A Survey of our Energy Supply

We are enmeshed in a multi-dimensional problem of our own making. The answer to the question of our future energy depends on many variables. We need to consider how we will deal with the other intertwined variables of the environment (particuliarly global warming) and economics as well. Our future use of fossil fuels is severely constrained by the environmental tipping point of global warming and our future per capita energy consumption will largely depend on what the system that will replace our current unsustainable model of perpetual economic growth.

How much energy our society will need in the future will therefore depend on a number of factors:

  1. are we willing to use far less energy per capita in the future?
  2. economic reform: will we abandon our mantra of continuous growth and if so, what will we replace it with?
  3. how much clean energy is available?
  4. how much more CO2 emissions can we emit?

Fossil Fuel Energy Supply will be Severely Constrained in the Future

The future of our energy supply is intimately connected to climate change. If we are to continue to take a business-as-usual approach with fossil fuel consumption, the scientific consensus is an uncertain future for human civilization and much of life as we know it today on our planet. Politicians have adopted the target of avoiding a 2 degree C rise above pre-industrial levels as the minimum temperature threshold. Most scientists feel that it should be 1 degree C but this is impossible to achieve; as of July 2012, the planet is already at 0.8 degree C and even if we were to stop all CO2 emissions in July 2012, conservative estimates are that the inertia of CO2 already in the atmosphere would push temperatures to 1.6 degree C by 2050.

Studies show that the missing heat in the last decade is actually being stored in the deep oceans. What happens when the oceans have reached their capacity to store all that additional heat energy?…it will spill over into the atmosphere, further exacerbating the already large challenges we face.

Research by the Potsdam Institute calculates that to reduce the chance of exceeding 2°C warming to 20%, the global carbon budget for 2000-2050 is 886 GtCO2. Subtracting emissions from the first decade of this century, this
leaves a budget of 565 GtCO2 for the remaining 40 years to 2050. This puts the energy industry in a very precarious position.



Figure 1: Carbon Tracker Comparison of the global 2°C carbon budget with total fossil fuel reserves CO2 emissions potential


The report  Unburnable Carbon, Are the world’s financial markets carrying a carbon bubble?  produced by Carbon Tracker spells out clearly the dilemma that the fossil fuel industry faces. The market valuation of most fossil fuel companies are based upon huge future reserves of carbon – reserves that are still in the ground. The Unburnable Carbon report confirms that only a fifth of all known reserves can be burned, any more will exceed the 2 Degree limit agreed to at the Copenhagen climate summit in 2009.

The fossil fuel industry is stuck between a rock and a hard place and it is no wonder that these companies, motivated by profit have no choice but to embrace climate change denialism. Fossil fuel industry leaders know that the fossil fuel industry is beginning to wind down; they can clearly read the writing on the wall.  Intense lobbying and deception by Exxon Mobil, the Koch brothers and other energy players is a stalling tactic that buys the industry more time to extract as much oil and gas reserves as possible.  Their current strategy is tantamount to sticking their heads in the sand and ignoring all the science – because of greed.  In essence, the industry is feeling its very life is being threatened and has adopted a fear-based response and an approach of “let’s profit as quickly before regulation or market demand for fossil fuel dries up”.  A more constructive approach would be to use their vast accumulations of wealth to transform the entire energy landscape. If they did, they can become the industry leaders of the new era. They have the capital to do it, but, unfortunately not the foresight.

Fortunately there are activists such as environmentalist Bill Mckibben and his organization 350.org who are going to make sure that unburnable carbon remains just that. The battle lines have been drawn. The people of the planet are on a collision course with the fossil fuel industry. We are  fighting to keep 80% of these reserves in the ground while the fossil fuel industry is fighting to exploit it all as fast as they can.

Financial / Investment Community Reaction

According to the most likely projections by climate scientists, “at least one-half of fossil fuel assets will have to be left in the ground,” said Nick Robins, head of the HSBC climate change centre of excellence in London. “We’re still pricing [companies in the extractives sector] as if they are all going to be exploited.” “This is a particular concern for the UK as our stock market is overweight fossil fuels,” he said, creating the risk of stranded assets. The comments were made at a recent ACCA / NSFMevent reported by Environmental Finance.

“We now have around 7 trillion subprime carbon assets in the global economy and their value, like the subprime mortgages, is based on an assumption that is highly questionable.” – Al Gore

“Valuations of the oil and gas sector still assume that they will be able to take all proven and probable reserves out of the ground and burn them. Based on credible data we cannot be allowed to do that,” – Aviva Investors

The Grantham Institute, working with Carbon Tracker has released a 2013 report that reveals that fossil fuel reserves in 2013 already far exceed the carbon budget to avoid global warming of 2°C, but in spite of this, the fossil fuel industry spent $674billion in 2012 to find and develop new potentially stranded assets. This report indicates an industry in denial.

One Analysis on Future Energy Needs

While there is a growing movement to keep unburnable carbon in the ground, scientists around the world are working feverishly to try to find new energy solutions. Nathan Lewis and his Lewis Research Group at University of California Berkeley have done extensive calculations and analysis on global energy requirements, present and future with the object of finding viable replacements for fossil fuel to meet future demands. While Lewis himself is specialized in one specific energy solution, solar chemical, his analysis is broad-based. The following energy analysis is from  Powering the planet: Chemical challenges in solar energy utilization .

To determine if there is a viable carbon-free replacement for fossil fuel, we need to answer the following questions:

  1. what amounts do we currently consume?
  2. what will we need in the future?
  3. what sources will supply these needs?

What do we consume?

