Changing the

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Certainly for children, and for many (perhaps most) in their adulthood, the notion of human alteration of the atmosphere is baffling. The blue canopy is rarely conceived in human scale. Rather, it most often inspires the poesy of the human mind and spirit, in which we celebrate and bow in deference to the heavens and their celestial rulers. A distinct trait of modernity is that we now engage the heavens as a project of science and economics. We may have little choice, as we have changed its chemistry and the mechanics

3 Data from UN and US sources indicate that urban communities account for more than three quarters of global CO2 emissions, despite containing less than one half of the human population. The wealthy urban communities of North America, Europe, Japan, Australia and New Zealand release over 40% of the world's annual CO2 emissions, although they are home to only 13% of the human community. By contrast, most of rural life is sustenance based and releases carbon at very modest rates - its population share of 54% accounts for less than 30% of yearly anthropocentric emissions (UN 2004; EI A 2004).

Table 2.1. Summary of IPCC scenarios.






Scenario group







Population in 2050 and 2100 (Billion)













World GDP in 2050 and 2100 (Trillion 1990 US$)













Share of zero carbon in primary energy in 2100 (%)







Cumulative carbon emissions from fossil fuels (1990-2100, GtC)







Cumulative carbon emissions from land use change (1990-2100, GtC)







Carbon concentration in 2100 (ppm)







Mean temperature increase in 2100 compared to







of climate associated with the molecular composition of the sky (for a discussion of this paradox, see Byrne and Glover 2005).

Future CO2 concentrations in the atmosphere are partly a function of the amount of CO2 released from fossil fuels and land use change over time. The US Energy Information Administration (EIA 2006, 2007) provides projections of world, regional and national CO2 emissions from the use of fossil fuels for the next 25 years (2006-2030). The IPCC has produced 40 pathways, grouped within four sets of scenarios referred to as 'families', to capture the range of physical impacts associated with alternative assumptions about global social and economic trends. These families in turn have been grouped under the headings A1, A2, B1 and B2 (see Table 2.1).

The A1 scenario family describes a future with rapid economic growth and global population that peaks in mid-century and declines thereafter. Its subgroups map changes in the world energy system - a fossil intensive path (A1FI), a path with increasing reliance on non-fossil energy sources (A1T), or a path with a mix of fossil and non-fossil sources (A1B). Under the A2 scenario family, economic growth is regionally concentrated among Southern4 nations and population is continuously increasing. The B1 scenario family describes a world with rapid change in economic structures, toward a service and information economy and with the same population trends as in the A1 scenario. The B2 scenario family emphasizes local solutions for economic, social and environmental sustainability, where global population continually increases but at a rate lower than trends in A2. In B2, intermediate levels of economic development coincide with less rapid and more diverse technological change than in the A1 and B1 storylines (IPCC 2001).

4 'South' and 'Southern' are used here to refer to the countries of Latin America, Africa, and Asia (excepting Japan, Australia and New Zealand), which are characterized by comparatively low annual CO2 emissions per capita.






Fig. 2.1. Projected global share of industrialized countries' CO2 emissions from fossil fuel burning under a BAU scenario (%).

Among these scenarios, A1B represents a mid-range path which can be considered a business as usual; (BAU) scenario for future CO2 emissions.5 After combining the EIA's reference case projections of fossil fuel-based CO2 emissions for 2006-2030 and the IPCC's A1B projections for 2031-2100, BAU projections are made for future world CO2 emissions from fossil fuels. These results were then combined with the IPCC's projections for emissions related to land use change for 2006-2100, under the A1B scenario.

An important aspect of future CO2 emissions involves the location of these emissions. Currently, most fossil fuel-based CO2 emissions originate in industrialized countries. However, rapid economic development and high population growth are expected to significantly increase the share of such emissions attributed to Southern countries. Nevertheless, on a per capita basis, emissions from industrialized countries are likely to remain higher for some time. Projections by the EIA provide the total fossil fuel-based CO2 emissions of the industrialized (Annex 1) and industrializing (non-Annex 1) countries for 2006-2030 (EIA, 2006). A statistical curve fitting of EIA projections for the two groups indicates industrialized countries will account for a slowly declining global share of fossil fuel emissions (see Fig. 2.1). For the period 2031-2100, CO2 emissions among industrialized and industrializing countries are derived by assuming the same trend for change in the national shares of emissions as we found during 2006-2030. This assumption means that the projected share of fossil fuel-based CO2 emissions from Annex 1 will decrease from 51% in 2010 to 17% in 2100. The resulting BAU emission scenario (expressed in total CO2 emissions and per capita emissions) is presented in Figs. 2.2 and 2.3, respectively.

Researchers at the Center for Energy and Environmental Policy (CEEP) have investigated scenarios for large CO2 emission reductions since the early 1990s. A 1998 publication sought to fix scenario parameters in a manner that would satisfy: (1) a sustainability condition based on IPCC assessments of needed global CO2 emission cuts to halt warming risk at

5 For example, if we average carbon concentration levels and mean temperature increases under the scenarios in Table 2.1, the average value will be 710 ppm and the temperature increase will be 3°C, which are the concentration level and temperature increase for the A1B scenario.

