Also in this chapter:

3.3 Analysis Of Differences Between The Estimates

The range between modeling groups’ estimates can be split into three categories:

  1. Differences between the four pledge cases,
  2. Differences between estimates for the same pledge case, and
  3. Other factors that could affect emissions

More detail on each of these issues and, where appropriate, the sources of estimates can be found online in Appendix 1. Figure 3 summarises the impact of these differences on the emissions of the four pledge cases, together with the further uncertainties described in the next section.

1) Differences between the four pledge cases

The four cases presented in Figure 2 are characterised by different assumptions on the conditionality of both Annex I and non-Annex I countries’ pledges, LULUCF accounting rules and on the use of surplus units from the first commitment period and the possible creation of new surplus in the future. An overview of the impact of these assumptions is provided below
– Appendix 1 has more details:

Unconditional versus conditional pledges
  • Conditionality of Annex I (industrialized) countries (0 to -2.7 GtCO2e)46: A significant number of Annex I countries have made pledges that are conditional on the actions of others or on the passing of domestic legislation. In some instances, countries also have unconditional pledges that will be implemented even if those conditions are not met.
  • Conditionality of non-Annex I (developing) countries (0 to -0.7 GtCO2e)47: As was the case for the Annex I countries, some non-Annex I countries have included a range in their submissions, with the upper end of the range often being conditional on climate finance.
“Lenient” versus “strict” rules

If the rules in the negotiations regarding the use of LULUCF credits and surplus emission units were to be set in a “strict” rather than “lenient” manner, emissions could be around 1-2 GtCO2e lower. This breaks down as follows (numbers in parentheses show the maximum possible increase in annual 2020 emissions reflected in the “lenient” cases)

  • LULUCF accounting rules (0 to +0.8 GtCO2e): The accounting rules that determine the extent to which LULUCF activities in Annex I countries could be used to meet their respective targets for the period after 2012 are still being negotiated. Most proposals in the negotiations would limit the number of “lenient LULUCF credits” by using historical or reference level baselines (see Box 3b).
  • Surplus emission units
    • Carry-over of surplus units from the first commitment period (0 to +1.3 GtCO2e): Surplus emission units can arise due to some countries exceeding their targets in the first commitment period. Countries with surplus units can also “bank” them and use them for meeting their target in a following commitment period post-2012, or sell them to other countries for their compliance.
    • Creation of new surplus units in a possible second commitment period: (0 to +1.0 GtCO2e)48: Further surplus emission units can occur through some countries being allocated emission units significantly above the estimated business-as-usual level in a possible second commitment period. These units can be used by countries to meet their targets, or sell to other countries for their compliance.

It should be noted that the above issues are interdependent and will result in different emission reductions depending on the order in which they are implemented. Hence the numbers presented above cannot simply be added together and are, therefore, not easily traceable to the median results reflected in Figure 2 above49. In the reviewed studies, the total impact from these options (if taken together) would be a reduction in global emissions of 4 GtCO2e (reflected in the move from Case 1 to 4 in the table), with a full range across studies of 3-8 GtCO2e.

Box 3b: For Details on 'Further explanation of LULUCF accounting in “lenient” and “strict” rules', Click Here

2) Differences between estimates for the same pledge case

Figure 2 shows that there is sometimes a large difference between modelling groups’ estimates of the same cases. The main reasons for these differences are described below and, where possible, the uncertainty that each implies for 2020 global emissions. Numbers in parentheses give the range of 2020 emission estimates in Figure 2 that could be attributed to each of these reasons.

  • LULUCF emissions (±4 GtCO2e): Global emissions from LULUCF are subject to a high level of uncertainty, which the IPCC estimates to be ±4 GtCO2e . There is particular uncertainty around anthropogenic emissions from peat lands. Lastly there is an uncertainty around how modelling groups treat the LULUCF emissions from Annex I countries, in particular. LULUCF emission uncertainty may be partially reflected in the range of estimates from different modelling groups.
  • Baseline emissions (-3.4 to +2.4 GtCO2e): Modelling groups have used different assumptions regarding non-Annex I countries’ business-as-usual emission projections and Annex I countries’ base year emissions (e.g. whether LULUCF CO2 is included or not). Moreover, the quantification of emission reductions due to carbon intensity targets (measured as improvement in emissions per unit of GDP) poses additional uncertainties.
  • Non-covered sectors and countries (-1.1 to +2.7 GtCO2e): There is often a significant range in the emissions estimates for sectors not included under national pledges, such as emissions from international aviation and maritime transport (bunkers) and for countries without pledges. The results from different studies will vary, since some have explored the impact of mitigation policies of only a subset of countries.

3) Other factors that could affect emissions

There are a number of other factors not reflected in the range of estimates under each of these cases, but which could have a large impact on 2020 emissions. Modelling groups have generally not factored these issues into their central estimates for emissions resulting from the pledges—although many of the groups have estimated the impact of these issues separately. These factors include the following. Numbers in parentheses give the maximum annual 2020 emissions impact on the four cases:

  • Double counting of offsets (0 to +1.3 GtCO2e): The potential for double counting of offsets towards both industrialized and developing country pledges, is a major source of uncertainty not reflected in Figure 2. This could occur if industrialized countries use offsets to meet their targets and that these same offsets also counted towards developing country pledges. A simple estimate of the risk of double counting can be made by assuming that 33 per cent of the deviation of Annex I emissions from business-as-usual is covered by offsets and that all of those are also counted towards non-Annex I goals. This would lead to emissions being around 1.3 GtCO2e higher (as compared to the “conditional pledge, strict rules” case)52
  • Partial or ineffective delivery (0 to +2.0 GtCO2e): Any failure to carry out policies would undermine national efforts and lead to higher 2020 emissions; this would push countries’ emissions back towards business-as-usual. Conversely, well-designed policies that spur innovation and investment could mean that goals are exceeded. All analyses covered in Figure 2 assume that countries will meet their targets. A crude assessment of the risk of partial implementation can be made by assuming that a certain proportion of the deviation from global business-as-usual is not delivered. Using 25 per cent would lead to estimates of 2020 emissions around 2.0 GtCO2e higher than in Figure 2 (as compared to the ”conditional pledge, strict rules” case)
  • International climate finance (0 to -2.5 GtCO2e): International climate finance could leverage further emission reductions beyond the conditional pledges of countries or in countries that have not yet specified mitigation actions. The upper bound of -2.5 GtCO2e is found by a study that assumes that 25 per cent of Copenhagen Accord financing in 2020 will be used for additional mitigation actions (Carraro and Massetti, 2010).
  • Ambitious domestic policy (0 to -1.5 GtCO2e): Certain countries have domestic plans that include mitigation actions that some analysts estimate to be more ambitious than the Copenhagen Accord pledges. The three modelling groups that have analysed this issue estimate that this could lead to emissions being up to 1.5 GtCO2e lower than the Copenhagen Accord pledges would suggest.
Figure 3: Summary of the maximum impact of differences and uncertainties on global 2020 emissions. There
is a strong interaction between these factors and the effects are therefore not additive. Hence, no estimate of their
total impact is given.



Box 3c: For Details on 'Under what circumstances would the Copenhagen Accord pledges lead to a peak in global emissions before 2020?', Click Here