels. Not only could ongoing environmental and land-use changes reduce overall RE technical potential, but all RE sources themselves can have potentially serious environmental impacts when deployed on a large scale (see, e.g. Abbasi and Abbasi, 2000; Pimentel et al., 2002; Trainer, 2007; Babir, 2008; Cowern and Ahn, 2008; Makarieva et al., 2008; Schroder, 2008). The natural world freely provides humans – and all other living organisms – with a variety of ecosystem services, which are vital for our and their continued existence. For humans, the obvious ones are the provisioning services of food, fibre, lumber and fresh water. These in turn depend on a variety of other less-obvious regulating ecosystem services, including pest control, plant pollination and air and water quality (Millennium Ecosystems Assessment, 2005; Carpenter et al., 2009). Widely deployed, RE can act to undermine ecosystem services. Equally important, the various provisioning ecosystem services can be in conflict with each other. Particularly in the case of biomass, the expansion of renewable energy can compromise the provision of food, forestry and other fibre products, as an analysis of terrestrial net primary production (NPP) shows. NPP is a measure of the net conversion of atmospheric CO2 by photosynthesis into plant biomass (mainly natural vegetation) over a given time period, and is obtained by subtracting the autotrophic (self) respiration of plants from gross biomass production. Photosynthesis on land produces an annual total NPP of roughly 120 billion tonnes dry matter, or 1900 EJ (Moriarty and Honnery, 2007a; Field et al., 2008). Kleidon (2006) has argued that attempts to increase the global human appropriation of NPP (HANPP) much above his presentday estimate of 40% are self-defeating. His simulated results, using ‘a coupled dynamic vegetation–climate system model of intermediate complexity’ show that as the HANPP fraction grows, the absolute value of HANPP (in terms of gC/m2/day, for example) will begin to fall after reaching about 45%. In other words, since output of food, forestry and other fibre products will need to be expanded (because of ever-rising human numbers) in a world where ongoing climate changes could adversely affect output, the potential for sustainable bioenergy production could be close to zero. Likewise, Field et al. (2008) estimate that only 27 EJ of biomass energy can be harvested globally without undermining food production or worsening climate change. Further, cellulosic biomass may never be a feedstock for liquid fuels; a recent paper (Felix and Tilley, 2008) found that conversion of switchgrass to ethanol may not yield net energy. Already, global species extinction is estimated at around 12,000 per year, or 0.25% per year of all Earth’s species (Avise et al., 2008). Any expansion of HANPP will accelerate this species loss. Although biomass and hydro have the most adverse effects on the environment and its continued ability to deliver ecological services, all RE sources can be expected to have some negative effects. The negative effects of biomass and hydro may in part simply result from their already-widespread deployment, and the required 3–4 orders of magnitude scale-up of wind and solar energy could well reveal similar problems. As an example, although much has been made of bird kills by wind turbines, bat kills are far more frequent. It appears that migratory tree-roosting
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species are most at risk, but why they are killed in such numbers is uncertain (Kunz et al., 2007). These insect-eating bats help provide an important ecosystem service—pest control. Just as important as environmental effects, RE can also endanger human life. Kerr and Stone (2009) report recent research which argues that the filling of the Zipingpu hydro dam may have been responsible for the devastating 2008 Sichuan earthquake. The filling of the Koyna Reservoir in India, was judged responsible for a 1967 earthquake which killed 200 people. Although citizens’ opposition to various forms of RE installations often focuses on environmental issues to press their case, it can also result from more personal concerns. Less-pressing, perhaps, are worries that local construction of wind farms might lower real estate prices or spoil the view. But, particularly with hydro schemes in the developing countries, opposition is often motivated by well-founded fears of losing one’s home, livelihood and way of life. Such opposition arises partly because of the large land requirements for most forms of RE compared with the other two energy sources (Pimentel et al., 2002). Future use of RE is thus highly uncertain, for a variety of reasons. The optimistic technical potentials (often many thousand EJ) reported in the literature (e.g. Momirlan and Veziroglu, 2005; de Vries et al., 2007) not only depend on unprecedented technological advances, but also assume that no environmental changes adverse to RE production occur. Further, RE sources, like other energy sources, can in turn have serious environmental consequences, potentially undermining both their political support and the environmental services the natural world provides.
