Depletion of fossil fuels and anthropogenic climate change—A review
Highlights
► Review of the development of emission scenarios. ► Survey of future fossil fuel trajectories used by the IPCC emission scenarios. ► Discussions on energy transitions in the light of oil depletion. ► Review of earlier studies of future climate change and fossil fuel limitations.
Introduction
Mankind's energy production is the principal contributor to mankind's release of greenhouse gases (GHG), in particular CO2, to the atmosphere with fossil fuel combustion as the key factor. As a result, anthropogenic GHG emissions and human-induced global warming are fundamentally linked to future energy production. Projections of how the global energy system will develop over the next century are cornerstones in the assessment of future climate change caused by mankind.
The Intergovernmental Panel on Climate Change (IPCC) and many others use climate models that rely on various emission scenarios to depict possible trajectories for future fossil fuel production and their correlating release of CO2. The Special Report on Emission Scenarios (SRES) (the current set of emission scenarios) was published by the IPCC in 2000 and remains an integral part of climate change modeling, as it has been used by the last IPCC reports (IPCC, 2001, IPCC, 2007).
As of 2010, world oil production remains around 85 million barrels per day (Mb/d) or 3900 million tons of oil equivalents (Mtoe) annually, with coal and natural gas at 3700 corresponding to 2900 Mtoe per year (BP, 2012). Some scenarios foresee a tenfold increase in world gas production, while others depict future oil production to reach 300 Mb/d by 2100. For example, 16 of the 40 coal scenarios contained in SRES simply grow exponentially until the year 2100 (Patzek and Croft, 2010). Emission scenarios also contain assumptions about future prices, technological developments and many other details related to fossil energy exploitation.
This article reviews the emission scenarios witnessed throughout history, their underlying assumptions on resource availability and future production expectations. Future scenarios with high emissions of CO2 also display significant increases in world production of oil, natural gas and coal. Can such assumptions remain justified in the light of the growing body of evidence suggesting that depletion of the world fossil energy resources, primarily oil, is a growing problem? In addition, published critique raised against the fossil fuel projections used by the IPCC is reviewed. Finally, this study compiles recent studies on how fossil fuel constraints may impact anthropogenic climate changes.
The Swedish Nobel prize laureate Arrhenius (1896) was among the first to theorize about the impact of CO2 on the earth's climate. However, these ideas were initially met with criticism and fell into obscurity until around the 1950s. Growing concern about mankind's increasing impact on the environment and refined analytical methods revitalized the issue of greenhouse gases after the 1950s. Separate threads of research were pursued by isolated groups of scientists, although an increasing number of studies pointed towards a connection between global warming and anthropogenic emissions of greenhouse gases (Peterson et al., 2008). Mainstream media and politicians largely ignored these results and only expressed concern over these findings much later.
In the 1980s, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) began to investigate the role of carbon dioxide and other emissions. Their interest leads to the establishment of the IPCC in 1988. This new organization became responsible for assessing scientific, technical and socio-economic information relevant for understanding mankind's role in climate change. Their synthesized results have been published in several assessments and special reports over the years (IPCC, 1990, IPCC, 1995, IPCC, 2001, IPCC, 2007). However, these findings are also largely dependent upon a set of assumed trajectories for future fossil fuel production and related emissions.
Various future pathways for society, its energy system and the associated release of greenhouse gases are a cornerstone in the estimation of future climate change. Such outlooks are commonly referred to as emission scenarios and are being used as input into climate models that transform the projected emissions into climatic changes. The IPCC has used a number of emission scenarios throughout its work. The first set was published in 1990, followed by subsequent publications in 1992 and the latest version from 2000. Titles, methods, classifications, assumptions have all changed over time and Girod et al. (2009) reviewed this in more detail.
The 1995 IPCC review of the old emission scenarios recommended that the full range of scenarios should be used as an input rather than just a single scenario. The conclusion was that there was no objective basis on which to assign likelihood to any of the scenarios (SRES, 2000). Meanwhile, a number of other weaknesses were also identified, such as the limited range of carbon intensities, the absence of a scenario with economic closure in the income gap between industrial and developing countries (SRES, 2000), or how the rapid growth in sulfur emissions did not reflect regional and local air quality concerns that might prompt limits on the future release of sulfur into the atmosphere (Grübler, 1998).