Figure 1. Breakdown of 13.8 Terra Watts Global Power Consumption in 2001 (Source: Lewis et al, Powering the planet: Chemical challenges in solar energy utilization, 2006)

 The pie chart above shows 2001 Global Consumption of Energy. In particuliar:

 Note that this is from 2006 and figures have changed in the past 6 years. Notably, the Internatonal Energy Agency estimates for reserves as of 2011 projects that another 4 Saudia Arabia’s must be discovered to keep up with demand – something which it thinks is unlikely to happen.

Lewis begins his analysis with projected energy requirements and then looks at all the possible low carbon alternatives that can meet this demand.

What will we need?

Figure 4: IEA global energy consumption 2009 (Source: IEA)

Figure 5: IEA global energy consumption 2050 (Source: IEA)

(Source: Lewis et al, Powering the planet: Chemical challenges in solar energy utilization, 2006)

  • Future energy demand is projected to increase considerably relative to that in 2001.
  • The most widely used scenarios for future world energy consumption have been those developed by the Intergovernmental Panel on Climate Change, an organization jointly established by the World Meteorological Organization and the United Nations Environment Program (after Scenario B2)
  • E˙ =  (869 EJ/yr)*(106TJ/EJ)*(60*60*24*365 s/yr) =27.54 TW (TJ, terajoule; and EJ, exajoule)
  • The scenario outlined in the last two columns of Table 1 is based on ‘‘moderate’’ assumptions and hence is reasonably viewed as neither overly conservative nor overly aggressive

To better understand this scenario, the top half of Table 1 breaks down the rate of energy consumption, E˙, into three fundamental factors:

E˙ = N*(GDP/N)*(E˙/GDP)


  1. N is the global population
  2. GDP/N is the globally averaged gross domestic product (GDP) per capita
  3. E˙/GDP is the globally averaged energy intensity (i.e., the energy consumed per unit of GDP)
Figure 2: N, GDP/N and E/GDP (Source: Powering the Planet, Nathan Lewis)
Figure 3: Carbon Intensity (Source: M. I. Hoffert et. al., Nature, 1998, 395, 881)
  • The world population was 6.1 billion in 2001, reached 7 billion in 2011 and in the scenario represented in Table 1, the global population is projected to increase by 0.9%/yr to 9.4 billion by 2050
  • World per capita GDP was $7,500 per capita in 2001.
  • In the Table 1 scenario, GDP/N is projected to increase at the historical average rate of 1.4% /yr to $15,000 per capita by 2050
  • No country has a policy against economic growth, so this increase in GDP/N seems quite reasonable and in fact may well be modest given the rapid economic growth being experienced by China and India at present
  • With no changes in the globally averaged energy intensity, the world energy consumption rate would grow, due to population growth and economic growth, by 2.3% /yr, from 13.5 TW in 2001 to 40.8 TW in 2050
  • However, the global average energy intensity has declined continuously over the past 100 yr, due to improvements in technology throughout the energy production, distribution, and end use chain. In anticipation of continued improvements in technology, the global average energy intensity in the Table 1 scenario is projected to decrease at approximately the historical average rate of 0.8% /yr, from 0.29 W$/yr in 2001 to 0.20 W$/yr by 2050.
  • This decrease offsets somewhat the projected increases in population and per capita GDP, so that the world energy consumption rate is instead projected to grow by:  2.3% /yr- 0.8% /yr =  1.5% /yr  from 13.5 TW in 2001 to  27 TW by 2050
  • Hence, even factoring in a decrease in energy intensity, the world energy consumption rate is projected to double from 13.5 TW in 2001 to 27 TW by 2050 and to triple to 43 TW by 2100
  • Without policy incentives to overcome socioeconomic inertia, development of needed technologies will likely not occur soon enough to allow capitalization on a 10-30 TW scale by 2050
  • Researching, developing, and commercializing carbon-free primary power technologies capable of 10-30 TW by the mid-21st century could require efforts, perhaps international, pursued with the urgency of the Manhattan Project or the Apollo Space Program.”

(Source: Lewis et al, Powering the planet: Chemical challenges in solar energy utilization, 2006)

Estimated Reserves of Global Carbon Stock

Lewis cites the World Energy Assessment Report estimates of the total reserves (i.e., 90% confidence that the reserves exist) and of the global resource base, including both conventional and unconventional sources as benchmarks for evaluating the total available global fossil energy base:

Based on 1998 consumption rates:

  • 40–80 yr of proven conventional and unconventional oil reserves exist globally
  • 50–150 yr of oil are available if the estimated resource base is included
  • 60 to 160 yr of reserves of natural gas are present
  • between 207 and 590 yr of gas resources, not including the natural gas potentially available as methane clathrates in the continental shelves
  • 1,000- to 2000-yr supply of coal, shales, and tar sands is in the estimated resource base

Hence the estimated fossil energy resources could support a 25- to 30-TW energy consumption rate globally for at least several centuries.

Fossil Fuel Usage is limited by Global Warming

Unfortunately, even if such supplies exist, we cannot continue burning dirty carbon fuels due to the increased effect on global warming due.

