The document discusses the constraints on future energy transitions given environmental impacts from past transitions. It notes that past transitions from wood to coal had minimal global environmental impacts due to smaller human populations and less powerful technologies, but future transitions must consider effects on climate change, air pollution, and biodiversity loss. It argues that environmental factors may drive the next transition as a key consideration, rather than just energy quality and cost factors. Sustainable energy sources will be needed to alleviate energy poverty and support development while respecting planetary boundaries.

1. Energy transitions: The environmental frontier is closed
The transition from wood to coal occurred when the human population was small, its affluence was
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modest, and its technologies were much less powerful than today. As a result, environmental impacts
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associated with energyhad negligible global impact, although local impacts were at times quite significant.
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Any future energy transition will operate under a new set of environmental constraints. Environmental
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change has significantly impaired the health of people, economics and ecosystems at local, regional and
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global scales. Future energy systems must be designed and deployed with environmental constraints that
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were absent from the minds of the inventors of the steam engine and internal combustion engines.
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Air pollution and climate change
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Atmospheric releases from fossil fuel energy systems comprise 64 percent of global anthropogenic
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carbon dioxide emissions from 1850-1990, 89 percent of global anthropogenic sulfur emissions from 1850
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to 1990, and 17 percent of global anthropogenic methane emissions from 1860-1994. Fossil energy
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combustion also releases significant quantities of nitrogen oxide; in the United States, 23 percent of such
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emissions are from energy use. Power generation using fossil fuels, especially coal, is a principal source of
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trace heavy metals such as mercury, selenium, and arsenic.
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These emissions drive a range of global and regional environmental changes, including global
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climate change, acid deposition, and urban smog, and they pose a major health risk. According to the Health
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Effects Institute, the global annual burden of outdoor air pollution amounts to about 0.8 million premature
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deaths and 6.4 million years of life lost. This burden occurs predominantly in developing countries; 65% in
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Asia alone. According to the World Health Organization, in the year 2000, indoor air pollution from solid
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fuel use was responsible for more than 1.6 million annual deaths and 2.7% of the global burden of disease.
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This makes this risk factor the second biggest environmental contributor to ill health, behind unsafe water
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and sanitation.
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Climate change may be the most far-reaching impact associated with fossil fuel use. According to
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the Intergovernmental Panel on Climate Change (IPCC), the global atmospheric concentration of carbon
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dioxide has increased from a pre-industrial value of about 280 parts per million (ppm) to 379 ppm in 2005
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(Figure 6). The atmospheric concentration of carbon dioxide in 2005 exceeds by far the natural range over
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the last 650,000 years(180 to 300 ppm) as determined from ice cores. The primary source of the increased
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atmospheric concentration of carbon dioxide since the pre-industrial period results from fossil fuel use,
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with land use change providinganother significant but smaller contribution. The increase in carbon dioxide
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concentrations are a principal driving force behind the observed increase in globally averaged
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temperatures since the mid-20th century.
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Carbon intensity is an increasingly important attribute of fuel and power systems. Social and
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political forces to address climate change may produce another distinguishing feature of the next energy
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transition: environmental considerations may be a key important driver, rather than the inherent
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advantages of energy systems as measured by energy density, power density, net energy, and so on.
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2. Appropriation of the products of the biosphere
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The low energy and power density of most
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renewable alternatives collides with a second global
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environmental imperative: human use of the Earth's
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plant life for food, fiber, wood and fuel wood. Satellite
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measurementshave been used to calculate the annual
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net primary production (NPP)—the net amount of
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solar energy converted to plant organic matter
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through photosynthesis—on land, and then combined
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with models to estimate the annual percentage of NPP
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humans consume (Figure 2). Humans in sparsely
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populated areas, like the Amazon, consume a very
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small percentage of locally generated NPP. Large urban areas consume 300 times more than the local area
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produced. North Americans use almost 24 percent of the region's NPP. On a global scale, humans annually
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require 20 percent of global NPP.
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Human appropriation of NPP, apart from leaving less for other species to use, alters the
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composition of the atmosphere, levels of biodiversity, energy flows within food webs, and the provision of
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important ecosystem services. There is strong evidence from the Millennium Ecosystem Assessment and
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other research that our use of NPP has seriously compromised many of the planet's basic ecosystem
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services. Replacing energy-dense liquid fuels from crude oil with less energy dense biomass fuels will
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require 1,000- to 10,000-fold increase in land area relative to the existing energy infrastructure, and thus
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place additional significant pressure on the planet's life support systems.
