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

1 Introduction

Structure of the report, the rationale behind it, the role of cross-cutting themes and framing issues

The main aim of this report is to assess options for mitigating climate change. Several aspects link climate change with development issues. This report explores these links in detail, and illustrates where climate change and sustainable development are mutually reinforcing.

Economic development needs, resource endowments and mitigative and adaptive capacities differ across regions. There is no one-size-fits-all approach to the climate change problem, and solutions need to be regionally differentiated to reflect different socio-economic conditions and, to a lesser extent, geographical differences. Although this report has a global focus, an attempt is made to differentiate the assessment of scientific and technical findings for the various regions.

Given that mitigation options vary significantly between economic sectors, it was decided to use the economic sectors to organize the material on short- to medium-term mitigation options. Contrary to what was done in the Third Assessment Report, all relevant aspects of sectoral mitigation options, such as technology, cost, policies etc., are discussed together, to provide the user with a comprehensive discussion of the sectoral mitigation options.

Consequently, the report has four parts. Part A (Chapters 1 and 2) includes the introduction and sets out the frameworks to describe mitigation of climate change in the context of other policies and decision-making. It introduces important concepts (e.g., risk and uncertainty, mitigation and adaptation relationships, distributional and equity aspects and regional integration) and defines important terms used throughout the report. Part B (Chapter 3) assesses long-term stabilization targets, how to get there and what the associated costs are, by examining mitigation scenarios for ranges of stability targets. The relation between adaptation, mitigation and climate change damage avoided is also discussed, in the light of decision-making regarding stabilization (Art. 2 UNFCCC). Part C (Chapters 410) focuses on the detailed description of the various sectors responsible for greenhouse gas (GHG) emissions, the short- to medium-term mitigation options and costs in these sectors, the policies for achieving mitigation, the barriers to getting there and the relationship with adaptation and other policies that affect GHG emissions. Part D (Chapters 1113) assesses cross-sectoral issues, sustainable development and national and international aspects. Chapter 11 covers the aggregated mitigation potential, macro-economic impacts, technology development and transfer, synergies, and trade-offs with other policies and cross-border influences (or spill-over effects). Chapter 12 links climate mitigation with sustainable development. Chapter 13 assesses domestic climate policies and various forms of international cooperation. This Technical Summary has an additional Chapter 14, which deals with gaps in knowledge.

Past, present and future: emission trends

Emissions of the GHGs covered by the Kyoto Protocol increased by about 70% (from 28.7 to. 49.0 GtCO2-eq) from 1970–2004 (by 24% from 1990–2004), with carbon dioxide (CO2) being the largest source, having grown by about 80% (see Figure TS.1). The largest growth in CO2 emissions has come from power generation and road transport. Methane (CH4) emissions rose by about 40% from 1970, with an 85% increase from the combustion and use of fossil fuels. Agriculture, however, is the largest source of CH4 emissions. Nitrous oxide (N2O) emissions grew by about 50%, due mainly to increased use of fertilizer and the growth of agriculture. Industrial emission of N2O fell during this period (high agreement, much evidence) [1.3].

Emissions of ozone-depleting substances (ODS) controlled under the Montreal Protocol (which includes GHGs chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs)), increased from a low level in 1970 to about 7.5 GtCO2-eq in 1990 (about 20% of total GHG emissions, not shown in the Figure TS.1), but then decreased to about 1.5 GtCO2-eq in 2004, and are projected to decrease further due to the phase-out of CFCs in developing countries. Emissions of the fluorinated gases (F-gases) (hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and SF6) controlled under the Kyoto Protocol grew rapidly (primarily HFCs) during the 1990s as they replaced ODS to a substantial extent and were estimated at about 0.5 GtCO2eq in 2004 (about 1.1% of total emissions on a 100-year global warming potential (GWP) basis) (high agreement, much evidence) [1.3].

Figure TS.1

Figure TS.1a: Global anthropogenic greenhouse gas emissions, 1970–2004. One hundred year global warming potentials (GWPs) from IPCC 1996 (SAR) were used to convert emissions to CO2-eq. (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 (in the order of 30-50%) and even larger for CO2 from agriculture and forestry. [Figure 1.1a].


