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How can dangerous interference with the climate system be avoided? Science can help decision-makers answer this political question. Earlier publications have focused on the probability of keeping global mean temperature change below certain thresholds by stabilizing greenhouse gas concentrations at particular levels. We compare the results of such "stabilization profiles" with a set of "peaking profiles" that reduce emissions further after stabilization and thus result in a concentration peak. Given the inertia in the climate system, stabilization profiles lead to ongoing warming beyond 2100 until the temperature reaches equilibrium. This warming partly can be prevented for peaking profiles. In this way, these profiles can increase the likelihood of achieving temperature thresholds by 10–20% compared with the likelihood for the associated stabilization profiles. Because the additional mitigation efforts and thus costs for peaking profiles lie mainly beyond 2100, peaking profiles achieving temperature thresholds with the same likelihood as the original stabilization profile, but at considerably lower cost (up to 40%), can be identified. The magnitude of the cost reductions depends on the assumptions on discounting. Peaking profiles and overshoot profiles with a limited overshoot may, in particular, play an important role in making more ambitious climate targets feasible.

A post-2012 regime aimed at reducing greenhouse gas (GHG) emissions could develop towards a universal or fragmented regime. The fundamental difference between a universal and a fragmented regime is that the first involves a single comprehensive climate regime in which all countries participate, whereas the second involves either multiple treaties or a single treaty in which not all countries participate. This study assesses the literature on a wide range of different model studies concerning the environmental effectiveness and economic consequences of various universal and fragmented climate regimes. The most important conclusions (e.g. relative position of regions in terms of costs) are generally consistent across different studies, despite the differences in methodology. We conclude that stabilising GHG concentrations at low levels is more costly with a fragmented regime than with a universal regime, because reduction targets must be achieved by a smaller number of countries or because fragmented treaties may prevent reducing GHGs where it is cheapest to do so. However, establishing a universal regime will be challenging due to cost differences between regions if emissions are allocated based on specific allocation rules and incentives to free-ride on a universal regime. Even though alternative behaviours such as responsibility, the implementation of transfer schemes or exclusive membership can increase the likelihood of achieving a universal regime, a fragmented regime seems more feasible. Therefore, a transitional fragmented 'coalition of the willing' could be established first, which could provide the basis for a larger, universal regime in the long term. Adapted from the source document.

The planetary boundaries (PBs) framework proposes global quantitative precautionary limits for human perturbation of nine critical Earth system processes. Together they define a global safe operating space for human development. Translating the global limits to the national level increases their policy relevance. Such translation essentially divides up the global safe operating space. What is considered fair distribution is a political decision and there is no globally agreed principle that can be applied. Here, we analyse the distributional consequences of alternative perspectives on distributive fairness. We scale the global limits of selected PBs to resource budgets for the EU, US, China and India, using three allocation approaches from the climate change literature. Furthermore, we compare the allocated budgets to 2010 environmental footprints of the four economies, to assess their performance with respect to the selected PBs. The allocation approaches are based on (1) current shares of global environmental pressure ('grandfathering'); (2) 'equal per capita' shares, and (3) 'ability to pay' to reduce environmental pressure. The results show that the four economies are not living within the global safe operating space. Their 2010 environmental footprints are larger than the allocated budgets for all approaches and parameterisations analysed for the PBs for climate change and biogeochemical flows, and, except for India, also for the PB for biosphere integrity. Grandfathering was found to be most favourable for the EU and US for all PBs, and ability to pay as least favourable. For climate change and biogeochemical flows, ability to pay even resulted in negative resource budgets for the two economies. In contrast, for China and India, equal per capita allocation and ability to pay were most favourable. Results were sensitive to the parameterisation. Accounting for future population growth in the equal per capita approach benefits India, with lower budgets for the EU, US and China, while accounting for future ...

Sub-Saharan Africa faces several challenges that hamper the effort to provide universal electricity access. The challenges are not the result of lack of energy resources but rather the result of governance and institutional problems as well as lack of capital to meet the high investment requirement. This study aims to provide relevant policy recommendations to facilitate the path towards universal electricity access in Sub-Saharan Africa. We do this by identifying the barriers for electricity access and the relevant actors, institutions, and regulations using desk research, stakeholder interviews and expert workshops. The results show that the absence of overall plans and approaches and lack of clarity in policies are the main challenges for the sector. Setting standards for electricity products, such as solar panels, could help to reduce the problem of counterfeit poor quality products. A broader participation of non-governmental actors is needed to increase the speed of electrification. This requires innovative revenue schemes, financial and fiscal incentives and elimination of market distortions. More generally, we conclude that stable and consistent policy frameworks and improved coordination between actors, are crucial to accelerate electrification in the region.

In the Paris Agreement under the United Nations Framework Convention on Climate Change (UNFCCC), for the first time, non-state actors were addressed in the international negotiations and were explicitly invited to act on climate change. Indeed, there are many transnational emission reduction initiatives (TERIs) outside the UNFCCC, driven by non-state actors or national governments, which aim at reducing greenhouse gas (GHG) emissions. Using an Integrated Assessment Model (IAM), this study assessed the potential impact of a selection of large TERIs that existed before the Paris Agreement on global greenhouse gas emissions. TERIs could lead to significant emission reductions: the eleven selected initiatives included in the analysis here could – if fully implemented – deliver annual GHG emission reductions of 2.5 GtCO2eq by 2020 and of 5.0 GtCO2eq by 2030 from a no-policy-baseline emission level of 53.7 GtCO2 and 61.1 GtCO2eq, respectively. Although these reductions are of similar magnitude as those pledged by countries under the umbrella of the UNFCCC, these reductions may significantly overlap with those of pledges and Nationally Determined Contributions. The maximum estimate of overlap is around 70% by 2020 and 80% by 2030. This means that the combined impact on global GHG emissions of TERIs and NDCs, assuming a maximum overlap, would lead to emission levels between 53 and 55 GtCO2eq by 2030, compared to a level of 54 to 56 GtCO2eq resulting from NDCs alone.

The planetary boundaries framework proposes quantitative global limits to the anthropogenic perturbation of crucial Earth system processes, and thus marks out a planetary safe operating space for human activities. Yet, decisions regarding resource use and emissions are mostly made at less aggregated scales, by national and sub-national governments, businesses, and other local actors. To operationalize the planetary boundaries concept, the boundaries need to be translated into and aligned with targets that are relevant at these decision-making scales. In this paper, we develop a framework that addresses the biophysical, socio-economic, and ethical dimensions of bridging across scales, to provide a consistently applicable approach for translating the planetary boundaries into national-level fair shares of Earth's safe operating space. We discuss our findings in the context of previous studies and their implications for future analyses and policymaking. In this way, we link the planetary boundaries framework to widely-applied operational and policy concepts for more robust strong sustainability decision-making.

The planetary boundaries framework proposes quantitative global limits to the anthropogenic perturbation of crucial Earth system processes, and thus marks out a planetary safe operating space for human activities. Yet, decisions regarding resource use and emissions are mostly made at less aggregated scales, by national and sub-national governments, businesses, and other local actors. To operationalize the planetary boundaries concept, the boundaries need to be translated into and aligned with targets that are relevant at these decision-making scales. In this paper, we develop a framework that addresses the biophysical, socio-economic, and ethical dimensions of bridging across scales, to provide a consistently applicable approach for translating the planetary boundaries into national-level fair shares of Earth's safe operating space. We discuss our findings in the context of previous studies and their implications for future analyses and policymaking. In this way, we link the planetary boundaries framework to widely-applied operational and policy concepts for more robust strong sustainability decision-making.