The impact of policy and model uncertainties on emissions projections of the Paris Agreement pledges

The most important contributing factor to the uncertainty in measuring historical emissions, including land-use, is reflected by different datasets. There are two equally important contributing factors globally: socio-economic baseline uncertainty, and uncertainty about the emissions implied by current policies in the case NDCs are less ambitious than the former. 

Overall, the impact of policy uncertainty (i.e. uncertainty resulting from conditionality of or ranges in NDC targets and uncertainty in emissions resulting from current policies) is equally as important as model/technical uncertainty (i.e. uncertainty in historical emissions and socio-economic baseline variations).

This new insight is important for decision-makers and researchers because a larger share of the total uncertainty is now attributable to aspects that can be influenced by policy decisions compared to previous analyses of NDC uncertainty.