  1. Historically, the mean carbon intensity (kg of C emitted to the atmosphere as CO2 per year per W of power produced from the fuel) of the global energy mix has been declining.
  2. In the past two centuries, the energy mix has shifted from being dominated by wood to coal to oil and now more to natural gas
  3. This shift has produced a decrease in the average carbon intensity of the energy mix, because oil and gas have higher HC ratios and hence upon combustion produce more water and less CO2 per unit of heat released than does coal
  4. If the carbon intensity were to remain at the year 2001 value (approximately equal parts coal, oil, and natural gas), the world carbon emission rate would grow due to the projected growth in the energy consumption from 6.6 billion metric tons of carbon (GtC)/ yr in 2001 to 13.5 GtC/yr by 2050.
  5. The IPCC ‘‘business as usual’’ scenario of Table 1 projects, arguably optimistically, that the historical trend of mean carbon intensity decline with time will continue through 2050, producing an energy mix continually favoring cleaner burning fuels from a carbon emissions viewpoint, until the average in 2050 is below that of the least carbon-intensive fossil energy source, natural gas.
  6. This decrease in carbon intensity would offset somewhat the increase in the rate of energy consumption. But even with this projected decrease in carbon intensity, the world carbon emissions rate in this scenario is projected to nearly double from 6.6 GtC/yr in 2001 to 11.0 GtC/yr by 2050.
  7. On the timescale of many centuries, CO2 emissions are essentially cumulative in the atmosphere
  8. The CO2 equilibrates on an 10- to 30-yr timescale between the atmosphere and the near-surface layer of the oceans, which accounts for why only 50% of the anthropogenic CO2 emissions remain in the atmosphere (the remainder partitioning into the biosphere and the oceans)
  9. Because there are no natural destruction mechanisms of CO2 in the atmosphere, the long-term removal of atmospheric CO2 must occur by convection
  10. The relevant mixing time between the nearsurface ocean layer and the deep oceans is between 400 and several thousand years
  11. Hence, in the absence of geoengineering or active intervention, whatever environmental effects might be caused by this atmospheric CO2 accumulation over the next 40–50 yr will persist globally for the next 500–2,000 yr or more.
  12. Although the precise future effects of such anthropogenic CO2 emissions are still somewhat uncertain, the emission levels can certainly be viewed rigorously within a historical perspective. The data from the Vostok ice core indicate that the atmospheric CO2 concentration has been between 210 and 300 ppm for the past 420,000 yr, and more recent studies of Dome Concordia ice cores have extended this time period to 650,000 yr.
  13. Over this same time period, the atmospheric CO2 concentration has been highly correlated with, but is not necessarily the cause of, temperature swings that have repeatedly caused ice ages on the planet
  14. The CO2 concentrations in the past 50 yr have been rising because of anthropogenic CO2 emissions from fossil fuel consumption, and they are now approaching 400 ppm.
  15. Without intervention, even the Table 1 scenario produces, within the 21st century, atmospheric CO2 concentrations that are more than double the pre-anthropogenic values
  16. The exact levels vary depending on the assumed composition of energy sources, the efficiency of energy production and consumption, the global economy, and different intervention scenarios to control CO2 levels.
  17. Modestly stringent interventions are based on stabilizing atmospheric CO2 in the 550- to 650-ppm range, with substantially higher values projected (750 ppm) if the Table 1 scenario is followed
  18. Climate models predict a variety of different harmful global responses to levels of CO2 at or in excess of 550 ppm in the atmosphere
  19. In some models, moderate changes are predicted, whereas in others, relatively serious sea level rises, changes in the hydrological cycle, and other effects are predicted
  20. Tipping points involving positive feedback, such as the accelerated loss of permafrost, which could release further CO2 which then could accelerate still further permafrost loss, are of substantive concern
  21. What can be said with certainty is that the atmospheric CO2 concentrations are being increased and without severe intervention will continue to increase, because of anthropogenic sources, to levels that have not been present on the planet in at least the past 650,000 yr and probably in the past 20 million yr
  22. Four-fifths of the total energy-related CO2 emissions permissible by 2035 in the 450 Scenario are already “locked-in” by our existing capital stock (power plants,  buildings, factories, etc.). If stringent new action is not forthcoming by 2017, the energy-related infrastructure then in place will generate all the CO2 emissions allowed in the 450 Scenario up to 2035, leaving no room for additional power plants, factories and other infrastructure unless they are zero-carbon, which would be extremely costly.  Delaying action is a false economy: for every $1 of investment avoided in the power sector before 2020 an additional $4.3 would need to be spent after 2020 to compensate for the increased emissions.

(Source: 1 -21: Lewis et al, Powering the planet: Chemical challenges in solar energy utilization, 2006, 22: IEA World Energy Outlook 2011 Executive Summary )

How will our Energy Consumption look like in the Future?

Richard Heinberg is a fellow of the Post Carbon Institute and his view is that we must get use to a low energy future. We are in a phase-out period of hydrocarbons but we haven’t got any energy source that is sufficiently concentrated and clean to replace it. Others may differ with this view (usually technocrats that depend on science to come to the rescue…see Options for our Future  or Renewable Energy page. In this April 16, 2013 post from the Post Carbon Institute, Heinberg argues for a society that must adjust itself to a far lower energy future.

There’s Only One Real Option for Averting Economic and Ecological Ruin — So Why Aren’t We Talking About It?

Energy conservation is our best strategy for pre-adapting to an inevitably energy-constrained future. And it may be our only real option for averting economic, social, and ecological ruin. The world will face limits to energy production in the decades ahead regardless of the energy pathway chosen by policy makers. Consider the two extreme options—carbon minimum and carbon maximum.

If we rebuild our global energy infrastructure to minimize carbon emissions, with the aim of combating climate change, this will mean removing incentives and subsidies from oil, coal, and gas and transferring them to renewable energy sources like solar, wind, and geothermal. Where fossil fuels are still used, we will need to capture and bury the carbon dioxide emissions.