4. Nuclear energy At the end of 2007, some 439 nuclear power plants were in operation around the world, with a total generating capacity of 372 gigawatt (GW) supplying 9.4 EJ of electric power in 2007 (IAEA, 2008). Global proven reserves of uranium are 2.85 million tonne (MT); ultimately recoverable conventional resources are estimated at 17.1 MT. If, in the extreme case, present-day thermal reactor types had to provide 1000 EJ annually, even 17.1 MT would only last for about 10 years and 2.85 MT for less than two years (Moriarty and Honnery, 2007a). On the other hand, at present rates of annual nuclear power output, 17.1 MT would last the world for several hundred years. The IAEA (2008), in assessing the future of nuclear energy, projected that in the low-growth case, nuclear energy’s share of global electricity generation in 2030 would fall from its 2007 value of 14.2% to 12.4%. Even in their high-growth scenario, nuclear’s share would only increase to 14.4%, just above its present level. The EIA (2008) high- and low-growth projections are very similar to those of the IAEA. Both sets of forecasts were made before the current global economic downturn, and more recently one nuclear consultant predicted that ‘the industry will not even be able to replace the units being shut down because of ageing’ (Brumfiel, 2008a). The prospects for rapid growth in nuclear power are not helped by escalating construction costs; in the US the cost of planned 1 GW nuclear plants is as high as $US 10 billion (Romm, 2008). Given this low anticipated output of nuclear energy, fuel constraints are unlikely to restrict output. However, the low growth of nuclear power in recent decades, particularly in Western Europe and North America, is not only a consequence of high costs. Political opposition has led a number of countries to veto nuclear power plants, and others, such as Germany, to commit to phasing out existing programs. Other parts of the fuel cycle may also face opposition; the state of Nevada in the
US opposes construction of a nuclear waste repository at Yucca Mountain. Although opposition to nuclear power is usually labelled environmentalist, nuclear operations, with the important exception of uranium mining, have few direct effects on earth’s energy and material flows, or ecosystems. Negligible greenhouse gas emissions are released during reactor operation, although they are incurred in other parts of the fuel cycle, especially in reactor construction and uranium enrichment. Instead, opposition has been based largely on the health and safety risks to humans. These can arise from human error, as in the Chernobyl reactor accident, from deliberate human actions, such as the diversion of fissile materials for nuclear weapons, or from natural hazards. Although fires, floods and even tsunamis could conceivably affect reactor safety, earthquakes are the main hazard. In 2007, the world’s largest nuclear power complex at Kashiwazaki-Kariwa in Japan, was struck by a 6.6 magnitude earthquake. The seven reactors were undamaged, but the fault line was previously unknown to the plants’ designers. The reactors have not yet been restarted (Sacchetti, 2008). Up to 2030, only thermal reactors, chiefly modified versions of existing light water reactors, are expected to be in operation. Beyond 2030, breeder reactors are a possibility. Breeder reactors could in principle extend uranium reserves by a factor of 30, but face severe technical problems given their high operating temperatures, and significantly increased risk of nuclear proliferation (Moriarty and Honnery, 2007a, 2009). The breeding rate of new fissile material (and costs and difficulties of fuel reprocessing) could be the limiting factor on the rate of expansion. Further, like all fission reactor types, they contain a large inventory of highly radioactive materials, which could conceivably be released by a reactor accident or sabotage. Their risks to human health and safety would overall be much greater than for thermal reactors. Research on fusion energy has been in progress for half a century, but fusion is still nowhere near commercial realisation, which, if it ever occurs, will not be before the last quarter of this century. The favoured approach is confining deuterium–tritium plasma in a toroidal magnetic field. While this approach may be superior from a physics viewpoint, the engineering problems are daunting, mainly because of the intense neutron flux and its effect on the blanket-shield and the reactor structural materials (Parkins, 2006). Electricity costs will be higher, possibly many times higher, than for existing fission-based electricity (Hirsch, 2003). With its rising capital costs and lack of private investor interest, nuclear power of any type will be struggling to maintain its existing output levels.
5. Policy implications Most energy analysts think that global primary energy use in the decades to come will be much higher than present levels, with projections for the year 2050 often 1000 EJ or more. Even the IEA (2008b) projections, which take into account the current global economic downturn, foresee 2030 primary energy of 712 EJ in the base case. Yet the energy sources that singly or together must meet this projected demand – fossil fuels, RE, and nuclear power – all face three categories of possible limitations, namely:
Physical limits such as geological limits on fossil fuel reserves. Political, economic, technical or social constraints on their production.
