Editing IPCC:AR6/WGIII/Chapter-4 (section)

==== 4.2.2.8 Uncertainty in Estimates ====

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There are many factors that influence the global aggregated effects of NDCs. There is limited literature on systematically analysing the impact of uncertainties on the NDC projections with some exception ( [[#Rogelj--2017|Rogelj et al. 2017]] ; Benveniste et al. 2018). The UNEP Gap Report ( [[#UNEP--2017a|UNEP 2017a]] ) discusses uncertainties of NDC estimates in some detail. The main factors include variations in overall socio-economic development; uncertainties in GHG inventories; conditionality; targets with ranges or for single years; accounting of biomass; and different GHG aggregation metrics (e.g., GWP values from different IPCC assessments). In addition, when mitigation effort in NDCs is described as measures that do only indirectly translate into emission reductions, assumptions necessary for the translation come into play ( [[#Doelle--2019|Doelle 2019]] ). For a more elaborate discussion of uncertainties in NDCs ( [[IPCC:Wg3:Chapter:Chapter-14#14.3.2|Section 14.3.2]] ).

Some studies assume successful implementation of all of the NDCs’ proposed measures, sometimes including varying assumptions to account for some of the NDC features which are subject to assumed conditions related to finance and technology transfer. Countries ‘shall pursue domestic mitigation measures’ under Article 4.2 of the Paris Agreement ( [[#UNFCCC--2015a|UNFCCC 2015a]] ), but they are not legally bound to the result of reducing emissions ( [[#Winkler--2017a|Winkler 2017a]] ). Some authors consider this to be a lack of a strong guarantee that mitigation targets in NDCs will be implemented ( [[#Nemet--2017|Nemet et al. 2017]] ). Others point to growing extent of national legislation to provide a legal basis for action ( [[#Iacobuta--2018|Iacobuta et al. 2018]] ) ( [[IPCC:Wg3:Chapter:Chapter-13#13.2|Section 13.2]] ). These factors together with incomplete information in NDCs mean there is uncertainty about the estimates of anticipated 2030 emission levels.

The aggregation of targets results in large uncertainty ( [[#Rogelj--2017|Rogelj et al. 2017]] ; Benveniste et al. 2018). In particular, clarity on the contributions from the land use sector to NDCs is needed ‘to prevent high LULUCF uncertainties from undermining the strength and clarity of mitigation in other sectors’ ( [[#Fyson--2019|Fyson and Jeffery 2019]] ). Methodological differences in the accounting of the LULUCF anthropogenic CO 2 sink between scientific studies and national GHG inventories (as submitted to UNFCCC) further complicate the comparison and aggregation of emissions of NDC implementation ( [[#Grassi--2018|Grassi et al. 2018]] , 2021) ( [[IPCC:Wg3:Chapter:Chapter-7#7.2.3|Section 7.2.3]] and Cross-Chapter Box 6 in Chapter 7). This uncertainty could be reduced with clearer guidelines for compiling future NDCs, in particular when it comes to mitigation efforts not expressed as absolute economy-wide targets ( [[#Doelle--2019|Doelle 2019]] ), and explicit specification of technical details, including energy accounting methods, harmonised emission inventories ( [[#Rogelj--2017|Rogelj et al. 2017]] ) and finally, increased transparency and comparability ( [[#Pauw--2018|Pauw et al. 2018]] ).

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