Monday, December 31, 2012

Scenarios and Forecasts of CO2 Emissions

Today's installment. This is another four papers, marked in bold the first time they appear. I can see already that either I am going to have to cut the number of papers covered or we are going to have to go to two volumes, which is an option. Also, I gave up and actually included an IPCC report in my list.


Economists first addressed the issue of climate change as part of the wave of interest in energy and environmental economics that followed the oil price shock in 1973-4. The first journal article on the issue is d’Arge et al. (1982), which references an earlier report (d’Arge et al., 1975) and conference paper by the authors.

Early scenarios and projections for future emissions of carbon dioxide were published the following year (Nordhaus and Yohe, 1983; Ausubel and Nordhaus, 1983; Edmonds and Reilly 1983). Edmonds and Reilly’s model was the basis of the energy module of the later IS92 scenarios. It consists of a multiregional supply and demand model for seven primary and secondary energy carriers. Aggregate energy demand is determined by GNP, which is driven by exogenous technological change, and autonomous energy efficiency improvements for each fuel type. There is also a feedback from energy prices to GNP. Predicted carbon emissions rose to 6.9 billion tonnes in 2000, 12.3 billion in 2025 and 26 billion by 2050 with an increasing share of emissions in the non-OECD world. The near-term prediction was remarkably accurate - actual global emissions were 6.8 billion tonnes in 2000. Predicted emissions for 2050 are higher than current BAU projections as we will see below. Carbon dioxide concentrations were predicted to double between 2049 and 2067 relative to the preindustrial level, which is in line with current BAU projections.

Many of the most important studies of future emissions have been published as reports of the Intergovernmental Panel on Climate Change (IPCC) and other agencies. The IPCC has commissioned emissions scenarios roughly every decade – the IS92 scenarios (Leggett et al., 1992), SRES scenarios (Nakicenovic et al., 2000), and RCP scenarios (van Vuuren et al., 2011).

The first IPCC scenarios were produced in 1989. Due to the ending of communism in the USSR and Eastern Europe, the signing of an international agreement on the control of CFCs and new information in various input variables, the IPCC requested a revision only two years later (Leggett et al., 1992). These new scenarios were inputs to the 1992 Supplementary Report and the 1995 Second Assessment Report. These were the first scenarios to include the full suite of greenhouse gases as well as sulphur emissions (Nakicenovic, 2000). In addition to the energy module described above there are deforestation, agriculture, and halocarbon emission modules. Control of sulphur emissions is modelled as an increasing function of income level and an atmosphere/ocean module translates emissions into climate change. The scenarios modelled six alternative future worlds and comprehensively covered all sources of greenhouse gases translating them into CO2 equivalents. Scenarios varied on assumed population and economic growth and the availability of alternative energy technologies and fossil fuel resources. These scenarios result in a very broad range of emissions trajectories. IS92e saw emissions rising to the 20 GT range around 2050 and the 35 GT by 2100. IS92c predicted that emissions would decline after 2020. The preferred scenario, IS92a, was midway between these extremes with emissions around 20 GT in 2100.

The SRES scenarios prepared for the Third Assessment Report (Nakicenovic et al., 2000) are perhaps the best known of the IPCC scenarios. Nakicenovic (2000) discusses the development of these scenarios. Four storylines were developed which vary by population and economic growth, degree of international cooperation and trade, the rate of technological development, and the types of future policies. Five integrated assessment modeling groups cooperated to develop a total of forty scenarios based on the storylines. The results from one of the modeling groups was considered the representative or “marker” scenario of the storyline. The ensemble of results portray greater radiative forcing than the IS92 scenarios mainly because of reduced forecasts of sulfur emissions. The marker A1 and A2 scenarios also project less carbon emissions in 2050 than Edmonds and Reilly (1983).

van Vuuren et al., (2011) introduce the latest IPCC scenarios known as the Representative Concentration Pathways (RCP) prepared for the Fifth Assessment Report. This process is the reverse of previous scenario-building exercises as it starts with concentration pathways based on given radiative forcing targets and then works back to socio-economic scenarios that could lead to those outcomes. These pathways were supposed to be representative of the range of scenarios in the literature and are named for the level of radiative forcing in Watts per square metre in 2100. The RCP 8.5 and 6.0 scenarios might be seen as business as usual under more or less optimistic assumptions about technological change while the RCP 4.5 and 2.6 scenarios assume policy to control emissions. The RCP 2.6 scenario results in negative emissions in the second half of the 21st century which is only possible with biomass carbon capture and storage or air capture of carbon dioxide. Emissions under the RCP 8.5 scenario track those in Edmonds and Reilly (1983) while they are lower in the other scenarios.


Ausubel, J. H. & W. D. Nordhaus (1983) A review of estimates of future carbon dioxide emissions, in T. F. Malone (ed.) Changing Climate: Report of the Carbon Dioxide Assessment Committee, National Academy Press, Washington DC. Chapter 2.2 pp153-185.

  d’Arge, R. C. et al. (1975) Economic and Social Measures of Biologic and Climatic Change, U.S. Department of Transportation.

d'Arge, Ralph C., William D. Schulze, and David S. Brookshire (1982) Carbon dioxide and intergenerational choice, American Economic Review 72(2): 251-256.

Edmonds, Jae and John Reilly (1983) Global energy and CO2 to the year 2050, The Energy Journal 4(3): 21-48. 

Leggett, J., W. J. Pepper, and R. J. Swart (1992) Emissions scenarios for the IPCC: an update, in: J. T. Houghton, B. A. Callander, and S. K. Varney (eds.) Climate Change 1992: The Supplementary Report to the IPCC Scientific Assessment, Cambridge University Press. Chapter A3, 69-96. 

Nakićenović, Nebojša (2000) Greenhouse gas emissions scenarios, Technological Forecasting and Social Change 65(2): 149–166.

Nakicenovic, Nebojsa et al. (2000) Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change, Cambridge University Press.

Nordhaus, W. D. and G. W. Yohe (1983) Future paths of energy and carbon dioxide emissions, in T. F. Malone (ed.) Changing Climate: Report of the Carbon Dioxide Assessment Committee, National Academy Press, Washington DC. Chapter 2.1, pp87-152. 

van Vuuren, Detlef P., Jae Edmonds, Mikiko Kainuma, Keywan Riahi, Allison Thomson, Kathy Hibbard, George C. Hurtt, Tom Kram, Volker Krey, Jean-Francois Lamarque, Toshihiko Masui, Malte Meinshausen, Nebojsa Nakicenovic, Steven J. Smith, and Steven K. Rose (2011) The representative concentration pathways: an overview, Climatic Change 109(1-2): 5-31.  

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