Environmental constraints on their production or use. These categories are not independent of each other, but can interact. Fears of impending fossil fuel reserve depletion could
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encourage either energy-exporting or -importing countries to limit production/use below that possible at that time. Similarly, environmental problems from energy production or use (especially CO2 emissions from fossil fuels) could hasten moves by citizen groups or policy-makers to limit its use. Advocates for high future energy use often acknowledge that much of this energy will need to come from technologies not yet commercial, and sometimes not even at the demonstration stage. They can point to the remarkable technical advances over the past century as reasons for optimism, but such optimism about new energy sources may be misplaced, for several reasons. First, in contrast to advances in information technology, experience shows that new energy sources are usually more costly than anticipated, and take much longer to gain a significant market share. Second, new technologies will increasingly be subjected to constraints on their use: for instance, they may require materials in scarce supply, their large-scale deployment may uncover novel environmental problems, or ongoing changes in global land-use and climate may reduce their potential for use. Our analysis so far suggests that even holding primary, and even more so delivered energy, at present levels in 2050 will prove difficult. Several implications for policy follow. First, we will need to avoid as far as possible the use of non-conventional fossil fuels, since these have higher than average primary/secondary energy ratios, and thus higher environmental damages, including CO2 emissions per unit of secondary energy. A second, related, point is the need to avoid carbon capture (especially air capture) and sequestration, as this will likewise increase the primary/ secondary energy ratio. Attempts to maintain, let alone raise, secondary energy output will thus also hasten fossil fuel depletion. We have argued elsewhere that restricting annual use of primary energy from fossil fuels to 50–100 EJ would both remove the need for carbon capture and storage and also permit use of fossil fuels for several centuries (Moriarty and Honnery, 2009). It would also reduce the need for large increases in nonconventional fossil fuel use. The third policy implication is that we should delay for as long as possible the need for conversion and storage of intermittent RE sources—mainly wind and solar energy. We have so far only discussed energy from a global viewpoint, but, of course, countries differ greatly in their energy resource endowments. If modern RE only doubles by 2030, as suggested above, and electricity use grows as forecast, grid integration of intermittent RE is unlikely to be a serious technical problem in any country. But given the limited potential of baseload RE, the cost and risk problems facing nuclear fission expansion, and the desirability – and perhaps need – to reduce fossil fuel use, the share of intermittent electricity in grids could grow rapidly. Also, if wind/ solar electricity expand more rapidly than anticipated, the need for conversion/storage will be brought forward; if this is not possible, electricity grid management practices will need to be changed. Without either of these two interventions, the nature of the existing electricity grid will ultimately limit intermittent RE production. The current use of fossil fuels brings about another problem. Since fossil fuels dominate our existing energy system, they will have to power any possible shift to RE or nuclear sources. The effect this has on fossil fuel reserves will depend largely on the size and speed of the shift, since fossil fuel energy used will be additional to that already in use. If changes to climate warrant a decisive shift to RE within the next decade, this shift would not only hasten depletion of fossil fuels, but could also hasten climate change. If the shift to RE was powered by RE alone, it is likely the rate of change would be too small; we would possibly see significant climate problems or face fossil fuel depletion before RE could supply large amounts of primary energy.
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Clearly, there are no easy choices facing future production and use of energy for most countries. Even if fossil fuel reserves are closer to the optimist position, there is no guarantee that political or environmental constraints, particularly the need for greenhouse gas emission reductions, will not greatly limit annual output. But if deep cuts are made to fossil fuel use, the resulting large spare capacity will slow change away from fossil fuel power plants. Only large reductions in global primary energy use, with all its difficulties of implementation, can meet the resource, environmental, economic and political problems that future energy use will face.
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Moriarty, P., Honnery, D., 2009. Hydrogen’s role in an uncertain energy future. International Journal of Hydrogen Energy 34, 31–39. Nel, W.P., Cooper, C.J., 2009. Implications of fossil fuel constraints on economic growth and global warming. Energy Policy 37, 166–180. Parkins, W.E., 2006. Fusion power: will it ever come? Science 311, 1380. Pimentel, D., Herz, M., Glickstein, M., Zimmerman, M., Allen, R., Becker, K., et al., 2002. Renewable energy: current and potential issues. BioScience 52, 1111–1120. Romm, J., 2008. The Self-Limiting Future of Nuclear Power. Accessed on 27/01/09 at /www.americanprogressaction.orgS. Sacchetti, D., 2008. Earth, wind and fire: preparing nuclear power plants for nature’s fury, IAEA Bulletin, 50–1, 50–53. Sanderson, K., 2009. Not so sunny after all. Nature 457, 362–363. Schiffer, H.-W., 2008. WEC energy policy scenarios to 2050. Energy Policy. Schroder, W.U., 2008. Energy realpolitik: towards a sustainable energy strategy. Accessed on 5/12/2008 at /http://arxiv.org/ftp/arxiv/papers/0804/0804.2159. pdfS. Sims, R.E.H., Schock, R.N., Adegbululgbe, A., Fenhann, J., Konstantinaviciute, I., Moomaw, W., et al., 2007. Energy supply. In: Metz, B., Davidson, O.R., Bosch, P.R., Dave, R., Meyer, L.A. (Eds.), Climate Change 2007: Mitigation. CUP, Cambridge, UK, pp. 251–322. Trainer, T., 2007. Renewable Energy Cannot Sustain a Consumer Society. Springer, Dordrecht, NL. World Bank, 2008. Key Development Data and Statistics. Accessed on 29/01/09 at /http://web.worldbank.orgS.
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Viewpoint
What energy levels can the Earth sustain? Patrick Moriarty a,, Damon Honnery b a b
Department of Industrial Design, Monash University, P.O. Box 197, Caulfield East 3145, Vic., Australia Department of Mechanical and Aerospace Engineering, Monash University, P.O. Box 31, 3800 Vic., Australia
a r t i c l e in fo
abstract
Article history: Received 12 February 2009 Accepted 3 March 2009 Available online 2 April 2009
Several official reports on future global primary energy production and use develop scenarios which suggest that the high energy growth rates of the 20th century will continue unabated until 2050 and even beyond. In this paper we examine whether any combination of fossil, nuclear, and renewable energy sources can deliver such levels of primary energy—around 1000 EJ in 2050. We find that too much emphasis has been placed on whether or not reserves in the case of fossil and nuclear energy, or technical potential in the case of renewable energy, can support the levels of energy use forecast. In contrast, our analysis stresses the crucial importance of the interaction of technical potentials for annual production with environmental factors, social, political, and economic concerns and limited time frames for implementation, in heavily constraining the real energy options for the future. Together, these constraints suggest that future energy consumption will be significantly lower than the present level. & 2009 Elsevier Ltd. All rights reserved.
