-a new global agreement to combat climate change-was adopted under the United Nations Framework Convention on Climate Change (UNFCCC). In preparation of this agreement, countries submitted national plans that spell out their intentions for addressing the climate change challenge after 2020 2 . These Intended Nationally Determined Contributions (INDCs) address a range of issues, which can relate to avoiding, adapting or coping with climate change, among other things. Nevertheless, targets and actions for reducing greenhouse gas (GHG) emissions are core components. At this point, the INDCs are not final and can be modified up until the time the Paris Agreement is ratified. However, for now they represent our best understanding of the climate actions countries intend to pursue after 2020.The overarching climate goal of the Paris Agreement is to hold "the increase in the global average temperature to well below 2 °C above preindustrial levels and to pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels" 1 . This climate goal represents the level of climate change that governments agree would prevent dangerous interference with the climate system, while ensuring sustainable food production and economic development 3,4 , and is the result of international discussions over multiple decades 5 . Limiting warming to any level implies that the total amount of carbon dioxide (CO 2 ) that can ever be emitted into the atmosphere is finite 6 . From a geophysical perspective, global CO 2 emissions thus need to become net zero 7,8 . About two thirds of the available budget for keeping warming to below 2 °C have already been emitted [9][10][11] , and increasing trends in CO 2 emissions 12 indicate that global emissions urgently need to start to decline so as to not foreclose the possibility of holding warming to well below 2 °C (refs 13, 14). The window for limiting warming to below 1.5 °C with high probability and without temporarily exceeding that level already seems to have closed 15 . The Paris Agreement implicitly acknowledges these insights and aims to reach a global peak in GHG emissions as soon as possible together with achieving "a balance" between anthropogenic emissions and removals of GHGs in the second half of this century. Both targets are in principle consistent with the temperature objective of the Agreement 16,17 , but beg the broader question of whether current INDCs are already putting the world on a path towards achieving them.Besides the climate question, the first round of INDCs also raises many other issues. These include whether efforts are distributed equitably among countries; how much adaptation may be required given the current level of mitigation ambition; how 'intended' national proposals will be implemented; how they will be financed; and the extent to which the INDCs contribute to the achievement of other goals of the UNFCCC by building on institutions that can support adaptation to climate change, technology advancement, development path transformation, sustainable...

Many countries have implemented national climate policies to accomplish pledged Nationally Determined Contributions and to contribute to the temperature objectives of the Paris Agreement on climate change. In 2023, the global stocktake will assess the combined effort of countries. Here, based on a public policy database and a multi-model scenario analysis, we show that implementation of current policies leaves a median emission gap of 22.4 to 28.2 GtCO 2 eq by 2030 with the optimal pathways to implement the well below 2°C and 1.5°C Paris goals. If Nationally Determined Contributions would be fully implemented, this gap would be reduced by a third. Interestingly, the countries evaluated were found to not achieve their pledged contributions with implemented policies (implementation gap), or to have an ambition gap with optimal pathways towards well below 2°C. This shows that all countries would need to accelerate the implementation of policies for renewable technologies, while efficiency improvements are especially important in emerging countries and fossilfuel-dependent countries.

As countries negotiate a new climate agreement for the United Nations climate conference in December 2015, a groundswell of climate actions is emerging as cities, regions, businesses and civil society groups act on mitigation and adaptation, independently, with each other and with national governments and international organizations. The Paris conference provides a historic opportunity to establish a framework to catalyse, support, and steer these initiatives. Without such a framework, 'bottom-up' climate governance runs the risk of failing to deliver meaningful results. Social science research highlights the need for a comprehensive approach that promotes ambition, experimentation and accountability, and avoids unnecessary overlaps. This article specifies functions and design principles for a new, comprehensive framework for sub-and nonstate climate actions that could provide effective coordination.