IPCC Fourth Assessment Report: Climate Change 2007
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[5] (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.

Figure 1.1

Figure 1.1a Global anthropogenic greenhouse gas trends, 1970–2004.

One-hundred year global warming potentials (GWPs) from the Intergovernmental Panel on Climate Change (IPCC) 1996 (SAR) were used to convert emissions to CO2 equivalents (see the UNFCCC reporting guidelines). Gases are those reported under UNFCCC reporting guidelines. The uncertainty in the graph is quite large for CH4 and N2O (of the order of 30–50%) and even larger for CO2 from agriculture and forestry.


1. Other N2O includes industrial processes, deforestation/savannah burning, waste water and waste incineration.

2. Other is CH4 from industrial processes and savannah burning.

3. Including emissions from bio energy production and use.

4. CO2 emissions from decay (decomposition) of above ground biomass that remains after logging and deforestation and CO2 from peat fires and decay of drained peat soils.

5. As well as traditional biomass use at 10% of total, assuming 90% is from sustainable biomass production. Corrected for the 10% of carbon in biomass that is assumed to remain as charcoal after combustion.

6. For large-scale forest and scrubland biomass burning averaged data for 1997-2002 based on Global Fire Emissions Data base satellite data.

7. Cement production and natural gas flaring.

8. Fossil fuel use includes emissions from feedstocks.

Source: Adapted from Olivier et al., 2005; 2006; Hooijer et al., 2006

Figure 1.1

Figure 1.1b Global anthropogenic greenhouse gas emissions in 2004.

Source: Adapted from Olivier et al., 2005, 2006

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[6] 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 410), in 2004 about 26% of GHG emissions were derived from energy supply (electricity and heat generation), about 19% from industry, 14% from agriculture[7], 17% from land use and land-use change[8], 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.

Figure 1.2

Figure 1.2: Sources of global CO2 emissions, 1970–2004 (only direct emissions by sector).

1) Including fuelwood at 10% net contribution. For large-scale biomass burning, averaged data for 1997–2002 are based on the Global Fire Emissions Database satellite data (van der Werf et al., 2003). Including decomposition and peat fires (Hooijer et al., 2006). Excluding fossil fuel fires.

2) Other domestic surface transport, non-energetic use of fuels, cement production and venting/flaring of gas from oil production.

3) Including aviation and marine transport.

Source: Adapted from Olivier et al., 2005; 2006).

Figure 1.3

Figure 1.3a: GHG emissions by sector in 1990 and 2004.

Source: Adapted from Olivier et al., 2005, 2006.

Figure 1.3

Figure 1.3b: GHG emissions by sector in 2004.

Source: Adapted from Olivier et al., 2005; 2006.

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)[9].

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)[10], Annex I countries generally display lower GHG intensities per unit of economic production process than non-Annex I countries (see Figure 1.4b).

Figure 1.4

Figure 1.4a: Distribution of regional per capita GHG emissions (all Kyoto gases including those from land-use) over the population of different country groupings in 2004. The percentages in the bars indicate a region’s share in global GHG emissions.

Source: Adapted from Bolin and Khesgi, 2001) using IEA and EDGAR 3.2 database information (Olivier et al., 2005, 2006).

Figure 1.4

Figure 1.4b: Distribution of regional GHG emissions (all Kyoto gases including those from land-use) per USD of GDPppp over the GDP of different country groupings in 2004. The percentages in the bars indicate a region’s share in global GHG emissions.

Source: IEA and EDGAR 3.2 database information (Olivier et al., 2005, 2006).

