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IPCC Fourth Assessment Report: Climate Change 2007 |
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Climate Change 2007: Working Group III: Mitigation of Climate Change 1.3 Energy, emissions and trends in Research and Development – are we on track? 1.3.1 Review of the last three decades Since pre-industrial times, increasing emissions of GHGs due to human activities have led to a marked increase in atmospheric concentrations of the long-lived GHG gases carbon dioxide (CO2), CH4, and nitrous oxide (N2O), perfluorocarbons PFCs, hydrofluorocarbons (HFCs) and sulphur hexafluoride (SF6) and ozone-depleting substances (ODS; chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons) and the human-induced radiative forcing of the Earth’s climate is largely due to the increases in these concentrations. The predominant sources of the increase in GHGs are from the combustion of fossil fuels. Atmospheric CO2 concentrations have increased by almost 100 ppm in comparison to its preindustrial levels, reaching 379 ppm in 2005, with mean annual growth rates in the 2000–2005 period that were higher than those in the 1990s. The direct effect of all the long-lived GHGs is substantial, with the total CO2 equivalent concentration of these gases currently being estimated to be around 455 ppm CO2-eq (range: 433–477 ppm CO2-eq). The effects of aerosol and land-use changes reduce radiative forcing so that the net forcing of human activities is in the range of 311 to 435 ppm CO2-eq, with a central estimate of about 375 ppm CO2-eq. A variety of sources exist for determining global and regional GHG and other climate forcing agent trends. Each source has its strengths and weaknesses and uncertainties. The EDGAR database (Olivier et al., 2005, 2006) contains global GHG emission trends categorized by broad sectors for the period 1970–2004, and Marland et al. (2006) report CO2 emissions on a global basis. Both databases show a similar temporal evolution of emissions. Since 1970, the global warming potential (GWP)-weighted emissions of GHGs (not including ODS which are controlled under the Montreal Protocol), have increased by approximately 70%, (24% since 1990), with CO2 being the largest source, having grown by approximately 80% (28% since 1990) to represent 77% of total anthropogenic emissions in 2004 (74% in 1990) (Figure 1.1). Radiative forcing as a result of increases in atmospheric CO2 concentrations caused by human activities since the preindustrial era predominates over all other radiative forcing agents (IPCC, 2007a, SPM). Total CH4 emissions have risen by about 40% from 1970 (11% from 1990), and on a sectoral basis there has been an 84% (12% from 1990) increase from combustion and the use of fossil fuels, while agricultural emissions have remained roughly stable due to compensating falls and increases in rice and livestock production, respectively. N2O emissions have grown by 50% since 1970 (11% since 1990), mainly due to the increased use of fertilizer and the aggregate growth of agriculture. Industrial process emissions of N2O have fallen during this period. The use and emissions of all fluorinated gases (including those controlled under the Montreal Protocol) decreased substantially during 1990–2004. The emissions, concentrations and radiative forcing of one type of fluorinated gas, the HFCs, grew rapidly during this period as these replaced ODS; in 2004, CFCs were estimated to constitute about 1.1% of the total GHG emissions (100-year GWP) basis. Current annual emissions of all fluorinated gases are estimated at 2.5 GtCO2-eq, with HFCs at 0.4 GtCO2-eq. The stocks of these gases are much larger and currently represent about 21 GtCO2-eq. The largest growth in CO2 emissions has come from the power generation and road transport sectors, with the industry, households and the service sector remaining at approximately the same levels between 1970 and 2004 (Figure 1.2). By 2004, CO2 emissions from power generation represented over 27% of the total anthropogenic CO2 emissions and the power sector was by far its most important source. Following the sectoral breakdown adopted in this report (Chapters 4–10), in 2004 about 26% of GHG emissions were derived from energy supply (electricity and heat generation), about 19% from industry, 14% from agriculture, 17% from land use and land-use change, 13% from transport, 8% from the residential, commercial and service sectors and 3% from waste (see Figure 1.3). These values should be regarded as indicative only as some uncertainty remains, particularly with regards to CH4 and N2O emissions, for which the error margin is estimated to be in the order of 30–50%, and CO2 emissions from agriculture, which have an even larger error margin. Since 1970, GHG emissions from the energy supply sector have grown by over 145%, while those from the transport sector have grown by over 120%; as such, these two sectors show the largest growth in GHG emissions. The industry sector’s emissions have grown by close to 65%, LULUCF (land use, land-use change and forestry) by 40% while the agriculture sector (27%) and residential/commercial sector (26%) have experienced the slowest growth between 1970 and 2004. The