Keywords: Forecasting Fossil fuels Climate change
1. Introduction Modern industrial economies depend critically on energy, although conventional economists have been slow to recognise its importance. Continued economic growth would seem to require further increases in energy use, or ‘useful work’ (Ayres, 2008a, b). Increases are also needed to overcome declining soil fertility (fertiliser manufacture), declining fresh water availability (irrigation, desalination) and declining availability of high-quality reserves of both mineral ores and fossil energy. Much higher global energy use would also be necessary if industrialising economies are even to approach the per capita levels of OECD countries (Moriarty and Honnery, 2008). For these reasons, most official projections of global primary energy use over the 21st century assume that it will be greater – usually much greater – than the present value of roughly 500 EJ (EJ ¼ exajoule ¼ 1018 J) (International Energy Agency (IEA), 2008a). Following IEA conventions, in this paper energy generated from renewable primary electricity sources such as hydroelectricity or wind is converted to primary energy on a one-to-one basis, and primary energy includes non-commercial fuel wood. Table 1 gives the range of values for global primary energy use in the various scenarios developed in recent reports by the IEA (2008a), the US Energy Information Administration (EIA, 2008), the World Energy Council (WEC) (Schiffer, 2008), the European Commission (EC, 2006) and the International Atomic Energy
Corresponding author. Tel.: +61 3 9903 2584; fax: +61 3 9903 1440.
E-mail address: [email protected] (P. Moriarty). 0301-4215/$ - see front matter & 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.enpol.2009.03.006
Agency (IAEA, 2008). What is remarkable is the small variation in energy use for a given future year, both between the various scenarios in any one study, and also between the different studies; even in 2050 the maximum range is only 26%. Presently, fossil fuels have an 81% share of primary energy, renewable energy (RE) 13% and nuclear energy 6% (IEA, 2008a). The various studies agree that out to 2050 at least, fossil carbon energy sources will remain dominant, with roughly an 80% share of total primary energy. Clearly, these official sources believe that future availability of fossil fuels will not be a problem. Primary rather than secondary energy is the main focus of this paper, not only because most official projections are given in such energy terms, but also because the environmental impacts of energy use vary more closely with primary energy. It is also the relevant value to consider when discussing fossil fuel depletion. Total primary energy supply is made up of global production7 stock changes. Secondary energy (or total final consumption as IEA terms it) is the sum of consumption by the different end-use sectors (excluding backflows from the petrochemical industry). In 1973 the ratio of secondary energy to primary energy was 0.76, but this ratio had fallen to 0.69 by 2006 (IEA, 2008a), mainly because of the rising share of electricity in global final energy demand. The EC study (EC, 2006) projects that the ratio will further fall to 0.66 in 2030, and 0.61 in 2050, as electricity further increases its share. In this paper we likewise assume that the projected figures in Table 1 imply total final consumption of 66% in 2030 and 61% in 2050 of these primary energy values. The main aim of this paper is to determine whether or not high levels of primary energy are likely to be available to us in the decades to come. We analyse future prospects for fossil fuels, RE
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Table 1 Global primary energy consumption projections, 2020–2100 (EJ). Organisation/Source
2020
2030
2050
EIA (2008) IAEA (2008) IEA (2008a) EC (2006) WEC (Schiffer 2008)
609–677 588–655 NA 571–608 616–674
666–807 679–826 661–742 649–706 701–847
NA NA NA 821–933 846–1151
and nuclear energy in turn, and find that too much emphasis has been placed on the availability of adequate reserves (or technical potential in the case of renewable energy) in assessing the likely levels of energy use in the future. In contrast, our analysis stresses the crucial importance of the interaction of technical potentials for annual production with environmental factors, social, political, and economic concerns, and limited time frames for implementation, in heavily constraining the real energy options for the future. Together, these constraints suggest that energy consumption will be significantly lower than the present level.