We might look to nuclear power for a bit of help along the way, but it likely wouldn’t provide much. The Fukushima catastrophe in Japan in 2011 highlighted a host of unresolved safety issues, including spent fuel storage and vulnerability to extended grid power outages. Even ignoring those issues, atomic power is expensive, and supplies of high-grade uranium ore are problematic.

The low-carbon path is littered with other obstacles as well. Solar and wind power are plagued by intermittency, a problem that can be solved only with substantial investment in energy storage or long-distance transmission. Renewables currently account for only a tiny portion of global energy, so the low-carbon path requires a high rate of growth in that expensive sector, and therefore high rates of investment. Governments would have to jump-start the transition with regulations and subsidies—a tough order in a world where most governments are financially overstretched and investment capital is scarce.

For transport, the low-carbon option is even thornier. Biofuels suffer from problems of high cost and the diversion of agricultural land, the transition to electric cars will be expensive and take decades, and electric airliners are not feasible.

Carbon capture and storage will also be costly and will likewise take decades to implement on a meaningful scale. Moreover, the energy costs of building and operating an enormous new infrastructure of carbon dioxide pumps, pipelines, and compressors will be substantial, meaning we will be extracting more and more fossil fuels just to produce the same amount of energy useful to society—a big problem if fossil fuels are getting more expensive anyway. So, in the final analysis, a low-carbon future is also very likely to be a lower-energy future.

What if we forget about the climate? This might seem to be the path of least resistance. After all, fossil fuels have a history of being cheap and abundant, and we already have the infrastructure to burn them. If climate mitigation would be expensive and politically contentious, why not just double down on the high-carbon path we’re already on, in the pursuit of maximized economic growth? Perhaps, with enough growth, we could afford to overcome whatever problems a changing climate throws in our path.

Not a good option. The quandary we face with a high-carbon energy path can be summed up in the metaphor of the low-hanging fruit. We have extracted the highest quality, cheapest-to-produce, most accessible hydrocarbon resources first, and we have left the lower quality, expensive-to-produce, less accessible resources for later. Well, now it’s later. Enormous amounts of coal, oil, gas, and other fossil fuels still remain underground, but each new increment will cost significantly more to extract (in terms of both money and energy) than was the case only a decade ago.

Figure 4: EROI Chart

After the Deepwater Horizon oil spill of 2010 and the Middle East–North Africa uprisings of 2011, almost no one still believes that oil will be as cheap and plentiful in the future as it was decades ago. For coal, the wake-up call is coming from China—which now burns almost half the world’s coal and is starting to import enormous quantities, driving up coal prices worldwide. Meanwhile, recent studies suggest that global coal production will max out in the next few years and start to decline.

New extraction techniques for natural gas (horizontal drilling and “fracking”) have temporarily increased supplies of this fuel in the United States, but the companies that specialize in this “unconventional” gas appear to be subsisting on investment capital: Prices are currently too low to enable them to turn much of a profit on production. Costs of production and per-well depletion rates are high, and energy returns on the energy invested in production are low. Recent low prices resulted from a glut of production produced by rampant drilling in 2005–2007, which only made economic sense when gas prices were much higher than they are now. All of this suggests that rosy expectations for what “fracking” can produce over the long term are overblown.

Exotic hydrocarbons like gas hydrates, bitumen (“tar sands”), and kerogen (“oil shale”) will require extraordinary effort and investment for their development and will entail environmental risks even higher than those for conventional fossil fuels. That means more expensive energy. Even though the resource base is large, with current technology the nature of these materials means they can be produced only at relatively slow rates.

But if the hydrocarbon molecules are there and society needs the energy, won’t we just bite the bullet and come up with whatever levels of investment are required to keep energy flows growing at whatever rate we need them? Not necessarily. As we move toward lower-quality resources (conventional or unconventional), we have to use more energy to acquire energy. As net energy yields decline, both energy and investment capital have to be cannibalized from other sectors of society in order to keep extraction processes expanding. After a certain point, even if gross energy production is still climbing, the amount of energy yielded that is actually useful to society starts to decline anyway. From then on, it will be impossible to increase the amount of economically meaningful energy produced annually no matter what sacrifices we make. And the signs suggest we’re not far from that point.

In one sense it matters a great deal whether we choose the low-carbon or the high-carbon path: One way, we lay the groundwork for a sustainable (if modest) energy future; the other, we destabilize Earth’s climate, shackle ourselves ever more tightly to energy sources that can only become dirtier and more expensive as time goes on, and condemn myriad other species to extinction.

However, in another sense, it doesn’t matter which path we choose: With human population numbers growing and energy constraints looming, we will have less energy to burn per capita in the future. Plot any scenario between the low-carbon and high-carbon extremes and that conclusion still holds, which means less energy for transport, for agriculture, and for heating and cooling homes. Less energy for making and using electronic gadgets. Less energy for building and maintaining cities.

Efficiency can help us obtain greater services for each unit of energy expended. Research has been proceeding for decades on how to reduce energy inputs for all sorts of processes and activities. Just one example: The electricity needed for illumination has declined by up to 90 percent due to the introduction first of compact fluorescent light bulbs, and now LED lights. However, efficiency efforts are subject to the law of diminishing returns: We can’t make and transport goods with no energy, and each step toward greater efficiency typically costs more. Achieving 100 percent efficiency would, in theory, require infinite effort. So while we can increase efficiency and reduce total energy consumption, we can’t do those things and produce continual economic growth at the same time.

