A B S T R A C TThis paper presents the overview of the Shared Socioeconomic Pathways (SSPs) and their energy, land use, and emissions implications. The SSPs are part of a new scenario framework, established by the climate change research community in order to facilitate the integrated analysis of future climate impacts, vulnerabilities, adaptation, and mitigation. The pathways were developed over the last years as a joint community effort and describe plausible major global developments that together would lead in the future to different challenges for mitigation and adaptation to climate change. The SSPs are based on five narratives describing alternative socio-economic developments, including sustainable development, regional rivalry, inequality, fossil-fueled development, and middle-of-the-road development. The longterm demographic and economic projections of the SSPs depict a wide uncertainty range consistent with the scenario literature. A multi-model approach was used for the elaboration of the energy, land-use and the emissions trajectories of SSP-based scenarios. The baseline scenarios lead to global energy consumption of 400-1200 EJ in 2100, and feature vastly different land-use dynamics, ranging from a possible reduction in cropland area up to a massive expansion by more than 700 million hectares by 2100.

The 2015 Paris Agreement calls for countries to pursue efforts to limit global-mean temperature rise to 1.5 °C. The transition pathways that can meet such a target have not, however, been extensively explored. Here we describe scenarios that limit end-of-century radiative forcing to 1.9 W m −2 , and consequently restrict median warming in the year 2100 to below 1.5 °C. We use six integrated assessment models and a simple climate model, under different socioeconomic , technological and resource assumptions from five Shared Socioeconomic Pathways (SSPs). Some, but not all, SSPs are amenable to pathways to 1.5 °C. Successful 1.9 W m −2 scenarios are characterized by a rapid shift away from traditional fossil-fuel use towards large-scale lowcarbon energy supplies, reduced energy use, and carbon-dioxide removal. However, 1.9 W m −2 scenarios could not be achieved in several models under SSPs with strong inequalities, high baseline fossil-fuel use, or scattered short-term climate policy. Further research can help policy-makers to understand the real-world implications of these scenarios.

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Integrated assessment models can help quantifying the implications of international climate agreements and regional climate action. This paper reviews scenario results from model intercomparison projects to explore different possible outcomes of post 2020 climate negotiations, recently announced pledges and their relation to 2°C. We provide key information for all the major economies such as the year of emission peaking, the regional carbon budgets and emissions allowances. We highlight the distributional consequences of climate policies, and discuss the role of carbon markets for financing clean energy investments, and achieving efficiency and equity.So far, international climate policy has been ineffective in curbing the rise of global greenhouse-gas emissions. Still, ambitious climate targets such as the 2°C target require a phase-out of global emissions by the end of the century, and an active participation of all world regions in climate policy 1 . Given the many obstacles to global cooperative action on climate change, the question remains how diverse national climate policies can be coordinated and strengthened globally. Within the United Nations Framework Convention on Climate Change (UNFCCC), the Durban Platform for Enhanced 2 Action 2 provides an important platform for a post-2020 international climate agreement. It contains several innovative elements, most notably a focus on the major economies that goes beyond the traditional divide between Annex I and non-Annex I countries. The Durban platform calls for a new climate treaty to be agreed in 2015 and implemented as early as 2020. The recently announced USChina climate deal and the EU climate framework provide encouraging steps forwards, but aligning the incentives of the major emitters in pursuing stringent climate policies remains a challenge. In this paper, we aim at assessing the implications of post 2020 climate policies with specific reference to the major economies. We provide quantitative estimates of regional emission budgets, timing of emission peaking, and distribution of mitigation costs. We examine the role of carbon markets and different burden sharing schemes to alleviate distributional inequalities and finance the investment needs in low carbon mitigation technologies. In order to quantify these policy relevant variables, we resort to global models.Integrated assessment models (IAMs) are tools designed to investigate the implications of achieving climate and other objectives in an integrated and rigorous framework. They are numerical models that account for major interactions among energy, land-use, economic and climate systems. Model differ in the economic, technological and sectoral representation and in the way they are solved, with some models maximizing an inter-temporal objective function (such as economic activity) and others simulating a set of equilibria (see the SOM for individual model description and references to documentation). Models generate global long-term scenarios for a number of regions or countries that ca...