2. Hydrocarbon fossil fuels World consumption of fossil fuels in 2007 totalled 409.0 EJ, comprising 165.5 EJ for oil, 133.0 EJ for coal, and 110.5 EJ for natural gas (BP, 2008). Future fossil fuel use faces two uncertainties: first, the extent of recoverable reserves, both proven and yetto-find, and, second, how much of these finite reserves to use each year. Discussions about proven recoverable oil reserves and annual production rates need a consistent terminology. Here we follow the definitions of the Association for the Study of Peak Oil (ASPO) and include as non-conventional oil not only heavy oils (e.g. oil sands and shale oils) but also polar and deep-water oil, and natural gas liquids. This wider definition seems reasonable, since deep-water oil is reported to need a price of $US 70/barrel and oil sands $US 90/barrel to ensure a reasonable rate of return on investment (ASPO, 2009). By this definition, global production of conventional oil may already have peaked several years ago. Indeed, ASPO consider that production of all oil peaked in 2007, and that production of both oil and gas combined (both conventional and non-conventional) will peak around 2010 (ASPO, 2009). Most official organisations would agree with ASPO that the era of cheap oil is over—or will only occur under global economic recession conditions, when demand is weak. But even if it is acknowledged that conventional oil might be nearing (or even having reached) peak production, official organisations are far more optimistic on non-conventional oil. Thus the IEA (2008b) state: ‘The total long-term potentially recoverable oil-resource base, including extra-heavy oil, oil sands and oil shales (another largely undeveloped, though costly resource), is estimated at around 6.5 trillion barrels.’ [about 40,000 EJ]. Similarly, natural gas has very large non-conventional sources (coal seam methane, ‘tight’ gas, and even methane hydrates). For coal, estimated reserves of lower calorific value ‘sub-bituminous coal and lignite’ exceed those for ‘anthracite and bituminous coal’. Although combined reserves are only 18,000 EJ (BP, 2008), the ultimately recoverable reserves are usually thought to be many times higher (e.g. Sims et al., 2007). Other researchers (Energy Watch Group, 2007; Nel and Cooper, 2009) argue that ultimately recoverable coal reserves have been greatly exaggerated. If these lower reserve estimates, and those for oil and gas by ASPO are true, then combined fossil fuel production will peak in a couple of decades
(Moriarty and Honnery, 2009). In any case, the monetary, energy and environmental costs of unconventional fossil fuel extraction are all likely to be high. Adequate global reserves of fossil fuels are a necessary but by no means sufficient condition for ensuring rising production in the coming decades. The IEA (2008b) stress that lack of investment in new production capacity, particularly given the collapse of oil prices toward the end of 2008, could lead to lowerthan-expected future oil output. Globally, before the recent demand slump, spare capacity was at a very low level, and large increases in new capacity are needed, not only to allow for added growth in world output foreseen by the IEA, but more importantly, to replace capacity losses as mature oil fields decline. The IEA now recognise that existing field output is declining much faster than expected (IEA, 2008b). Much of the production development will need to be for non-conventional oil supplies, with their heavy demands for capital. Capacity increases will also be needed in other parts of the oil supply chain, including tankers, pipelines, and refining capacity. Export reductions will occur if the domestic consumption of OPEC countries continues its rapid rise of recent years (BP, 2008). Reductions could also occur through export restrictions by fuel exporters, as such countries can and do restrict exports for political and economic reasons. OPEC has recently cut output in an attempt to support oil prices, but in the past has also restricted oil exports for political reasons. Similarly, Russia has occasionally restricted natural gas exports to other European countries. Fear of these restrictions has prompted interest in ‘energy security’ in importing countries. Oil is the only resource for a number of oil exporting nations. Restricting production now can both maintain oil prices while also leaving more for future production and exports. A further reason for export constraint is that petroleum in future may be far more valuable as a feedstock for plastics than as a fuel. Future restrictions could even occur with gas and coal exports. Production constraints could also be in the long-term interests of wealthy importing countries, given that it would enable a steady stream of imports for centuries. Finally, future global production of fossil fuels could fall well below present levels simply because of a drop in demand, as in the present (2009) economic downturn. Several researchers (Hall and Klitgaard, 2006; Ayres, 2008a,b) have examined the strong correlation between GDP and primary energy consumption, the correlation becoming even tighter when corrections for changing energy quality are made. If this strong link continues to hold, large reductions in primary energy use will lead to corresponding reductions in GDP. The various environmental impacts of fossil fuel production and combustion form another set of factors that could limit the annual supply of fossil fuels. Greenhouse gas atmospheric emissions from the heavy use of fossil fuels projected in Table 1 would need to be drastically reduced by sequestering the CO2. Yet carbon capture from existing power plants is expensive and energy intensive, thus reducing the delivered energy for a given input of primary energy (Moriarty and Honnery, 2009). For the projected values of secondary energy assumed above, use of carbon capture (especially air capture) and storage will only hasten depletion of fossil fuel reserves, because primary energy needs would then be much higher than given in Table 1. Even without carbon sequestration, maintaining the assumed secondary to primary energy ratios will be impossible if the shares of non-conventional oil and gas, and lower calorific value coal rise, or if coal-to-oil plants are built. Also, much of the coal in place consists of deeply buried seams, or thin seams. In both cases, the overburden per tonne of coal produced will be high (and with it the monetary and environmental costs), if strip mining, the cheapest option, is used.
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In summary, fossil fuel production and use in future could be constrained by geological depletion of economically recoverable fuels, economic or politically imposed limits to annual production from energy-exporting nations, and environmentally imposed limits on fossil fuel use. There is, of course, a potential solution to possible future supply shortfalls of fossil fuels: many argue (see e.g. Momirlan and Veziroglu, 2005; de Vries et al., 2007; Sims et al., 2007; Matsui et al., 2008; Forsberg, 2009) that renewable or nuclear energy (or both together) can more than compensate for any shortfalls. By this logic, it would then be in the interests of fossil fuel exporters to produce as fast as possible, to avoid being left with an unsaleable product. In the next two sections we argue that alternatives to fossil fuels are insufficient to allow us to continue on the energy path forecast in Table 1.