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 bioenergy 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.

Figure TS.1

Figure TS.1b: Global anthropogenic greenhousegas emissions in 2004

[Figure 1.1b].

Atmospheric CO2 concentrations have increased by almost 100 ppm since their pre-industrial level, reaching 379 ppm in 2005, with mean annual growth rates in the 2000-2005 period higher than in the 1990s. The total CO2-equivalent (CO2-eq) concentration of all long-lived GHGs is now about 455 ppm CO2-eq. Incorporating the cooling effect of aerosols, other air pollutants and gases released from land-use change into the equivalent concentration, leads to an effective 311-435 ppm CO2-eq concentration (high agreement, much evidence).

Considerable uncertainties still surround the estimates of anthropogenic aerosol emissions. As regards global sulphur emissions, these appear to have declined from 75 ± 10 MtS in 1990 to 55-62 MtS in 2000. Data on non-sulphur aerosols are sparse and highly speculative. (medium agreement, medium evidence).

In 2004, energy supply accounted for about 26% of GHG emissions, industry 19%, gases released from land-use change and forestry 17%, agriculture 14%, transport 13%, residential, commercial and service sectors 8% and waste 3% (see Figure TS.2). These figures should be seen as indicative, as some uncertainty remains, particularly with regards to CH4 and N2O emissions (error margin estimated to be in the order of 30-50%) and CO2 emissions from agriculture and forestry with an even higher error margin (high agreement, medium evidence) [1.3].

Figure TS.2

Figure TS.2a: GHG emissions by sector in 1990 and 2004 100-year GWPs from IPCC 1996 (Second Assessment Report (SAR)) were used to convert emissions to CO2-eq. The uncertainty in the graph is quite large for CH4 and N2O (in the order of 30–50%) and even larger for CO2 from agriculture and forestry. For large-scale biomass burning, averaged activity data for 1997–2002 were used from Global Fire Emissions Database based on satellite data. Peat (fire and decay) emissions are based on recent data from WL/Delft Hydraulics. [Figure 1.3a]

Figure TS.2

Figure TS.2b: GHG emissions by sector in 2004 [Figure 1.3b].

Notes to Figure TS.2a and 2b:

1) Excluding refineries, coke ovens etc., which are included in industry.

2) Including international transport (bunkers), excluding fisheries. Excluding off-road agricultural and forestry vehicles and machinery.

3) Including traditional biomass use. Emissions in Chapter 6 are also reported on the basis of end-use allocation (including the sector’s share in emissions caused by centralized electricity generation) so that any mitigation achievements in the sector resulting from lower electricity use are credited to the sector.

4) Including refineries, coke ovens etc. Emissions reported in Chapter 7 are also reported on the basis of end-use allocation (including the sector’s share in emissions caused by centralized electricity generation) so that any mitigation achievements in the sector resulting from lower electricity use are credited to the sector.

5) Including agricultural waste burning and savannah burning (non-CO2). CO2 emissions and/or removals from agricultural soils are not estimated in this database.

6) Data include CO2 emissions from deforestation, 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. Chapter 9 reports emissions from deforestation only.

7) Includes landfill CH4, wastewater CH4 and N2O, and CO2 from waste incineration (fossil carbon only).

Figure TS.3 identifies the individual contributions to energy-related CO2 emissions from changes in population, income per capita (gross domestic product (GDP) expressed in terms of purchasing-power parity per person - GDPppp/cap[1]), energy intensity (Total Primary Energy Supply (TPES)/GDPppp), and carbon intensity (CO2/TPES). Some of these factors boost CO2 emissions (bars above the zero line), while others lower them (bar below the zero line). The actual change in emissions per decade is shown by the dashed black lines. According to Figure TS.3, the increase in population and GDP-ppp/cap (and therefore energy use per capita) have outweighed and are projected to continue to outweigh the decrease in energy intensities (TPES/GDPppp) and conceal the fact that CO2 emissions per unit of GDPppp are 40% lower today than during the early 1970s and have declined faster than primary energy per unit of GDPppp or CO2 per unit of primary energy. The carbon intensity of energy supply (CO2/TPES) had an offsetting effect on CO2 emissions between the mid 1980s and 2000, but has since been increasing and is projected to have no such effect after 2010 (high agreement, much evidence) [1.3].

