Regardless of differences in emission volume (i.e., sector coverage), studies may have different values for historical emissions, i.e. before the start of a study (the year in which the study calculations begin). This is because the underlying models often use different data sources for historical emissions. The differences can be considerable, especially in countries where the share of CO2 emissions is high. (a) regional contributions to global emissions and uncertainties related to the full implementation of current NPOs. The nuances indicate the minimum to the maximum value of emissions estimates by region; (b) estimate of the magnitude of source-by-source uncertainty in 2030 relative to the median estimate; (c) the average contribution to the total uncertainty margin in 2030, by source of uncertainty, with the 10 largest contributions identified by region; (d) as b, but by geographic region. AFR, sub-Saharan Africa; The CPA, Asia and China, in central project; EEU, Central and Eastern Europe; FSU, former Soviet Union; LAM, Latin America and the Caribbean; MEA, Middle East and North Africa; NAM, North America; NOT, OECD Pacific; SAS, South Asia; NOT, Other Asia Pacific; WEU, Western Europe. National borders use the simplified TM World borders provided by Bjorn Sandvik (thematicmapping.org). Similarly, the vagueness of historical emissions inventories creates uncertainty in NPN estimates, up to 10% in developing countries (LAM and AFR), which have had to end less often in the past, and in processing economies (SAFs). Changes in historical emissions inventories change the starting points of the baselines relative to the reductions. For FSU, one of the three historical sets of emissions data we use in this analysis, reported 14-16% less emissions in 1990 compared to the other two data sets.
Fluctuations in historical emissions inventories also affect other regions where many countries report that their NPCs are reductions from a fixed historical base year (such as NAM, WEU, EEU and PAO). However, the relative variation in this contribution is small and never exceeds 4%.