Humanity is at a crossroads. Since the Industrial Revolution, cheap and abundant energy has fueled constant economic growth. The only real discussion among the managerial elite was how to grow the economy—whether in planned or unplanned ways, whether with sensitivity to the natural world or without.

Now the discussion must center on how to contract. So far, that discussion is radioactive—no one wants to touch it. It’s hard to imagine a more suicidal strategy for a politician than to base his or her election campaign on the promise of economic contraction. Denial runs deep, but sooner or later reality will expose the delusion that endless growth is possible on a finite planet.

Sooner or later we must make conservation the centerpiece of economic and energy policy. The term “conservation” implies efficiency—building cars and appliances that use less energy while delivering the same services. But it also means cutting out nonessential uses of energy. Rather than continuing to increase economic demand by stimulating human wants, we must begin to think about how to meet basic human needs with minimum consumption of resources, while discouraging extravagance.

If we move toward renewable and intermittent energy sources, a larger portion of society’s effort will have to be spent on processes of energy capture. Energy production will require more land and a greater proportion of society’s total labor and investment. We will need more food producers, but fewer managers and salespeople. We will be less mobile, and each of us will own fewer manufactured products—though of higher quality—which we will reuse and repair as long as possible before replacing them.

The transition to a more durable and resilient but lower-energy economy will go much better if we plan it. Wherever it is possible for households and communities to pre-adapt, and wherever clever people are able to show innovative ways of meeting human needs with a minimum of consumption, there will be advantages to be enjoyed and shared.

Much of the current public discussion about our energy future tends to turn on the questions of which alternative energy sources to pursue and how to scale them up. But it is even more important to broadly reconsider how we use energy. We must strategize to meet basic human needs while using much less energy in all forms. Since this will require major societal effort sustained over decades, it is important to start implementation of conservation strategies well before actual energy shortages appear.

With regard to our food system, it is essential to understand that lower energy inputs will result in the need for increased labor. Thus the energy transition could represent economic opportunity for millions of young farmers. Agricultural production must be adapted to substantially reduced applications of nitrogen fertilizer and chemical pesticides and herbicides since these will grow increasingly expensive as their fossil fuel feedstocks rise in price. And higher transport energy costs mean that food systems must be substantially relocalized.

Transport systems must be adapted to a regime of generally lowered mobility and increased energy efficiency. This would most likely require widespread reliance on walking and bicycling, with remaining motorized transport facilitated by car-share and ride-share programs. Electric vehicles and rail-based public transport systems should be favored, and new highway construction halted.

Reduced overall mobility will require substantial changes in urban design practice and land use policies. Neighborhoods within cities must become more self-contained, and cities must be reintegrated with adjacent productive rural areas. Buildings—including tens of millions of homes in the United States alone—must be retrofitted with insulation to minimize the need for heating and cooling energy. New buildings must require net zero energy input. Incentives for installing residential solar hot water systems, and using solar cookers and clotheslines, should be effective and widespread.

Most new sources of energy will produce electricity—and in the cases of solar and wind, electricity will be produced only intermittently. Electricity storage systems (such as pumped water or compressed air) must be built to overcome at least some of the problems of intermittency. Reconfiguration of electricity grids, distributed generation, and alignment of household and industrial energy usage patterns to fit intermittent power availability are other strategies for adaptation.

The historically close relationship between increasing energy use and economic growth suggests that the global economy probably cannot continue to expand as world energy production falters. Therefore, adaptive measures must include efforts to restructure the economy to meet basic human needs and support improvements in quality of life while reducing debt and reliance on interest and investment income. Family planning must be encouraged, as adding more people to a stagnant or shrinking economy simply means there will be less for everyone.

The costs to ecological integrity and to human health of the ever-increasing scale of society’s production and transport systems have become the subject of broadening concern in recent decades. Air and water pollution, resource depletion, soil erosion, and biodiversity loss are just some of those costs. With reduced energy use must come the realization that the scale of our human presence on the planet must be appropriate to the Earth’s limited budgets of water, energy, and biological productivity.

Altogether, this will constitute a historic shift away from continual societal growth and toward conservation. It will not be undertaken except by necessity, but necessity is inevitably approaching. Barring some technological miracle, we will have less energy, like it or not. And with less energy, we will no longer be able to operate a consumer society. The kind of society we will be able to operate will almost certainly be as different from the industrial society of recent decades as that was from the agrarian society of the nineteenth century.

But suppose this analysis is wrong, or that a new miracle technology appears, and energy proves to be abundant rather than scarce. Even then, conservation makes sense: Increasing energy use leads to greater consumption of natural resources of all kinds, and the degradation of wild natural systems. Sooner or later we must rein in consumption—and since signs of ecological decline are already frighteningly prevalent, sooner is clearly better than later.

The shift to a conserver society could hold benefits for people as well as for nature. As we begin to measure success not by the amount of our consumption, but by the quality of our culture, the beauty of the built environment, and the health of ecosystems, we could end up being significantly happier than we are today, even as we leave a far smaller footprint upon our finite planet. But those benefits will be delayed and diluted for as long as we deny the conservation imperative. – Richard Heinberg, Fellow of the Post Carbon Institute

Are there viable options? 

