-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...

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Transportation accounts for a substantial share of CO2 emissions, and decarbonizing transport will be necessary to limit global warming to below 2°C. Due to persistent reliance on fossil fuels, it is posited that transport is more difficult to decarbonize than other sectors. We test this hypothesis by comparing long-term transport energy demand and emission projections for China, USA and the World from five large-scale energy-economy models with respect to three climate policies. We systematically analyze mitigation levers along the chain of causality from mobility to emissions, and discuss structural differences between mitigation in transport and non-transport sectors. We can confirm the hypothesis that transport is difficult to decarbonize with purely monetary signals when looking at the period before 2070. In the long run, however, the three global models achieve deep transport emission reductions by >90% through the use of advanced vehicle technologies and carbon-free primary energy; especially biomass with CCS plays a crucial role. Compared to the global models, the two partial-equilibrium models are relatively inflexible in their reaction to climate policies. Across all models, transportation mitigation lags behind non-transport mitigation by 10-30 years. The extent to which earlier mitigation is possible strongly depends on implemented technologies and model structure.

The projections of 89 scenarios from 12 different models for the CO 2 emissions of China to 2030 are reviewed, along with wider examinations of lessons from the history of energy forecasting in OECD countries, and of the Chinese macroeconomic situation.Even by 2030, emissions in the scenarios span a factor of almost 2.5, indicating significant range and uncertainty. Statistical analysis of Kaya components suggests the carbon intensity of energy supply to be the strongest determining factor. However, most scenarios assume that industry 1 continues to account for more than 50% of total final energy demand. This is in contrast both to historical examples, which have consistently shown economies shifting from energy-intensive industrial bases to servicebased structures as income per capita rises, and to recent Chinese policy statements, which reflect a similar ambition. It is also highly salient that major failures in energy and emissions projections can frequently be accounted for in retrospect by failures to anticipate such major economic structural shifts.In conclusion, while the future trajectory of Chinese emissions remains profoundly uncertain, the potential for a significant Chinese macroeconomic transition and its implications for the scale and structure of energy demand will be a crucial factor, to which energy-climate models must pay far more attention. Policy relevanceThe dramatic growth of Chinese emissions since 2000 has become a major factor in global emission prospects and the international political agenda. Many models project rapid continued emissions growth, but an apparent halt in Chinese emissions in 2014 has amplified debate. Projections and policy need to recognise fundamental uncertainties in emission prospects, because in addition to energy/climate-specific policies, they depend on the progress in Chinese macroeconomic reforms, which are poorly represented in the models we survey. Global projections, the international process, and the design of China's own policies (most obviously, its national cap-and-trade system) need to cope with the possibility of continued growth to peaking in 2030 (the central commitment in China's Intended Nationally Determined Contribution), but must also be prepared to exploit and encourage the possibilities of low-carbon development and much earlier peaking.

In order to mobilize the volume of mitigation required to reach a global emissions path consistent with 1.5°C, policy instruments need to be much more stringent than they have been to date. They will have to ensure full decarbonization of key economic sectors within one generation, which will require retirement of high-carbon assets before the end of their technical lifetime. However, political economy shows that only those instruments will be implemented that benefit well-organized interest groups while spreading costs as widely as possible. In the past, this has led to distortions such as emissions trading systems with systemic overallocation of allowances, or carbon taxes that exempt industry. Under favourable lobbying constellations strong subsidy schemes for mitigation can emerge. Renewable feed-in tariffs in Europe persisted for over two decades and were crucial for the breakthrough of wind and solar power technologies. But once competition from China led to the demise of European technology providers and the European population started to feel the pinch from the surcharges on their electricity bills, feed-in tariffs were abolished. Historically, rapid transformations of the nature required to reach 1.5°C built on either lavish public investment into the underlying infrastructure or a general notion of national emergency. Innovative forms of market mechanisms could convince policy makers that mitigation costs are lower than expected and thus accelerate mitigation. For the long-term success of far-reaching mitigation policies, it will be crucial whether they can be framed as harnessing an opportunity or whether they are seen as a grim, but grudgingly accepted response to a societal emergency. Key policy insights. Interest groups play a key role in the design of mitigation policy instruments and reduce their efficiency as well as effectiveness.. Instruments generating high carbon price levels may in the future be possible if redistribution of revenues is done in a way that soothes the key interest groups.. A mixture of market mechanisms for mobilization of mature mitigation technologies with a dedicated public investment programme for emerging technologies seems promising, provided technologies can be 'weaned off' public support at the right point in time.. For contentious, 'emergency' technologies such as Negative Emission Technologies (NETs) or Solar Radiation Management (SRM), governance mechanisms on the international level are critical.