3. Renewable energy In 2006, total production of modern forms of RE was around 17.0 EJ, with the largest being hydropower (11.1 EJ) and modern biomass (4.6 EJ). Most RE was from fuel wood in developing countries, estimated to be about 45 EJ. The average annual growth rate for modern RE was around 2.5% from 1980 to 2000, but since then has risen to about 3% (BP, 2008). If we assume that this 3% growth rate continues out to 2030, modern RE would then total 33 EJ, roughly twice its 2006 value. Higher growth rates are unlikely because of expected slower growth in hydro and modern biomass, which account for nearly 95% of the total. In a 2007 IEA assessment, the scenario most favourable for RE also assumed an approximate doubling in modern RE by 2030. In contrast, global use of fuel wood was expected to decrease in the coming decades, displaced by modern energy sources (IEA, 2007). Estimating future RE potential is more than usually complicated for several reasons. First, it often depends on technology which is not yet commercially proven. Although hydropower, biomass combustion and conventional geothermal power are mature technologies, their technical potential is limited (Pimentel et al., 2002; Moriarty and Honnery, 2007a,b, 2009). On the other hand, the RE source with by far the largest potential, direct solar, awaits fundamental technology breakthroughs for unit costs to be reduced to anywhere near existing levels. A very rough calculation illustrates the scale of the cost problem. A US report estimated that the global solar electricity market in 2005 was in excess of $US 10 billion/year (Lewis, 2007). In 2005, solar electrical energy output was 0.01 EJ. Supplying all the roughly 500 EJ of primary used globally each year with solar energy would thus cost $US 500 trillion, an order of magnitude larger than the 2006 world gross national income (World Bank, 2008). These costs in turn suggest that total input energy costs are much higher than usually calculated, resulting in little or no net energy. Already, the current economic downturn is adversely affecting PV cell sales (Sanderson, 2009). Like solar, large scale use of wind also presents challenges, although wind turbine technology is by now well developed. Current global wind energy production is less than one EJ, far below our estimated global technical potential of 229 EJ. Realizing this potential would require construction of over 24 million 2 MW turbines, roughly 500 times as many 2 MW units as are currently needed. Further, large scale use of wind and solar will require energy storage and conversion, again with further technical challenges—and added costs. Converting electricity to hydrogen which could be stored, typically results in a 45% loss (Honnery and Moriarty, 2009). Second, possible limits to RE technical potential could arise from the finite nature of some of the material inputs necessary for a given RE. This is particularly the case for solar PV cells, where
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several options are foreclosed because of the limited global reserves of needed metals (Feltrin and Freundlich, 2008). Third, ongoing climate and other environmental changes – including land-use changes – will likely adversely affect future RE technical potential and especially individual project viability, as detailed for hydro and biomass in our previous papers (Moriarty and Honnery, 2007a,b, 2009). The various forms of RE are very sensitive to adverse environmental impacts, since their assumed environmental advantages are an important reason for preferring them over fossil fuels. Not only could ongoing environmental and land-use changes reduce overall RE technical potential, but all RE sources themselves can have potentially serious environmental impacts when deployed on a large scale (see, e.g. Abbasi and Abbasi, 2000; Pimentel et al., 2002; Trainer, 2007; Babir, 2008; Cowern and Ahn, 2008; Makarieva et al., 2008; Schroder, 2008). The natural world freely provides humans – and all other living organisms – with a variety of ecosystem services, which are vital for our and their continued existence. For humans, the obvious ones are the provisioning services of food, fibre, lumber and fresh water. These in turn depend on a variety of other less-obvious regulating ecosystem services, including pest control, plant pollination and air and water quality (Millennium Ecosystems Assessment, 2005; Carpenter et al., 2009). Widely deployed, RE can act to undermine ecosystem services. Equally important, the various provisioning ecosystem services can be in conflict with each other. Particularly in the case of biomass, the expansion of renewable energy can compromise the provision of food, forestry and other fibre products, as an analysis of terrestrial net primary production (NPP) shows. NPP is a measure of the net conversion of atmospheric CO2 by photosynthesis into plant biomass (mainly natural vegetation) over a given time period, and is obtained by subtracting the autotrophic (self) respiration of plants from gross biomass production. Photosynthesis on land produces an annual total NPP of roughly 120 billion tonnes dry matter, or 1900 EJ (Moriarty and Honnery, 2007a; Field et al., 2008). Kleidon (2006) has argued that attempts to increase the global human appropriation of NPP (HANPP) much above his presentday estimate of 40% are self-defeating. His simulated results, using ‘a coupled dynamic vegetation–climate system model of intermediate complexity’ show that as the HANPP fraction grows, the absolute value of HANPP (in terms of gC/m2/day, for example) will begin to fall after reaching about 45%. In other words, since output of food, forestry and other fibre products will need to be expanded (because of ever-rising human numbers) in a world where ongoing climate changes could adversely affect output, the potential for sustainable bioenergy production could be close to zero. Likewise, Field et al. (2008) estimate that only 27 EJ of biomass energy can be harvested globally without undermining food production or worsening climate change. Further, cellulosic biomass may never be a feedstock for liquid fuels; a recent paper (Felix and Tilley, 2008) found that conversion of switchgrass to ethanol may not yield net energy. Already, global species extinction is estimated at around 12,000 per year, or 0.25% per year of all Earth’s species (Avise et al., 2008). Any expansion of HANPP will accelerate this species loss. Although biomass and hydro have the most adverse effects on the environment and its continued ability to deliver ecological services, all RE sources can be expected to have some negative effects. The negative effects of biomass and hydro may in part simply result from their already-widespread deployment, and the required 3–4 orders of magnitude scale-up of wind and solar energy could well reveal similar problems. As an example, although much has been made of bird kills by wind turbines, bat kills are far more frequent. It appears that migratory tree-roosting
