Footnotes for Summary for Policymakers

1. The open process defined in the Special Report on Emissions Scenarios (SRES) Terms of Reference calls for the use of multiple models, seeking inputs from a wide community as well as making scenario results widely available for comments and review. These objectives were fulfilled by the SRES multi-model approach and the open SRES website.

2. Included are anthropogenic emissions of carbon dioxide (CO₂ ), methane (CH₄), nitrous oxide (N₂O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF₆ ), hydrochloro-fluorocarbons (HCFCs), chlorofluorocarbons (CFCs), the aerosol precursor and the chemically active gases sulfur dioxide (SO₂), carbon monoxide (CO), nitrogen oxides (NO_x), and non-methane volatile organic compounds (NMVOCs). Emissions are provided aggregated into four world regions and global totals. In the new scenarios no feedback effect of future climate change on emissions from biosphere and energy has been assumed.

3. Balanced is defined as not relying too heavily on one particular energy source, on the assumption that similar improvement rates apply to all energy supply and end use technologies.

4. Technological change is not quantified in table SPM-1.

5. Because of the impossibility of including the complex way land use is changing between the various land use types, this information is not in the table.

6. Therefore, the ranges of non-CO₂ GHG emissions provided in the Report may not fully reflect the level of uncertainty compared
to CO₂ , for example only a single model provided the sole value for halocarbon emissions.

7. In the new scenarios no feedback effect of future climate change on emissions from the biosphere has been assumed.

8. In this Report, cumulative emissions are calculated by adding annual net anthropogenic emissions in the scenarios over their time horizon. When relating these cumulative emissions to atmospheric concentrations, all natural processes that affect carbon concentrations in the atmosphere have to be taken into account.

9. Although global emissions of SO for the SRES scenarios are lower than the IS92 scenarios, uncertainty about SO emissions and their effect on sulfate aerosols has increased compared to the IS92 scenarios because of very diverse regional patterns of SO₂ emissions in the scenarios.

10. Confidence in the quantification of any scenario decreases substantially as the time horizon increases because the basis for the assumptions becomes increasingly speculative. This is why a set of scenarios was developed.