land-use change and forestry sector plays a significant role in the overall carbon balance of the atmosphere. However, data in this area are more uncertain than those for other sectors. The Edgar database indicates that, in 2004, the share of CO2 emissions from deforestation and the loss of carbon from soil decay after logging constituted approximately 7–16% of the total GHG emissions (not including ODS) and between 11 and 28% of fossil CO2 emissions. Estimates vary considerably. There are large emissions from deforestation and other land-use change activities in the tropics; these have been estimated in IPCC (2007a) for the 1990s to have been 5.9 GtCO2-eq, with a large uncertainty range of 1.8–9.9 GtCO2-eq (Denman et al., 2007). This is about 25% (range: 8–42%) of all fossil fuel and cement emissions during the 1990s. The underlying factors accounting for the large range in the estimates of tropical deforestation and land-use changes emissions are complex and not fully resolved at this time (Ramankutty et al., 2006). For the Annex I Parties that have reported LULUCF sector data to the UNFCCC (including agricultural soils and forests) since 1990, the aggregate net sink reported for emissions and removals over the period up to 2004 average out to approximately 1.3 GtCO2-eq (range: –1.5 to –0.9 GtCO2-eq). On a geographic basis, there are important differences between regions. North America, Asia and the Middle East have driven the rise in emissions since 1972. The former countries of the Soviet Union have shown significant reductions in CO2 emissions since 1990, reaching a level slightly lower than that in 1972. Developed countries (UNFCCC Annex I countries) hold a 20% share in the world population but account for 46.4% of global GHG emissions. In contrast, the 80% of the world population living in developing countries (non-Annex I countries) account for 53.6% of GHG emissions (see Figure 1.4a). Based on the metric of GHG emission per unit of economic output (GHG/GDPppp), Annex I countries generally display lower GHG intensities per unit of economic production process than non-Annex I countries (see Figure 1.4b). The promotion of energy efficiency improvements and fuel switching are among the most frequently applied policy measures that result in mitigation of GHG emissions. Although they may not necessarily be targeted at GHG emission mitigation, such policy measures do have a strong impact in lowering the emission level from where it would be otherwise. According to an analysis of GHG mitigation activities in selected developing countries by Chandler et al. (2002), the substitution of gasoline-fuelled cars with ethanol-fuelled cars and that of conventional CHP (combined heat and power; also cogeneration) plants with sugar-cane bagasse CHP plants in Brazil resulted in an estimated carbon emission abatement of 23.5 MtCO2 in 2000 (actual emissions in 2000: 334 MtCO2). According to the same study, economic and energy reforms in China curbed the use of low-grade coal, resulting in avoided emissions of some 366 MtCO2 (actual emissions: 3,100 MtCO2). In India, energy policy initiatives including demand-side efficiency improvements are estimated to have reduced emissions by 66 MtCO2 (compared with the actual emission level of 1,060 MtCO2). In Mexico, the switch to natural gas, the promotion of efficiency improvements and lower deforestation are estimated to have resulted in 37 MtCO2 of emission reductions, compared with actual emissions of 685 MtCO2. For the EU-25 countries, the European Environment Agency (EEA, 2006) provides a rough estimate of the avoided CO2 emissions from public electricity and heat generation due to efficiency improvements and fuel switching. If the efficiency and fuel mix had remained at their 1990 values, emissions in 2003 would have been some 34% above actual emissions, however linking these reductions to specific policies was found to be difficult. For the UK and Germany about 60% of the reductions from 1990 to 2000 were found to be due to factors other than the effects of climate-related policies (Eichhammer et al., 2001, 2002). Since 2000, however, many more policies have been put into place, including those falling under the European Climate Change Programme (ECCP), and significant progress has been made, including the establishment of the EU Emissions Trading Scheme (EU ETS) (CEC, 2006). A review of the effectiveness of the first stage of the ECCP reported that about one third of the potential reductions had been fully implemented by mid 2006. Overall EU-25 emissions in 2004 were 0.9% lower than in the base year, and the European Commission (EC) assessed the EC Kyoto target (8% reduction relative to the base year) to be within reach under the conditions that (1) all additional measures currently under discussion are put into force in time, (2) Kyoto mechanisms are used to the full extent planned and (3) removals from Articles 3.3 and 3.4 activities (carbon sinks) contribute to the extent projected (CEC, 2006). Overall this shows that climate policies can be effective, but that they are difficult to fully implement and require continual improvement in order to achieve the desired objectives. |
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