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species are most at risk, but why they are killed in such numbers is uncertain (Kunz et al., 2007). These insect-eating bats help provide an important ecosystem service—pest control. Just as important as environmental effects, RE can also endanger human life. Kerr and Stone (2009) report recent research which argues that the filling of the Zipingpu hydro dam may have been responsible for the devastating 2008 Sichuan earthquake. The filling of the Koyna Reservoir in India, was judged responsible for a 1967 earthquake which killed 200 people. Although citizens’ opposition to various forms of RE installations often focuses on environmental issues to press their case, it can also result from more personal concerns. Less-pressing, perhaps, are worries that local construction of wind farms might lower real estate prices or spoil the view. But, particularly with hydro schemes in the developing countries, opposition is often motivated by well-founded fears of losing one’s home, livelihood and way of life. Such opposition arises partly because of the large land requirements for most forms of RE compared with the other two energy sources (Pimentel et al., 2002). Future use of RE is thus highly uncertain, for a variety of reasons. The optimistic technical potentials (often many thousand EJ) reported in the literature (e.g. Momirlan and Veziroglu, 2005; de Vries et al., 2007) not only depend on unprecedented technological advances, but also assume that no environmental changes adverse to RE production occur. Further, RE sources, like other energy sources, can in turn have serious environmental consequences, potentially undermining both their political support and the environmental services the natural world provides.
4. Nuclear energy At the end of 2007, some 439 nuclear power plants were in operation around the world, with a total generating capacity of 372 gigawatt (GW) supplying 9.4 EJ of electric power in 2007 (IAEA, 2008). Global proven reserves of uranium are 2.85 million tonne (MT); ultimately recoverable conventional resources are estimated at 17.1 MT. If, in the extreme case, present-day thermal reactor types had to provide 1000 EJ annually, even 17.1 MT would only last for about 10 years and 2.85 MT for less than two years (Moriarty and Honnery, 2007a). On the other hand, at present rates of annual nuclear power output, 17.1 MT would last the world for several hundred years. The IAEA (2008), in assessing the future of nuclear energy, projected that in the low-growth case, nuclear energy’s share of global electricity generation in 2030 would fall from its 2007 value of 14.2% to 12.4%. Even in their high-growth scenario, nuclear’s share would only increase to 14.4%, just above its present level. The EIA (2008) high- and low-growth projections are very similar to those of the IAEA. Both sets of forecasts were made before the current global economic downturn, and more recently one nuclear consultant predicted that ‘the industry will not even be able to replace the units being shut down because of ageing’ (Brumfiel, 2008a). The prospects for rapid growth in nuclear power are not helped by escalating construction costs; in the US the cost of planned 1 GW nuclear plants is as high as $US 10 billion (Romm, 2008). Given this low anticipated output of nuclear energy, fuel constraints are unlikely to restrict output. However, the low growth of nuclear power in recent decades, particularly in Western Europe and North America, is not only a consequence of high costs. Political opposition has led a number of countries to veto nuclear power plants, and others, such as Germany, to commit to phasing out existing programs. Other parts of the fuel cycle may also face opposition; the state of Nevada in the
US opposes construction of a nuclear waste repository at Yucca Mountain. Although opposition to nuclear power is usually labelled environmentalist, nuclear operations, with the important exception of uranium mining, have few direct effects on earth’s energy and material flows, or ecosystems. Negligible greenhouse gas emissions are released during reactor operation, although they are incurred in other parts of the fuel cycle, especially in reactor construction and uranium enrichment. Instead, opposition has been based largely on the health and safety risks to humans. These can arise from human error, as in the Chernobyl reactor accident, from deliberate human actions, such as the diversion of fissile materials for nuclear weapons, or from natural hazards. Although fires, floods and even tsunamis could conceivably affect reactor safety, earthquakes are the main hazard. In 2007, the world’s largest nuclear power complex at Kashiwazaki-Kariwa in Japan, was struck by a 6.6 magnitude earthquake. The seven reactors were undamaged, but the fault line was previously unknown to the plants’ designers. The reactors have not yet been restarted (Sacchetti, 2008). Up to 2030, only thermal reactors, chiefly modified versions of existing light water reactors, are expected to be in operation. Beyond 2030, breeder reactors are a possibility. Breeder reactors could in principle extend uranium reserves by a factor of 30, but face severe technical problems given their high operating temperatures, and significantly increased risk of nuclear proliferation (Moriarty and Honnery, 2007a, 2009). The breeding rate of new fissile material (and costs and difficulties of fuel reprocessing) could be the limiting factor on the rate of expansion. Further, like all fission reactor types, they contain a large inventory of highly radioactive materials, which could conceivably be released by a reactor accident or sabotage. Their risks to human health and safety would overall be much greater than for thermal reactors. Research on fusion energy has been in progress for half a century, but fusion is still nowhere near commercial realisation, which, if it ever occurs, will not be before the last quarter of this century. The favoured approach is confining deuterium–tritium plasma in a toroidal magnetic field. While this approach may be superior from a physics viewpoint, the engineering problems are daunting, mainly because of the intense neutron flux and its effect on the blanket-shield and the reactor structural materials (Parkins, 2006). Electricity costs will be higher, possibly many times higher, than for existing fission-based electricity (Hirsch, 2003). With its rising capital costs and lack of private investor interest, nuclear power of any type will be struggling to maintain its existing output levels.