  1. To meet the optimistic IPCC projection in the Table 1 scenario for the average carbon intensity in 2050, the projected carbon intensity in 2050 is 0.45 kg of C/ W*yr, which is lower than that of any of the fossil fuels
  2. The only way one can reach this value of the mean carbon intensity is through a significant contribution of carbon-free power to the total energy mix
  3. This conclusion holds for an economy entirely based on natural gas; to the extent that the mix of consumed fossil fuels is not 100% natural gas but is roughly also equal parts oil and coal, even more carbon-free energy is required to maintain the average of the energy mix at the 0.45 kg of C /W*yr value
  4. In fact, the amount of carbon-free power required in 2050 to meet these carbon intensity targets is 10 TW and is much greater than 10 TW if emissions are to be lowered such that CO2 can be stabilized at 550 ppm
  5. Even more carbon-free power will be required later in the 21st century if CO2 levels are to be kept below 550 ppm or if a lower atmospheric CO2 target level is desired
  6. By almost any reasonable estimate, stabilization of atmospheric CO2 levels at 550 ppm or lower will require as much carbon-neutral power by approximately the year 2050 as the amount of power produced at present from all energy sources combined
  7. Furthermore, because CO2 emissions are cumulative on a century-level timescale, even higher levels of carbon-neutral power are required by 2050 if their introduction does not start immediately with a constant rampup but instead are delayed by 20 yr for their commissioning while awaiting technology development and/or policy and socioeconomic interventions.

1. Nuclear Fission

Nuclear fission would require widespread implementation of breeder reactors

Estimated terrestrial U resources are sufficient to produce 100 TW/yr of electricity using conventional once-through U reactor technology

Hence, if 10 TW of power were obtained from conventional nuclear fission, the terrestrial U resource base would be exhausted at that level in less than a decade (in fact, it would be exhausted after the first 30 yr of reactor construction because of the fuel consumed during the rampup phase)

Moreover, construction of nuclear power plants would need to proceed at a very rapid rate by historical standards: one1-GWe (gigawatt-electric) power plant every 1.6 days for the next 45 yr

2. Nuclear Fusion

  1. The international tokamak (magnetic confinement fusion) experiment (ITER) is now scheduled to demonstrate an energy breakeven point in 35 yr for a few minutes of operational time
  2. Although fusion might possibly provide significant commercial energy late in the 21st century, the ITER time line is much too far in the future to provide a credible option to make a significant contribution to the amount of cost-effective carbonneutral energy production needed to meet any reasonable atmospheric CO2 concentration target in the next 40–50 yr

3. Carbon Capture

  1. The carbon dioxide is dissolved in underground aquifers
  2. To be a viable option technically, the CO2 must not leak at a globally averaged rate of 1% for a timescale of centuries, otherwise, the emitted flux will be greater than or equal to that intended to be mitigated initially
  3. Experiments at scale are needed, along with extensive modeling, simulation, monitoring, and validation, to ascertain with 99% confidence that the leak rate will be acceptably low for a 500- to 1,000-yr period
  4. Furthermore, each reservoir is different geologically, so proof that sequestration works technically at one reservoir is not general proof that the process will work at the required level globally
  5. The global reservoir capacity has been estimated to be equivalent to 100–150 yr of carbon emissions
  6. Hence, sequestration could buy time if it works technically and is so validated within the next 10–20 yr
  7. An additional condition is that the energy distribution and end-use chain must be transformed to handle massive quantities of carbon-free fuels (hydrogen) or electricity on the needed timescale to mitigate carbon emissions

3. Renewable Energy

  1. Of the various renewable energy sources, by far the largest resource is provided by the sun
  2. More energy from sunlight strikes the earth in1 hr (4.3 x 10 exp 20 J) than all of the energy currently consumed on the planet in 1 yr (4.1 x 10exp 20 J in 2001)
  3. Yet, in 2001, only 0.1% of electricity and 1.5% of fuels (mostly from biomass) were provided by a solar source
  4. Against the backdrop of the daunting carbon-neutral energy needs of our global future, the large gap between our present use of solar energy and its enormous undeveloped potential defines a compelling imperative for science and technology in the 21st century

(Source: Lewis et al, Powering the planet: Chemical challenges in solar energy utilization, 2006)

A Quick Look at the Role of Renewables

Can Renewables fill in for fossil fuels?  The answer is not so simple to answer because it depends on what we as a society plan to do. Most likely, we will need a combination of fossil fuel and renewables. The conservative IEA projects that a majority of our energy supply will still be provided by fossil fuel by 2050. However, projects such as Desertec, based purely on renewables suggest that the world can be powered exclusively on renewables if we have the will to scale globally.

The future will probably be manageable with a combination of new forms of renewable energy and lowered per capita energy consumption. The question is explored more fully here.

With that in mind, we look at some forms of renewable energy below.



  • Gross theoretical potential 4.6 TW
  • Technically feasible potential 1.5 TW
  • Economically feasible potential 0.9 TW
  • Installed capacity in 1997 0.6 TW
  • Production in 1997 0.3 TW

(can get maximum of 80% capacity)
Source: WEA 2000

  •  Mean terrestrial geothermal flux at earth’s surface 0.057 W/m2
  • Total continental geothermal energy potential 11.6 TW
  • Oceanic geothermal energy potential 30 TW
  • Wells “run out of steam” in 5 years
  • Power from a good geothermal well (pair) 5 MW
  • Power from typical Saudi oil well 500 MW
  • Needs drilling technology breakthrough

(from exponential $/m to linear $/m) to become economical)



  • Downward kinetic energy flux: 2 W/m2
  • Total land area: 1.5×1014 m2
  • Hence total available energy = 300 TW
  • Extract <10%, 30% of land, 30% generation efficiency:
  • 2-4 TW electrical generation potential


  • Theoretical: 27% of earth’s land surface is class 3 (250-300 W/m2 at 50 m) or greater
  • If use entire area, electricity generation potential of 50 TW
  • Practical: 2 TW electrical generation potential (4% utilizationof !class 3 land area, IPCC 2001)
  • Off-shore potential is larger but must be close to grid to be interesting; (no installation > 20 km offshore now)