Figure TS.3

Figure TS.3: Decomposition of global energy-related CO2 emission changes at the global scale for three past and three future decades [Figure 1.6].

In 2004, Annex I countries had 20% of the world’s population, but accounted for 46% of global GHG emissions, and the 80% in Non-Annex I countries for only 54%. The contrast between the region with the highest per capita GHG emissions (North America) and the lowest (Non-Annex I South Asia) is even more pronounced (see Figure TS.4a): 5% of the world’s population (North America) emits 19.4%, while 30.3% (Non-Annex I South Asia) emits 13.1%. A different picture emerges if the metric GHG emissions per unit of GDPppp is used (see Figure TS.4b). In these terms, Annex I countries generated 57% of gross world product with a GHG intensity of production of 0.68 kg CO2-eq/US$ GDPppp (non-Annex I countries 1.06 kg CO2-eq/US$ GDPppp) (high agreement, much evidence) [1.3].

Figure TS.4

Figure TS.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 [Figure 1.4a].

Figure TS.4

Figure TS.4b: Distribution of regional GHG emissions (all Kyoto gases including those from land-use) per US$ 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 [Figure 1.4b].

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.

Global energy use and supply – the main drivers of GHG emissions – is projected to continue to grow, especially as developing countries pursue industrialization. Should there be no change in energy policies, the energy mix supplied to run the global economy in the 2025–30 timeframe will essentially remain unchanged, with more than 80% of energy supply based on fossil fuels with consequent implications for GHG emissions. On this basis, the projected emissions of energy-related CO2 in 2030 are 40–110% higher than in 2000, with two thirds to three quarters of this increase originating in non-Annex I countries, though per capita emissions in developed countries will remain substantially higher, that is 9.6 tCO2/cap to 15.1 tCO2/cap in Annex I regions versus 2.8 tCO2/cap to 5.1 tCO2/cap in non-Annex I regions (high agreement, much evidence) [1.3].

For 2030, projections of total GHG emissions (Kyoto gases) consistently show an increase of 25–90% compared with 2000, with more recent projections higher than earlier ones (high agreement, much evidence).

For 2100, the SRES[2] range (a 40% decline to 250% increase compared with 2000) is still valid. More recent projections tend to be higher: increase of 90% to 250% compared with 2000 (see Figure TS.5). Scenarios that account for climate policies, whose implementation is currently under discussion, also show global emissions rising for many decades.

Figure TS.5

Figure TS.5: Global GHG emissions for 2000 and projected baseline emissions for 2030 and 2100 from IPCC SRES and the post-SRES literature. The figure provides the emissions from the six illustrative SRES scenarios. It also provides the frequency distribution of the emissions in the post-SRES scenarios (5th, 25th, median, 75th, 95th percentile), as covered in Chapter 3. F-gases cover HFCs, PFCs and SF6 [Figure 1.7].

Developing countries (e.g., Brazil, China, India and Mexico) that have undertaken efforts for reasons other than climate change have reduced their emissions growth over the past three decades by approximately 500 million tonnes CO2 per year; that is, more than the reductions required from Annex I countries by the Kyoto Protocol. Many of these efforts are motivated by economic development and poverty alleviation, energy security and local environmental protection. The most promising policy approaches, therefore, seem to be those that capitalize on natural synergies between climate protection and development priorities to advance both simultaneously (high agreement, medium evidence) [1.3].

  1. ^  The GDPppp metric is used for illustrative purposes only for this report.
  2. ^  SRES refers to scenarios described in the IPCC Special Report on Emission Scenarios (IPCC, 2000b). The A1 family of scenarios describes a future with very rapid economic growth, low population growth and rapid introduction of new and more efficient technologies. B1 describes a convergent world, with the same global population that peaks in mid century and declines thereafter, with rapid changes in economic structures. B2 describes a world ‘in which emphasis is on local solutions to economic, social, and environmental sustainability’. It features moderate population growth, intermediate levels of economic development, and less rapid and more diverse technological change than the A1B scenario.