5. Policy implications Most energy analysts think that global primary energy use in the decades to come will be much higher than present levels, with projections for the year 2050 often 1000 EJ or more. Even the IEA (2008b) projections, which take into account the current global economic downturn, foresee 2030 primary energy of 712 EJ in the base case. Yet the energy sources that singly or together must meet this projected demand – fossil fuels, RE, and nuclear power – all face three categories of possible limitations, namely:
Physical limits such as geological limits on fossil fuel reserves. Political, economic, technical or social constraints on their production.
Environmental constraints on their production or use. These categories are not independent of each other, but can interact. Fears of impending fossil fuel reserve depletion could
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encourage either energy-exporting or -importing countries to limit production/use below that possible at that time. Similarly, environmental problems from energy production or use (especially CO2 emissions from fossil fuels) could hasten moves by citizen groups or policy-makers to limit its use. Advocates for high future energy use often acknowledge that much of this energy will need to come from technologies not yet commercial, and sometimes not even at the demonstration stage. They can point to the remarkable technical advances over the past century as reasons for optimism, but such optimism about new energy sources may be misplaced, for several reasons. First, in contrast to advances in information technology, experience shows that new energy sources are usually more costly than anticipated, and take much longer to gain a significant market share. Second, new technologies will increasingly be subjected to constraints on their use: for instance, they may require materials in scarce supply, their large-scale deployment may uncover novel environmental problems, or ongoing changes in global land-use and climate may reduce their potential for use. Our analysis so far suggests that even holding primary, and even more so delivered energy, at present levels in 2050 will prove difficult. Several implications for policy follow. First, we will need to avoid as far as possible the use of non-conventional fossil fuels, since these have higher than average primary/secondary energy ratios, and thus higher environmental damages, including CO2 emissions per unit of secondary energy. A second, related, point is the need to avoid carbon capture (especially air capture) and sequestration, as this will likewise increase the primary/ secondary energy ratio. Attempts to maintain, let alone raise, secondary energy output will thus also hasten fossil fuel depletion. We have argued elsewhere that restricting annual use of primary energy from fossil fuels to 50–100 EJ would both remove the need for carbon capture and storage and also permit use of fossil fuels for several centuries (Moriarty and Honnery, 2009). It would also reduce the need for large increases in nonconventional fossil fuel use. The third policy implication is that we should delay for as long as possible the need for conversion and storage of intermittent RE sources—mainly wind and solar energy. We have so far only discussed energy from a global viewpoint, but, of course, countries differ greatly in their energy resource endowments. If modern RE only doubles by 2030, as suggested above, and electricity use grows as forecast, grid integration of intermittent RE is unlikely to be a serious technical problem in any country. But given the limited potential of baseload RE, the cost and risk problems facing nuclear fission expansion, and the desirability – and perhaps need – to reduce fossil fuel use, the share of intermittent electricity in grids could grow rapidly. Also, if wind/ solar electricity expand more rapidly than anticipated, the need for conversion/storage will be brought forward; if this is not possible, electricity grid management practices will need to be changed. Without either of these two interventions, the nature of the existing electricity grid will ultimately limit intermittent RE production. The current use of fossil fuels brings about another problem. Since fossil fuels dominate our existing energy system, they will have to power any possible shift to RE or nuclear sources. The effect this has on fossil fuel reserves will depend largely on the size and speed of the shift, since fossil fuel energy used will be additional to that already in use. If changes to climate warrant a decisive shift to RE within the next decade, this shift would not only hasten depletion of fossil fuels, but could also hasten climate change. If the shift to RE was powered by RE alone, it is likely the rate of change would be too small; we would possibly see significant climate problems or face fossil fuel depletion before RE could supply large amounts of primary energy.
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Clearly, there are no easy choices facing future production and use of energy for most countries. Even if fossil fuel reserves are closer to the optimist position, there is no guarantee that political or environmental constraints, particularly the need for greenhouse gas emission reductions, will not greatly limit annual output. But if deep cuts are made to fossil fuel use, the resulting large spare capacity will slow change away from fossil fuel power plants. Only large reductions in global primary energy use, with all its difficulties of implementation, can meet the resource, environmental, economic and political problems that future energy use will face.
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