IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group III: Mitigation of Climate Change

4.2.2 Emission trends of all GHGs

Growing global dependence on coal, oil and natural gas since the mid-19th century has led to the release of over 1100 GtCO2 into the atmosphere (IPCC, 2001). Global CO2 emissions from fuel combustion (around 70% of total GHG emissions and 80% of total CO2) temporarily stabilized after the two oil crises in 1973 and 1979 before growth continued (Figure 4.6). (Emission data can be found at UNFCCC, 2006 and EEA, 2005). Analyses of potential CO2 reductions for energy-supply options (for example IPCC, 2001; Sims et al., 2003a; IEA/NEA, 2005; IEA, 2006b) showed that emissions from the energy-supply sector have grown at over 1.5% per year from around 20 GtCO2 (5.5 GtC) in 1990 to over 26 GtCO2 (7 GtC) by 2005.


Figure 4.6: Global trends in carbon dioxide emissions from fuel combustion by region from 1971 to 2004.

Note: EECCA = countries of Eastern Europe, the Caucasus and Central Asia.

The European Union’s CO2 emissions almost stabilized in this period mainly due to reductions by Germany, Sweden, and UK, but offset by increases by other EU-15 members (BP, 2004) such that total CO2 emissions had risen 6.5% by 2004. Other OECD country emissions increased by 20% during the same period, Brazil by 68%, and Asia by 104%. From 1990 to 2005, China’s CO2 emissions increased from 676 to 1,491 MtCO2/yr to become 18.7% of global emissions (IEEJ, 2005; BP, 2006) second only to the US. Carbon emissions from non OECD Europe and the FSU dropped by 38% between 1989 and 1999 but have since started to increase as their economies rebound.

Natural gas and nuclear gained an increased market share after the oil crises in the 1970s and continue to play a role in lowering GHG emissions, along with renewable energy. Continuous technical progress towards non-carbon energy technologies and energy-efficiency improvements leads to an annual decline in carbon intensity. The carbon intensity of global primary energy use declined from 78 gCO2/MJ in 1973 to 61 gCO2/MJ in 2000 (BP, 2005) mainly due to diversification of energy supply away from oil. China’s carbon-intensity reduction was around 5%/yr during the period 1980 to 2000 with 3%/yr expected out to 2050 (Chen, 2005), although recent revision of China’s GDP growth for 2004 by government officials may affect this prediction. The US has decreased its GHG intensity (GHG/unit GDP) by 2% in 2003 and 2.5% in 2004 (Snow, 2006) although actual emissions rose.

For the power generation and heat supply sector, emissions were 12.7.GtCO2-eq in 2004 (26% of total) including 2.2 GtCO2-eq from methane (31% of total) and traces of N2O (Chapter 1). In 2030, according to the World Energy Outlook 2006 baseline (IEA, 2006b), these will have increased to 17.7 GtCO2-eq. During combustion of fossil fuels and biomass, nitrous oxide, as well as methane, is produced. Methane emissions from natural gas production, transmission and distribution are uncertain (UNFCCC, 2004). The losses to the atmosphere reported to the UNFCCC in 2002 were in the range 0.3–1.6% of the natural gas consumed. For more than a decade, emissions from flaring and venting of the gas associated with oil extraction have remained stable at about 0.3 GtCO2-eq/yr. Developing countries accounted for more than 85% of this emission source (GGFR, 2004).

Coal bed methane (CBM, Section is naturally contained in coal seams and adjacent rock strata. Unless it is intentionally drained and captured from the coal and rock the process of coal extraction will continue to liberate methane into the atmosphere. Around 10% of total anthropogenic methane emissions in the USA are from this source (US EPA, 2003). The 13 major coal-producing countries together produce 85% of worldwide CBM estimated to be 0.24 GtCO2-eq in 2000. China was the largest emitter (0.1 GtCO2-eq) followed by the USA (0.04 GtCO2-eq), and Ukraine (0.03 GtCO2-eq). Total CBM emissions are expected to exceed 0.3 GtCO2-eq in 2020 (US EPA, 2003) unless mitigation projects are implemented.

Other GHGs are produced by the energy sector but in relatively low volumes. SF6 is widely used in high-voltage gas-insulated substations, switches and circuit breakers because of its high di-electric constant and electrical insulating properties (Section 7.4.8). Its 100-year global warming potential (GWP) is 23,900 times that of CO2 and it has a natural lifetime in the atmosphere of 3200 years, making it among the most potent of heat-trapping gases. Approximately 80% of SF6 sales go to power utilities and electric power equipment manufacturers. The US government formed a partnership with 62 electric power generators and utilities (being about 35% of the USA power grid) to voluntarily reduce leakage of SF6 from electrical equipment and the release rate dropped from 17% of stocks to 9% between 1999 and 2002. This represented a 10% reduction from the 1999 baseline to 0.014 GtCO2-eq (EPA, 2003). Australia and the Netherlands also have programmes to reduce SF6 emissions and a voluntary agreement in Norway should lead to 13% reductions by 2005 and 30% by 2010 below their 2000 release rates. CFC-114 is used as a coolant in gaseous diffusion enrichment for nuclear power, but its GHG contribution is small compared to CO2 emissions (Dones et al., 2005).