Global: Top Down

  • Requires Large Areas Because Inefficient (0.3%)
  • 3 TW requires ” 600 million hectares = 6×1012 m2
  • 20 TW requires ” 4×1013 m2
  • Total land area of earth: 1.3×1014 m2
  • Hence requires 4/13 = 31% of total land area

Global: Bottom Up

  • Land with Crop Production Potential, 1990: 2.45×1013 m2
  • Cultivated Land, 1990: 0.897 x1013 m2
  • Additional Land needed to support 9 billion people in 2050:0.416×1013 m2
  • Remaining land available for biomass energy: 1.28×1013 m2
  • At 8.5-15 oven dry tonnes/hectare/year and 20 GJ higher heating value per dry tonne, energy potential is 7-12 TW
  • Perhaps 5-7 TW by 2050 through biomass (recall: $1.5-4/GJ)
  • Possible/likely that this is water resource limited
  • 14% of U.S. corn provides 2% of transportation fuel
  • Challenges for chemists: cellulose to ethanol; ethanol fuel cells

Solar Energy Potential

  • Theoretical: 1.2×105 TW solar energy potential (1.76 x105 TW striking Earth; 0.30 Global mean albedo)Energy in 1 hr of sunlight ´ 14 TW for a year
  • Practical: ” 600 TW solar energy potential (50 TW – 1500 TW depending on land fraction etc.; WEA 2000)
  • Onshore electricity generation potential of “60 TW (10% conversion efficiency): Photosynthesis: 90 TW

 Solar Thermal 2001

  • Roughly equal global energy use in each major sector: transportation, residential, transformation, industrial
  • World market: 1.6 TW space heating; 0.3 TW hot water; 1.3 TW process heat (solar crop drying: ” 0.05 TW)
  • Temporal mismatch between source and demand requires storage
  • (DS) yields high heat production costs: ($0.03-$0.20)/kW-hr
  • High-T solar thermal: currently lowest cost solar electric source ($0.12-0.18/kW-hr); potential to be competitive with fossil energy in long term, but needs large areas in sunbelt
  • Solar-to-electric efficiency 18-20% (research in thermochemical fuels: hydrogen, syn gas, metals)
Solar Land Area Requirements
Figure 4: Solar Land Requirements: 6 boxes at 3.3 TWatts Each (Source: Powering the Planet, Lewis et al.)

U.S. Land Area: 9.1×1012 m2 (incl. Alaska)

  • Average Insolation: 200 W/m2
  • 2000 U.S. Primary Power Consumption: 99 Quads=3.3 TW
  • 1999 U.S. Electricity Consumption = 0.4 TW
  •  3.3×1012 W/(2×102 W/m2 x 10% Efficiency) = 1.6×1011 m2 Requires 1.6×1011 m2/ 9.1×1012 m2 = 1.7% of Land

Solar Energy Utilization

The energy from the sun is

Solar energy utilization requires:

  1. solar capture and conversion and
  2. solar storage


Solar capture and conversion may be accomplished by photovoltaics (PVs). The challenge here is to dramatically reduce the cost per W of delivered solar electricity. Compared with fossil energy, solar energy is diffuse, and hence materials costs must be very inexpensive to make a solar-based process economical. Knowing the insolation striking an area of the earth for a 30-yr period, it is relatively simple to calculate the sale price of the converted energy that is needed to pay back at least the initial cost that is required to cover that area with the solar energy conversion system.

At 10% efficiency, and a cost of $300 m2 , both typical of current Si-based solar electricity modules, along with a balance of systems cost of $3 Wp (peak W), an electricity price of $0.35/kW-hr is required to cover the initial system costs. By comparison, fossil-derived electricity (high-value energy) now costs approximately $0.02–0.05 /kW-hr, and that cost includes storage and distribution costs. To reach a cost point near that of fossil-derived energy will thus require improvements in efficiency but additionally will require large decreases in cost, into a range below $100 /square meter.

For comparison, the cost of paint is about $1 /square meter, so the solar energy conversion system can cost 10 times more than the cost of paint, but not much more if it is to provide cost-effective primary energy.
In the absence of cost-effective storage, solar electricity can never be a primary energy source for society, because of the diurnal variation in local insolation. In principle, storage of electricity could be obtained using batteries, but at present no battery is inexpensive enough, when amortized over the 30-yr lifetime of a solar device, to satisfy the needed cost per W targets for the whole system. A second method is to store the electrical energy mechanically. For instance, electricity could be used to drive turbines to pump water uphill. This approach is relatively inexpensive for storing large amounts of energy at modest charge and discharge rates, but is not
well matched to being charged and discharged every 24 h to compensate for the diurnal cycle. For example, buffering the daynight cycle in the U.S. energy demand by this approach would require a pumping capacity equivalent of 5,000 Hoover Dams, filling and emptying reservoirs every day and every night.

2. Solar Thermal 

Currently, the cheapest method of solar energy capture, conversion, and storage is solar thermal technology, which can cost as little as $0.10–0.15 per kW-hr for electricity production. Advances in this potentially very important approach to solar energy utilization will require new materials for the focusing and thermal capture of the energy in sunlight, as well as new thermochemical cycles for producing useful fuel from the captured solar energy. The possibility of integrated capture, conversion, and storage functions makes solar thermal technology an option that should be vigorously pursued to exploit the large untapped solar energy resource for carbon-neutral energy production.

