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Restraining global average temperatures to +2°C from pre-industrial levels will likely require halving global energy system emissions by 2050, and decarbonization by 2100 (IPCC 2014). In the nationally orientated climate policy framework codified under the Paris Agreement, each nation must decide the scale and method of their emissions reduction contribution while remaining consistent with the global carbon budget. This policy process will require engagement amongst a wide range of stakeholders who have very different visions for the physical implementation of deep decarbonization. The Deep Decarbonization Pathways Project (DDPP) has developed a methodology, building on the energy, climate, and economics literatures, to structure these debates based on the following principles: i) country scale analysis to capture specific physical, economic, and political circumstances to maximize policy relevence, ii) a long-term perspective to harmonize shortterm decisions with the long term objective, and iii) detailed sectoral analysis with transparent representation of emissions drivers through a common accounting framework. These principles are operationalized in the definition of Deep Decarbonization Pathways (DDPs), which involve technically detailed, sector by sector maps of each country's decarbonization transition, backcasting feasible pathways from 2050 end points. This paper shows how the current 16 DDPP country teams, covering 74% of global energy system emissions, used this method to collectively restrain emissions to a level consistent with +2°C while maintaining development aspirations and reflecting national circumstances, mainly through efficiency, decarbonization of energy carriers (e.g. electricity), and switching to these carriers. The cross-cutting analysis of country scenarios reveals important enabling conditions for the transformation, pertaining to technology R&D, investment, trade and global and national policies.

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The Paris Agreement introduces long-term strategies as an instrument to inform progressively more ambitious emission reduction objectives, whilst holding development goals paramount in context of national circumstances. In the lead up to COP21, the Deep Decarbonization Pathways Project developed mid-century low-emission pathways for 16 countries, based on an innovative pathway design framework. In this Perspective we describe this framework and show how it can support the development of sectorally and technologically detailed and policy-relevant country-driven strategies consistent with the Paris Agreement climate goal. We also discuss how this framework can be used to engage stakeholder input and buy-in; design implementation policy packages; reveal necessary technological, financial and institutional enabling conditions; and support global stocktaking and ratcheting of ambition.