1991). The approach begins with an identity in which CO2 emissions from

fossil fuel combustion can be expressed as the product of four terms, as follows: $$ \textCO_1 = (\textCO_ 2/\textPE)\times (\textPE/\textGDP) \times (\textGDP/\textPOP) \times \textPOP $$where CO2 is CO2 emission, PE is primary energy consumption, GDP is gross domestic product, and POP is population. The term CO2/PE represents average carbon intensity of energy, PE/GDP represents economy-wide energy intensity, and GDP/POP represents average per capita GDP. Figure 9 shows the result of the decomposition. Fig. 9 Decomposition of global CO2 emissions change in the s600 scenario Population and per capita GDP are the increasing factors. Per capita GDP increases rapidly, reaching 2.4-fold the 2005 level by 2050. In spite of the increasing population and per capita GDP, CO2 emissions decrease because of significant

reductions of energy intensity and carbon intensity. Energy intensity is the fastest-declining Selleck CBL0137 factor in the coming 3 decades and halves by 2040. Carbon intensity plays a somewhat smaller role than energy intensity in reducing CO2 in the near future. As time passes, however, it plays an increasingly important role, eventually overtaking energy intensity after 2040. By 2050, carbon intensity drops to one-fourth selleck inhibitor of the 2005 level. Energy system transitions This section interprets sectoral results to help us better understand the energy system transitions in a scenario where the targeted 50 % reduction of GHG emissions by 2050 is achieved. Power generation In the reference

scenario, global power generation increases from 17 to 47 PWh over the period from 2005 to 2050 (Fig. 10). The energy source composition changes moderately in the reference scenario over the same period. The share of coal, for example, increases from 42 to 51 %. The CO2 emission factor of electricity, only namely, CO2 emission per unit of electricity generation, decreases gradually over time, thanks mainly to improved generation efficiency in thermal power plants. Fig. 10 Transition in the power generation sector. The CO2 emission factor of electricity denotes the CO2 emission per unit of electricity generation In contrast to the reference scenario, power generation technologies drastically change in the s600 scenario. Coal power generation, the largest contributor to CO2 emission in 2005, contributes progressively less in s600 as time passes, and CCS is introduced after 2020. The deployment of renewable energy accelerates over the same period: wind accelerates after 2010; solar and biomass accelerate after 2020 and 2030, respectively. Thus, the share of renewables dramatically increases over time: by 2050, wind, solar, biomass, and hydro together account for about 75 % of the total power generation.