Projection based on IPCC A1B

Global concentration 700 ppm

70 6050 40302010 0

1950 1975 2000 2025 2050 2075 2100 Fig. 2.2. CO2 Emissions from fossil fuel burning under a BAU scenario (in GtCO2).

Projection based on IPCC A1B

Global concentration 700 ppm

Bau Scenario
Fig. 2.3. Per capita CO2 emissions from fossil fuel burning under a BAU scenario (tCO2 per capita).

current levels; and (2) an equity principle in which the biospheric carbon store is equally shared (Byrne et al. 1998). The sustainability condition used in the modelling reported here is a level of emissions that will not increase carbon concentrations above 450 ppm by 2050.6 This agrees with the most recent IPCC assessment (2007). To determine this pathway, the interrelation of carbon concentration levels and emissions are first established, and then a corresponding emissions path is derived. For this purpose, CEEP researchers relied upon

6The recent report of the UNDP (2007) on human development uses a 450ppm concentration as well.

Fig. 2.4. CO2 emissions from fossil fuel burning in Annex 1 countries under the BAU and CEEP scenarios (in GtCO2).

a mixed-layer, pulse response function model (known as the Bern model).7 In addition, assumptions were made regarding carbon uptake from the land biosphere and GHG emissions due to land use change based on IPCC (2001) and Joos et al. (2001).8

To satisfy the model's equity principle, a projection of future population growth is built on United Nations population projections through 2050 (UN, 2005)' afterward, it is assumed that human population would stabilize at the 2050 level. Finally, an emissions path must stipulate reductions in carbon emissions by industrialized and industrializing countries. Starting in 2010, Annex 1 emissions are modelled to decline rapidly in order to reach a 2050 rate consistent with the specified sustainability and equity requirements. For Southern countries, carbon emissions are modelled to increase through 2040 and then decline, but at rates which are always slower than those for Annex 1.

Specifically, for Annex 1 countries, emissions would follow the BAU scenario until 2010 and subsequently decline to a level of 2 tCO2 per person by 2050 (see Fig. 2.4). Total emissions from Annex 1 countries in 2100 would equal 2.6 GtCO2. For non-Annex 1 countries, emissions would follow the BAU scenario until 2025, after which they grow slower than the BAU case. After 2040, non-Annex 1 emissions begin to decline, reaching the level of 2 tCO2 per person in 2060 (see Fig. 2.5).9 This scenario (hereinafter called the CEEP scenario)

7The model was developed by the Climate and Environmental Physics Institute at the University of Bern, Switzerland. Detailed discussion of this model, due to its technical complexity, is beyond the scope of this chapter. Readers can consult the IPCC's discussion of the model (1997); see also Joos and Bruno (1996) and Joos et al. (1996).

8Specifically, we used the assumption in the A1B scenario of emissions from land use change equal to 0.4 PgC per year, which implies that excess carbon released from the land biosphere is 2.7 PgC (based on Joos et al. 2001).

9The level of 2 tCO2 per person in 2100 is based on the sustainable and equity rate of 3.3 tCO2 per person at the 1990 world population level developed by Byrne et al. (1998). However, the 1998 Byrne et al. paper included all greenhouse gases that are not available for many countries, the analysis reported here addresses only CO2. As a result, estimates of atmospheric stability (i.e. 450 ppm of CO2) under the different scenarios presented in this chapter may understate the needed level of reductions.

Fig. 2.5. CO2 emissions from fossil fuel burning in non-Annex 1 countries under the BAU and CEEP scenarios (in GtCO2).
Fig. 2.6. CO2 emissions from fossil fuel burning under the CEEP scenario (in GtCO2).

expects Southern nations will take some time to adjust emission trends, while industrialized nations are subjected to an obligation of rapid emission reductions in order for the human community to meet the sustainability target.

In Figs. 2.6 and 2.7, resulting projections under the CEEP scenario are presented. Figure 2.6 shows that, for Annex 1 countries, per capita emissions should rapidly decline after 2010 to 2 tCO2 per person in 2050. For the non-Annex 1 countries, per capita emissions can grow until 2040, reaching 3.5 tCO2 per person and then declining to a global average of 2 tCO2 per person after 2060. Figure 2.7 indicates that, under the CEEP scenario, the achievement of a sustainable level of carbon concentration (i.e. 450 ppm by 2050) requires emissions to be nearly one third of those forecasted in the BAU scenario.

Actual data

CEEP scenario

Global concentration 450 ppm

1950 1975 2000 2025 2050 2075 2100

Fig. 2.7. Total CO2 emissions from fossil fuel burning under the CEEP scenario (in GtCO2).

1950 1975 2000 2025 2050 2075 2100

Fig. 2.7. Total CO2 emissions from fossil fuel burning under the CEEP scenario (in GtCO2).

750 700 650 600 550 500 450 400 350 300







Fig. 2.8. Projections of atmospheric carbon concentration under the BAU and CEEP scenarios (m ppm).

For comparison, the carbon concentration paths for the BAU and CEEP scenarios are presented in Fig. 2.8 . Under the BAU scenario, carbon concentrations will gradually increase and reach approximately 520 ppm in 2050 and 700 ppm in 2100. By contrast, under the CEEP scenario, concentrations stabilize around 450 ppm by 2050. Obviously, the BAU scenario violates the specified sustainability condition and equity principle.

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