3. Artificial Photosynthesis

A third method of storage is to borrow the design of nature, in which chemical bonds are broken and formed to produce solar fuels in an artificial photosynthesis process. Photosynthesis itself is relatively inefficient, when measured on a yearly average basis per unit area of insolation. For example, switchgrass, one of the fastest-growing crops, yields energy stored in biomass at a yearly averaged rate of 1 W/square meter. Because the averaged insolation at a typical midlatitude is 200–300 W/square meter, the yearly averaged energy conversion and storage efficiency of the most rapidly growing large area crops is currently 0.5%. Even if this efficiency could be reached with no energy inputs into the farm or any energy losses due to outputs from the utilization of thebiomass, growth of energy crops on all of the naturally irrigated cultivatable land on earth that is not currently used
for food crops would yield perhaps 5–10 TW of total power. Whereas biofuels derived from existing plants could provide a potentially significant contribution to liquid fuels for transportation uses (if cellulosic conversion technology can be successfully developed and deployed economically) increased energy conversion and storage efficiency are highly desirable to remove land area as a serious constraint on the amount of energy that can be obtained from the sun and stored in chemical bonds.

One approach is to develop an artificial photosynthetic process with an average efficiency significantly higher than plants or algae. The primary steps of photosynthesis
involve the conversion of sunlight into a ‘‘wireless current.’’ In all cases, to form a useful fuel, O2 must be evolved, so it can be released into our oxygen-containing atmosphere and used elsewhere as an oxidation reagent for fuel consumption. The reduced fuel could be either hydrogen from water reduction, or it could be an organic species, such as methanol or methane, that is derived from the fixation of atmospheric CO2. Recombination of the reduced fuel with released O2 would then regenerate the original species, closing the cycle in a carbon-neutral fashion. In natural photosynthesis, the anodic charge of the wireless current is used at the oxygen-evolving complex to oxidize water to oxygen, with the concomitant release of four protons. The cathodic charge of the wireless current is captured by Photosystem I to reduce the protons to ‘‘hydrogen,’’ with the reduced hydrogen equivalents stored through the conversion of NADP to NADPH. Thus, the overall primary events of photosynthesis store sunlight by the rearrangement of the chemical bonds of water, to form oxygen and Nature’s form of

An artificial photosynthetic system could be realized by spatially separating solid-state or molecular water reduction and oxidation catalysts and connecting them to a light collection and charge separation system. In one such construct, the spatially separated electron–hole pairs provided by a photovoltaic assembly based on a solid-state junction, on either the macroscale or the nanoscale, are captured by the catalysts, and the energy is stored in the bond rearrangement of water to H2 and O2.

Other concepts involve more intimate integration of the charge separation and chemical bond-forming functions, to avoid costs and system constraints associated with electrical contacts, wires, inverters, etc., involved with converting 1-eV photons into 1-eV chemical bonds through electricity as a discrete intermediary. One approach to this type of system is depicted in Fig. 1, in which the tightly integrated system is modeled after natural photosynthesis and serves as a model for the artificial photosynthetic systems that are discussed below.

(Source: Lewis et al, Powering the planet: Chemical challenges in solar energy utilization, 2006)

The Basic Science Needs for PVs 

One of the key issues in solar capture and conversion is how to separate charge efficiently over macroscopic distances without using expensive, highly pure, semiconductor materials. This effort requires the development of new chemical and materials methods to make polycrystalline and nanocrystalline semiconductors perform as if they were expensive single crystals. Numerous research approaches are being pursued. Materials consisting of a network of interpenetrating regions can facilitate effective charge separation and collection, thus relaxing the usual constraint in which the photogenerated carriers must exist long enough to traverse the entire distance of the cell. Present photon conversion devices based on a single-bandgap absorber, including semiconductor PV, have a theoretical thermodynamic conversion efficiency of 32% in unconcentrated sunlight. However, the conversion efficiency can be increased, in principle, to 45–65% if carrier thermalization can be prevented (by overcoming the so-called Shockley–Queisser limit). Multiple-bandgap absorbers in a cascaded junction configuration can result in high photoconversion efficiencies, particularly when cells are designed to sustain the operating conditions (e.g., elevated temperatures) associated with highly concentrated sunlight. It is expected that mature high concentration PV systems can provide 10–20% more energy than standard PV systems with the same installed power rating.

In addition to making evolutionary changes to existing PV technologies, new materials for next-generation PVs are needed. Building upon the recent success in developing efficient molecular organic PVs and the recent advances in the controlled assembly of hybrid organicinorganic nanostructures, organic and hybrid PV cells could possibly exceed 10% energy conversion efficiency, while offering a potentially inexpensive manufacturing paradigm (e.g., casting from emulsions, printing, and use of flexible substrates for production of large-area thin-film cells; ref. 14). To guide the PV nanostructure assembly, biologically derived andor genetically engineered systems might be used to control the crystal structure, phase, orientation, and nanostructural regularity of inorganic materials. Genetically modified photosynthetic complexes from plants and bacteria can also convert incident light into photocurrent. Although the present energy conversion efficiencies of such systems are low, the projected maximum could be possibly as high as 10%. Finally, the Shockley–Queisser limit may be overcome by using multilayer junctions of semiconductor quantum dots, quantum wells and related nanostructures, and new inorganic materials and photo assemblies. Such materials could channel the excess energy of electron hole pairs into photovoltages and photocurrents, with the design guided by a refined detailed understanding of photon absorption, charge creation, and charge separation processes.

(Source: Lewis et al, Powering the planet: Chemical challenges in solar energy utilization, 2006)