In addition, it was found that all scenarios from 1992 exaggerated recent trends for climate and economic development, leading to correspondingly exaggerated atmospheric GHG concentrations (Gray, 1998). In 1996, the IPCC chose to develop new scenarios and initiated the painstaking process of developing a new set for utilization in future climate change assessments (Nakićenović et al., 1998). This resulted in the current emission scenario set – often known as the Special Report on Emission Scenarios (SRES) – being published in 2000. This report forms the foundation of most recent long-term climate change projections, including those of the Fourth Assessment Report (IPCC, 2007).
The SRES writing teams outlined four different narratives to be used as storylines for the future. Six modeling teams (Table 1) generated quantifications of the narratives that laid the foundation of the 40 different scenarios contained in SRES. The scenarios can be divided into four families, each exploring different variants of global and regional development and their implications for global greenhouse gas emission. SRES storyline titles are simply named A1, A2, B1, and B2. They are characterized by global-regional focus and economic–environmental orientation and can be placed in a two-dimensional figure (Fig. 1). No scenario should be considered as a “business-as-usual”, even though the A1 family is often used as an example of how continued global focus on economic growth might evolve. It is also imperative to emphasize that none of the scenarios contain additional climate initiatives such as GHG reduction schemes or adaptations to the expected climate change. No disaster scenarios were considered and possible surprises, such as new world wars or economic downturns, were also disregarded. Hjerpe and Linnér (2008) described this as utopian thought with built-in linear logic.
The future is described as significantly wealthier than the current world in each of the four main narratives and their corresponding scenario families. There has been a significant discussion around the use of Market Exchange Rates (MER) or Purchasing Power Parity (PPP) as it can lead to significant economic differences in the long time scales used. For example, McKibbin et al. (2007) quantifies that MER terms can result in more than 40% higher emission projections compared with using PPP figures. Castles and Henderson (2003), Tol (2006), and van Vuuren and O'Neill (2006) expand further on this topic.
Van Ruijven et al. (2008) confer the actual models and their underlying concepts. The simplified substitution-based concept known as the “energy ladder” is applied consistently, and so is also the environmental Kuznetz curve (a U-shaped relation between economic development and environmental impact). However, van Ruijven et al. (2008) also acknowledge that SRES relies on limited amount of socioeconomic and energy data when only depicting the world in four large regions, i.e. OECD90, Asia, Africa+Latin America, and the so called REF-region consisting of countries undergoing economic reform. With more regions and improved data, it is likely that the dynamics of real world development could be more accurately captured.
All scenarios belonging to the same family were qualitative and quantitative adjusted to match the features of the narrative storyline. Overall, harmonization of 26 scenarios made them share assumptions for global population and gross domestic product (GDP) growth (SRES, 2000, Sivertsson, 2004). Although the scenarios share a few basic assumptions, they can differ substantially in other aspects, such as availability of fossil-fuel resources, resulting GHG emissions, the rate of energy-efficiency improvements, and the extent of renewable energy development.
The remaining 14 scenarios are different versions of the narratives with alternate assumptions for economic and population growth projections. These variations reflect the modeling teams' choice as an alternative to the harmonized scenarios. Marker scenarios are another form of scenario, which is considered by the SRES writing team to be the most illustrative scenario of a particular storyline. SRES (2000) and Höök et al. (2010a) contains more detailed descriptions of the scenario families, even though the main qualities of each storyline can be found in Table 2.
SRES (2000) presents 40 scenarios with different developments for the global energy system and the manmade greenhouse gas emissions. These scenarios are founded on literature reviews, development of emission narratives, and quantification of the narratives with the help of six integrated models from different countries. Four specific drivers for CO2 emissions, namely population; economic activity (gross domestic product or GDP) per capita; energy intensity (primary energy consumption per unit of GDP); and carbon intensity (CO2 emissions per unit of energy) are identified by the IPCC (Pielke et al., 2008). SRES illustrates that future emissions, even in the absence of any explicit environmental policies, very much depend on how economies and technologies are structured, the energy sources that are preferred and how people use available land area as well as the choices that people make.
IPCC claim that the scenarios “represent pertinent, plausible, alternative futures” and derive from a descriptive and open-ended methodology that aims to explore alternative futures (SRES, 2000). The emission scenarios are neither predictions nor forecasts, even though they are commonly used as such. In addition, no probabilities or likelihoods are assigned to any of scenarios since and all of them are considered equally plausible. This condition was a requirement made by the Terms of Reference (SRES, 2000).
