NDC and Greenhouse Gas Emission Pathways

The COP 21 in Paris decided to start a ratchet up mechanism in 2018 that leads to progressive nationally determined contributions (NDC). If the connection between the cumulative CO2 emissions and global warming, as described in the IPCC Fifth Assessment Report, is taken seriously, the question arises whether the progressive NDCs submitted by the countries allocate this remaining CO2 budget in a fair and reasonable manner. Resource sharing models directly address the allocation of such a remaining global budget. In existing models parameters are not clearly described. It seems that some researchers in that field are more interested in the results - who will receive how much of the remaining budget? - than in a coherent model.

This project is aimed to develop such a coherent model and compare it to resource sharing models like convergence models or the smooth pathway models.

Under certain conditions convergence models have an implicit weighting of the population depending on the chosen global path. This implicit weighting arises when a globally remaining budget is split directly into countries with a weighted key consisting of "current emissions" and "current population" in the same national budgets as in the respective convergence model.


Comparison of resource sharing models regarding pathways of t per capita emissions

The comparison of resource sharing models using three pure type countries has revealed significant differences. This differences are relevant when discussing reference values for the NDCs in the ratchet up mechanism of Paris.


In our model (Sargl , et al. 2017) the emissions of country i in the year t  are derived from




Smooth pathway models (SPM) have the advantage that climate justice is addressed explicitly and does not depend on a global pathway. Furthermore, SPM lead to smooth pathways until infinity. Other models might give hints of the range of the weighting of population when it comes to determining remaining national budgets as an input value in SPM. If any other model is used to justify or to assess NDCs, the underlying global pathway must be disclosed, because its results depend on the selected global pathway.

Comparison of SPM (weighting of population = 16%) and our model (RM)


Our model is, beside smooth pathways models, the most favourable resource sharing model for industrial countries. Therefore, national emission pathways calculated with our model describe a floor of ambition for industrial countries if they accept to take into account equal per capita rights. Otherwise they will have difficulty explaining their NDCs if they fall below this floor. As an example our model means for the EU that it has to reduce emissions in comparison to 1990 rather in a scale of 50% than only 40% proposed so far. (cf. Sargl, et al., 2017, p. 672)


The question of the convergence of the per capita emissions as a property of a model becomes less important the sooner global emissions must be zero or even negative. The later global emissions begin to decline, the sooner emission neutrality has to be reached, due to the budget property of CO2.

In SPM it is not necessary to determine a global pathway when allocating the global remaining budget to countries, but it would be useful to agree on a suitable global pathway, after having agreed on a remaining global CO2 budget compatible with the 2 C  limit. This would enable an effective control of deviations. A global pathway would not be carved in stone, but could be constantly adapted to the latest developments and scientific status.

Considering the ratchet up mechanism of Paris the focus should be on the remaining national budgets seen as a fair and reasonable share of the remaining global budget. Resource sharing models give useful help when it comes to determining these budgets. It would make sense to calculate the weighting of the allocation keys “current population” and “current emissions” leading to the same remaining national budgets, resulting from NDCs. This makes clear, which weighting of “current population” is considered as legitimate. Thus, the weighting of population could contribute to a more rational discourse of the core question: Who will get how much of the remaining global budget.



Sargl, M., Wolfsteiner, A. & Wittmann, G. (2017): The Regensburg Model: reference values for the (I)NDCs based on converging per capita emissions. Climate Policy, 17(5), p. 664 – 677.

Sargl M./ Wittmann G./ Wolfsteiner A. (2015): The Regensburg Model: Emission Trading between Countries Based on Global CO2 Budgets In: Critical Issues in Environmental Taxation Volume XV Ed: Larry Kreiser u.a. Edward Elgar Publishing 2015 P.76-92.

Sargl M./ Wittmann G./ Wolfsteiner A. (2015): Mindestreferenzwerte für CO2-Emissionen. In Wirtschaftsdienst Heft 7 2015, S.494-498