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The rise of energy markets
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When coal replaced wood, most energy
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markets were local or regional in scale, and
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many were informal. Energy prices were based
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on local economic and political forces. Most
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energy today is traded in formal markets,
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and prices often are influenced by global
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events. Crude oil prices drive the trends in
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price for most other forms of energy, and they
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are formed by a complex, dynamic, and often
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unpredictable array of economic, geologic,
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technological, weather, political, and strategic
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forces. The rise of commodity and futures
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markets for energy not only added volatility to
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energy markets, and hence energy prices, but
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also helped elevate energy as to a key strategic
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financial commodity (Figure 3). The sheer volume of energy bought and sold today combined with high
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energy prices has transformed energy corporations into powerful multinational forces. In 2006, five of the
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world's largest corporations were energy suppliers (Exxon Mobil, Royal Dutch Shell, BP, Chevron, and
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ConocoPhillips). The privatization of state-owned energy industries is also a development of historic
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dimensions that is transforming the global markets for oil, gas, coal and electric power.
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Global market forces will thus be an important driving force behind the next energy transition.
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There is considerable debate about the extent to which markets can and should be relied upon to guide the
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choice of our future energy mix. Externalities and subsidies are pervasive across all energy systems in
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Figure 3. The price of crude oil futures on the New York
Mercantile Exchange. (Source: WTRG Economics)
Figure 2. Human appropriation of net primary
production (NPP) as a percentage of the local NPP.
(Image retrieved from NASA)

3. every nation. The external cost of greenhouse gas emissions from energy use looms as a critical aspect of
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energy markets and environmental policy. The distortion of market signals by subsidies and externalities
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suggeststhat government policy intervention isneeded to produce the socially desirable mix of energy. The
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effort to regulate greenhouse gas emissions at the international level is the penultimate example of
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government intervention in energy markets. The political and social debate about the nature and degree of
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government energy policy will intensify when global crude oil supply visibly declines and as pressure
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mounts to act on climate change.
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Energy and poverty
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The energy transition that powered the
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Industrial Revolution helped create a new
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economic and social class by raising the
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incomes and changing the occupations of a large
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fraction of society who were then employed in
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rural, agrarian economies. The next energy
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transition will occur under fundamentally
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different socioeconomic conditions. Future
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energysystems must supplyadequate energy to
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support the high and still growing living
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standards in wealthy nations, and they must
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supply energy sufficient to relieve the abject
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poverty of the world's poorest. The scale of the world's underclass is unprecedented in human history.
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According to the World Bank, about 1.2 billion people still live on less than $1 per day, and almost 3
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billion on less than $2 per day. Nearly 110 million primary school age children are out of school, 60
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percent of them girls.31 million people are infected with HIV/AIDS. And many more live without adequate
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food, shelter, safe water, and sanitation.
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Energy use and economic development go hand-in-hand (Figure 4), so poverty has an important
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energy dimension: the lack of access to high quality forms of energy. Energy poverty has been defined
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as the absence of sufficient choice in accessing adequate, affordable, reliable, high quality, safe and
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environmentally benign energy services to support economic and human development. Nearly 1.6 billion
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people have no access to electricity and some 2.4 billion people rely on traditional biomass—wood,
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agricultural residues and dung—for cooking and heating. The combustion of those traditional fuels has
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profound human health impacts, especially for woman and children. Access to liquid and gaseous fuels and
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electricity is a necessary condition for poverty reduction and improvements in human health.
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Conclusions
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The debate about "peak oil" aside, there are relatively abundant remaining supplies of fossil fuels.
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Their quality is declining, but not yet to the extent that increasing scarcity will help trigger a major energy
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transition like wood scarcity did in the 19th century. The costs of wind, solar and biomass have declined
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due to steady technical advances, but in key areas of energy quality—density, net energy, intermittency,
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flexibility, and so on—they remain inferior to conventional fuels. Thus, alternative energy sources are not
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likely to supplant fossil fuels in the short term without substantial and concerted policy intervention. The
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need to restrain carbon emissions may provide the political and social pressure to accelerate the transition
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to wind, biomass and solar, as this is one area where they clearly trump fossil fuels. Electricity from wind
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and solar sources may face competition from nuclear power, the sole established low-carbon power source
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with significant potential for expansion. If concerns about climate change drive a transition to renewable
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sources, it will be the first time in human history that energetic imperatives, especially the economic
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advantages of higher-quality fuels, were not the principal impetus.
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Figure 4. Energy and basic human needs. The international
relationship between energy. (Source: UNDP, 2002; WRI, 2002)