The absence of likelihoods in SRES triggered critique (Schneider, 2001, Schneider, 2002, Webster et al., 2003) highlighting that decision-makers and policy analysts necessitate probability estimates to be able to assess the risks of climate change impacts resulting from these scenarios. The SRES team (Grübler and Nakićenović, 2001) countered by claiming that social systems (important in emission scenarios) are fundamentally different from natural science systems and are largely dependent on the choices people make.
Morgan and Keith (2008) reviewed available findings on scenario analyses and uncertainty and found that the “equal probability”-approach often lead to systematic overconfidence and bias. Jones (2001) concluded that equally valid scenarios cannot be realistic, since the range is due to a combination of component ranges of uncertainty, and thus the extremes of this range must be less probable than the central estimate. It has also been argued that the equal probability of each emission scenario is a rather odd postulation and even may be seen as an attempt to assign unjustifiably high weight to extreme outcomes (Höök et al., 2010a, Patzek and Croft, 2010). Clearly, the way uncertainty is handled and the suitability of assigning subjective probabilities to scenarios is a matter of lively debate and an important, but unresolved challenge in the application of climate scenarios (Dessai et al., 2007, Groves and Lempert, 2007, Schenk and Lensink, 2007, van Vuuren et al., 2008, Lemos and Rood, 2010).
Emissions scenarios serve as input to various climate models, where the latter depict how the climate may change under various assumptions for future anthropogenic emissions. From society's perspective, some outcomes are certainly more desirable than others. However, the equal probability assumption can act as a potential obstacle. Planners and engineers, who need to make decisions based on the impacts of climate change, must have a grasp of the inherent uncertainties in the guiding projections as well as the probabilities of the different outcomes. Walsh et al. (2004) and Green et al. (2009) provide additional discussion regarding this.
Section snippets
Fossil fuels in the global energy system
Since the dawn of the industrial revolution, fossil fuels have been the driving force behind the industrialized world and its economic growth. Fossil energy has grown from insignificant levels in 1800 to an annual output of nearly 10,000 million tons of oil equivalents (Fig. 2). At present, about 80% of all primary energy in the world is derived from fossil fuels with oil accounting for 32.8%, coal for 27.2% and natural gas for 20.9% (IEA, 2011). Combustible biomass and waste (10.2%), nuclear
Fossil fuel projections in SRES
Fossil fuels are the dominating GHG source and, consequently, assumed availability and future production paths are vital for projecting manmade changes to atmospheric concentration of CO2 and climate. However, the underlying assumptions and data sources in SRES (2000) are old or even outdated. This has to do with the one-sided view on fossil fuel availability expressed by the works that SRES relies on, chiefly relying on economic models rather than geological and technical estimates (Höök et
The complexity of energy substitutions
Anthropogenic climate change is an intricate problem arising from complex interactions between three distinct parameters—energy, economics, and environment. Energy is essential for economic growth and the development of society, but also a major factor for mankind's emission of GHGs. The core of the poodle is the realization that these three threads are not separate questions, but rather a single issue that necessitates a holistic treatment. The current stance with energy generally seen as an
Climate impact assessments from fossil fuel constraints
Fossil fuel depletion limits the maximum extent of anthropogenic global warming, although this is challenging to handle in a holistic manner. Energy constraints pose a threat to the economy (Nel and Cooper, 2009), and similarly changes in human energy-related behaviors can lead to a broad range of effects on natural ecosystems (Czúsz et al., 2010). Energy, economy and ecology are seldom seen as three interconnected problems. The lack of widely accepted benchmarks for energy constraints in
Concluding discussions
This far, peak oil and related limits to future fossil energy extraction are nearly absent in the climate change debate (Kharecha and Hansen, 2008). It is certainly about time to change this and stop seeing anthropogenic release of CO2 as something detached from future energy supply questions. Energy cannot be seen as a limitless input to economic/climate models and remain disconnected from the physical and logistical realities of supply (Nel and Cooper, 2009).
Vernon et al. (2011) found that
Acknowledgments
We would like to thank Dr Herbert West for providing valuable inspiration. Anders Sivertsson also has our sincerest gratitude for compiling useful material.
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