Modelling of the GDR`s approach is based on status quo (BaU) emissions, which countries do not mutually recognise. The BaU emissions used here are downgraded from RCP8.5, resulting in significantly higher allocations than other allocations for Eastern European countries and Australia. Compared to the CBDR-RC hybrid configuration shown in Fig. 4, the inclusion of the GDR approach in the hybrid configuration leads to a lower rated temperature in favor of the CDNs of Eastern European countries, Australia and South Africa and to a higher rated temperature, which disadvantages India, Brazil, Mexico and Indonesia (Fig. additional 6). The GDR`s approach was developed to assign mitigation measures to people whose income exceeds a certain threshold. The proportion of a country`s population above the income threshold is derived from the Gini Inequality Index16. Although DDR is a complex method that takes into account more indicators than most other approaches in the literature, its use of hypothetical BaU emissions and Gini projections, which are not generally accepted indicators, leads to a significant sensitivity that cannot be easily resolved. The ideas of responsibility and capacity on which the GDR is based are conveyed by the same cumulative approaches per capita (CPC) and per competence (CAP).
An international agreement, as Daniel Bodansky explains, is “not only.. the rigor of its obligations, but also the degree of participation and respect. (Bodansky 2). The problem with a top-down approach is that it is difficult to maintain the participation of a large number of countries because each country has different economic capacities, poverty levels and economic diversity. Make it too strict, and more countries will reject it. The only way to get a significant number of countries to accept an international agreement is to make it less stringent, which will not have enough impact on global emissions to significantly mitigate global warming (Bodansky 2). A bottom-up approach is much better for reducing global emissions, as greater involvement of countries is inevitable as they will have the freedom to implement measures based on their economic capacity, growth rates and the amount of life-saving emissions. However, this bottom-up approach raises a glaring concern that it could lead to a lack of ambition if the individual parties were to decide what action to take.
Countries may care more about their economies in the short term than about mitigating climate change and will take less stringent measures than with a top-down approach.  Synthesis Report on the Aggregate Impact of Intended Nationally Determined Contributions (INDCs) (available at: unfccc.int/files/focus/indc_portal/application/pdf/synthesis_report_-_overview.pdf) [hereinafter referred to as “INDC Synthesis Report”]. For more information on INDCs and their importance for future climate agreements, see World Resources Institute, “What is a INDC?” (available at www.wri.org/indc-definition). Schiermeier, Q. Landmark court ruling calls on the Dutch government to do more to tackle climate change. Nature News, doi.org/10.1038/nature.2015.17841 (2015). We used and extended the Potsdam integrated real-time model for the probabilistic assessment of emission trajectories19.57 (PRIMAP) to model allocation approaches. The database contains historical and projected data on population, GDP and GHG emissions from composite sources, as described in reference 27. Peters, G. P., Andrew, R.M., Solomon, S. & Friedlingstein, P.
Measuring a fair and ambitious climate agreement based on cumulative emissions. Surround. Res. Lett. 10, 105004 (2015). The hybrid combination of equity approaches does not represent a fair operationalization of the CBDR-RC principle, in which all countries seek to maximize absolute profit31 by agreeing on a common approach to equity. Rather, it reflects national relative profit preferences32 – that is, a country`s propensity to measure the equity of its contribution to global mitigation efforts by looking at the efforts of other countries – not just national indicators. Despite claims that justice discussions are irrelevant or dangerous in a post-Paris world, justice is fundamental to climate policy research33,34, and scientific analysis of equitable burden-sharing can have an impact on UNFCCC processes5. However, the lack of agreement on the unanimous operationalization of the CBDR-CR should not be used as an excuse for inaction3 and should not leave the international community without a measure that reflects current agreements to assess the ratification process. The multitude of equity concepts leads to a wide range of emission allocations for countries and regions35, which is sometimes used by non-experts as a margin of uncertainty. In a recent climate case, the District Court of The Hague36.37 ruled that the Dutch government should reduce emissions at least to the least ambitious end of the IPCC-AR4 recommended range for the Annex I group of countries by 2020 on the basis of multiple capital allocations from 16 studies38. The Court did not adopt a justice approach and ruled in favour of the minimum effort in accordance with international treaties in the light of generally accepted science.
While the increase in climate litigation against governments39 (climatecasechart.com/) may contribute to a tightening of the process, systematic court decisions that governments must follow the least ambitious goal of a margin of justice would not be enough to achieve the Paris Agreement. As a first step, this paper models such a bottom-up situation in which each country pursues the least ambitious of the five burden-sharing approaches representative of the IPCC`s quantified categories35. In a second step, it models the hybrid approach, which is in line with the current trade-off, where each country takes a fair approach to burden-sharing to determine its efforts, but cannot directly apply this approach to influence the efforts of other countries. .