The following conventions and caveats apply to the data and analysis presented in this report:

• Data Sources. Most information presented in this report is drawn from CAIT version 3.0 (see Appendix 1 Climate Analysis Indicator Tool). Where no data source is provided, it can be presumed that CAIT is the source. This report—and CAIT—use data from a wide variety of sources, including the Carbon Dioxide Information Analysis Center (Marland et al., 2005); Houghton (2003a); the Intergovernmental Panel on Climate Change (IPCC, 2000a); International Energy Agency (IEA, 2004a); U.S. Environmental Protection Agency (EPA, 2004); U.S. Energy Information Administration (EIA, 2003, 2004); RIVM/TNO (2003); and the UN Framework Convention on Climate Change (UNFCCC, 2005). 9 For more information, see Appendices 1 and 2 and the CAIT website (http://cait.wri.org).
• Definition of Sectors. When examining GHG emissions, this report follows the sector and subsector definitions adopted by the IPCC (1997). However, there are many exceptions that are explained in Appendix 2, endnotes, and supporting documentation to CAIT (WRI, 2005a; WRI, 2005b). In some cases, the report deviates from IPCC guidelines because the underlying GHG data sources do not match IPCC definitions. In other cases, definitions are refined to enable a more comprehensive accounting of a particular end-use activity (for example, combining energyrelated emissions with industrial process-related emissions for cement).
• Treatment of Different Gases and Sources. When examining GHG emissions, this report's default approach is to include six greenhouse gases: CO2, CH4, N2O, sulfur hexafluoride (SF6), per-fluorocarbons (PFCs), and hydrofluorocarbons (HFCs). Unless noted otherwise, CO2 emissions from land-use change and forestry are generally not included in national totals due to large data uncertainties. In addition, data on emissions of non-CO2 gases is generally unavailable after 2000. All emissions figures in this report are expressed in CO2 equivalents, using 100-year global warming potentials from the IPCC (1996).
• Data Uncertainties. In many cases, there is significant uncertainty with respect to emission estimates. This is true even for CO2 from fossil fuels, although uncertainties tend to be smaller in OECD countries (Andres et al., 2000). The largest uncertainties are for CO2 from landuse change and forestry (LUCF). Chapter 17 discusses global and national-level uncertainties for this sector, and caution is urged when analyzing LUCF data. For non-CO2 data, the largest uncertainties tend to be for N2O, followed by CH4 (WRI, 2005a). For more detailed information about uncertainty, readers should also refer to documentation from individual data sources.
• The European Union. The European Union (EU) is in most cases treated as a separate entity. This is because the European Community has acceded to the UNFCCC as a regional economic integration organization, with “Party” status. The EU is typically considered here as a 25-member state body (“EU-25”), rather than the 15-member state body that existed when the EU ratified the Kyoto Protocol. Member states of the EU are also listed in many tables and figures. Where data are summed—for example, emissions of the “top 25 countries”—the EU figure is included in this total, but individual member states are not (to avoid double counting).
• “Developed” and “Developing” Countries. References to “developed” and “developing” countries correspond to the distinction under the UNFCCC between “Annex I” and “non-Annex I” countries (with non-Parties placed accordingly). Annex I includes several economies in transition. See Glossary and Abbreviations.
• Top 25 GHG Emitting Countries. This report frequently selects for analysis the 25 countries with the largest absolute emissions of GHGs. This is done even for most of the indicators analyzed in this report, including gross domestic product, income, population, and others. The report focuses on these countries more than others for reasons of environmental importance and convenience. The intent is not to suggest that these are the only countries of importance for greenhouse gas mitigation; only that they are the most important.
• GDP. In this report, except where noted, gross domestic product (GDP) is measured in units of purchasing power parity. These units, while the subject of some controversy, are believed to be more appropriate than market exchange rates for making international comparisons, especially between developed and developing countries.
• Figures and Tables. Charts, graphs, and tables that appear within the body of this report are referred to as “figures.” Because this report contains a great deal of data, however, supplementary Data Tables are included at the end of the report. Where the text refers to “tables,” readers are directed to those tables. Tables typically provide more quantitative detail than the figures in the body of the report.

(1) This section draws largely on IPCC, 2000a; IPCC, 2001a,b; den Elzen and Meinshausen, 2005.

(2) Such an emissions reduction would achieve a 2 degree C target with a probability exceeding 85 percent. The reduction figure excludes emissions from land-use change and forestry. Significant climate damages may still be associated with a 2 degree C increase in global temperatures. See den Elzen and Meinshausen, 2005.

(3) Author calculations, based on Marland et al., 2005 and Houghton, 2003a.

(4) Author calculations, based on Marland et al., 2005 and Houghton, 2003a.

(5) Author calculations, based on BP, 2005.

(6) Author calculations, based on BP, 2005.

(7) Activities related to land-use change and forestry could also be included here (for example., land clearing). However, the data in this sector does not permit a more detailed analysis.

(8) Measured in carbon dioxide equivalent units, using 100-year global warming potentials from IPCC (1996).

(9) Official GHG inventories submitted by Parties to the UNFCCC are used only sparingly. The primary reason is that UNFCCC data has very limited geographic and temporal coverage.