Note: Countries are grouped according to the classification of the UNFCCC and its Kyoto Protocol; this means that countries that have joined the European Union since then are still listed under EIT Annex I. A full set of data for all countries for 2004 was not available. The countries in each of the regional groupings include:

  • EIT Annex I: Belarus, Bulgaria, Croatia, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania, Russian Federation, Slovakia, Slovenia, Ukraine
  • Europe Annex II & M&T: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Liechtenstein, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, United Kingdom; Monaco and Turkey
  • JANZ: Japan, Australia, New Zealand.
  • Middle East: Bahrain, Islamic Republic of Iran, Israel, Jordan, Kuwait, Lebanon, Oman, Qatar, Saudi Arabia, Syria, United Arab Emirates, Yemen
  • Latin America & the Caribbean: Antigua & Barbuda, Argentina, Bahamas, Barbados, Belize, Bolivia, Brazil, Chile, Colombia, Costa Rica, Cuba, Dominica, Dominican Republic, Ecuador, El Salvador, Grenada, Guatemala, Guyana, Haiti, Honduras, Jamaica, Mexico, Nicaragua, Panama, Paraguay, Peru, Saint Lucia, St. Kitts-Nevis-Anguilla, St. Vincent-Grenadines, Suriname, Trinidad and Tobago, Uruguay, Venezuela
  • Non-Annex I East Asia: Cambodia, China, Korea (DPR), Laos (PDR), Mongolia, Republic of Korea, Viet Nam.
  • South Asia: Afghanistan, Bangladesh, Bhutan, Comoros, Cook Islands, Fiji, India, Indonesia, Kiribati, Malaysia, Maldives, Marshall Islands, Micronesia, (Federated States of), Myanmar, Nauru, Niue, Nepal, Pakistan, Palau, Papua New Guinea, Philippine, Samoa, Singapore, Solomon Islands, Sri Lanka, Thailand, Timor-Leste, Tonga, Tuvalu, Vanuatu
  • North America: Canada, United States of America.
  • Other non-Annex I: Albania, Armenia, Azerbaijan, Bosnia Herzegovina, Cyprus, Georgia, Kazakhstan, Kyrgyzstan, Malta, Moldova, San Marino, Serbia, Tajikistan, Turkmenistan, Uzbekistan, Republic of Macedonia
  • Africa: Algeria, Angola, Benin, Botswana, Burkina Faso, Burundi, Cameroon, Cape Verde, Central African Republic, Chad, Congo, Democratic Republic of Congo, Côte d’Ivoire, Djibouti, Egypt, Equatorial Guinea, Eritrea, Ethiopia, Gabon, Gambia, Ghana, Guinea, Guinea-Bissau, Kenya, Lesotho, Liberia, Libya, Madagascar, Malawi, Mali, Mauritania, Mauritius, Morocco, Mozambique, Namibia, Niger, Nigeria, Rwanda, Sao Tome and Principe, Senegal, Seychelles, Sierra Leone, South Africa, Sudan, Swaziland, Togo, Tunisia, Uganda, United Republic of Tanzania, Zambia, Zimbabwe

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[11]. 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.

  1. ^  Radiative forcing (Forster et al., 2007) is converted to CO2 equivalents using the inversion of the expression Q (W/m2) = 5.35 × ln (CO2/278) (see Solomon et al., 2007,
  2. ^  Direct emissions by sector; i.e., data do not include indirect emissions.
  3. ^  N2O and CH4 emissions (CO2 emissions are small; compare with Chapter 8) and not counting land clearance. The proportion of emissions of N2O and CH4 are higher – around 85 and 45% (±5%), respectively. Emissions from agricultural soils not related to land clearance are quite small – of an order of 40 MtCO2 per year in 2005 (Chapter 8).
  4. ^  Deforestation, including biofuel combustion, assuming 90% sustainable production, biomass burning, CO2 emissions from the decay of aboveground biomass after logging and deforestation and from peat fires and decay of peat soils.
  5. ^  Data for the Russian Federation is not included in the UNFCCC data set. Chapter 7 estimates the Russian sink for 1990–2000 to be 370–740 MtCO2/year, which would add up to approximately 28–57% of the average sink reported here.
  6. ^  The GDPppp metric is used for illustrative purposes only for this report.
  7. ^  See Table 1 of CEC (2006). Second stage ECCP (ECCP2) policies are being finalized.