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This article analyses the implications of long-term low-carbon scenarios for the UK, and against these it assesses both the current status and the required scope of the UK energy policy. The scenarios are generated using the well-established MARKAL (acronym for MARKet ALlocation) UK energy systems model, which has already been extensively used for UK policy analysis and support. The scenarios incorporate different levels of ambition for carbon reduction, ranging from 40% to 90% cuts from 1990's level by the year 2050, to shed insights into the options for achieving the UK's current legally binding target of an 80% cut by the same date. The scenarios achieve their carbon reductions through very different combinations of demand reduction (implying behaviour change) and implementation of low-carbon and energy efficiency technologies on both the supply and demand sides. In all cases, however, the costs of achieving the reductions are relatively modest. The ensuing policy analysis suggests that while the cuts are feasible both technically and economically and while a number of new policies have been introduced in order to achieve them, it is not yet clear whether these policies will deliver the required combination of both short- and long-term technology deployment, and behaviour change for the UK Government's targets to be achieved.

Low-carbon society scenarios visualize social, economic and technological transitions through which societies respond to climate change. This article assesses two paradigms for transiting to a low-carbon future in India. An integrated modelling framework is used for delineating and assessing the alternative development pathways having equal cumulative CO 2 emissions during the first half of the 21st century. The first pathway assumes a conventional development pattern together with a carbon price that aligns India's emissions to an optimal 550 ppmv CO 2 e stabilization global response. The second emissions pathway assumes an underlying sustainable development pattern characterized by diverse response measures typical of the 'sustainability' paradigm. A comparative analysis of the alternative development strategies is presented on multiple indicators such as energy security, air quality, technology stocks and adaptive capacity, and conclusions are drawn.

If dangerous climatic change is to be avoided, all countries will need to contribute to reductions in greenhouse gas emissions on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities. This article discusses the gap between the past (ideal) model analysis for emission reductions and realistic policies. A key requirement for successful policies is their acceptance by as many countries as possible and their ease of practical implementation. The sectoral intensity approach has been proposed for its focus on tangible, practical actions; however, its emission reduction effects have been said to be ambiguous and difficult to evaluate quantitatively. The effects of global emission reduction based upon a sectoral approach to energy and carbon intensity targets are evaluated using an energy systems model with a high regional resolution and a detailed description of technology. This analysis found that deep emission cuts can be achieved by a sectoral approach, provided that developed and developing countries collaborate towards emission cuts under the proposed framework. This framework has a higher potential for agreement by both developed and developing countries.

At the recent UN climate negotiations in Bali, most countries sought an agreement to cut industrialized countries' emissions of CO 2 by between 25% and 40% by 2020. The final agreed wording at Bali was that 'deep cuts' in emissions were required, without further quantification. The PAGE2002 probabilistic integrated assessment model is deployed to investigate how deep those deep cuts should be. We calculate optimal CO 2 emissions over time under uncertainty using the same assumptions and assessment model as in the Stern Review, where optimal emissions are those which minimize the mean net present value of the sum of climate change impacts and adaptation and abatement costs. The optimal global CO 2 emissions under these assumptions require much deeper cuts, of 55% by 2020 and 75% by 2060 compared with emissions in 2000. If the Stern Review is to be believed, emissions cuts of 25-40% by 2020 will be insufficient to achieve global climate objectives.

The Low-Carbon Society (LCS) research project (Strachan et al., 2008a) is examined for its insights about the scale, nature and timing of the deployment of low-carbon technologies. In addition to 'carbon price only' policies, other incentives and demand-side efforts are needed in order to embed climate policies into broader development approaches. The question of what constitutes transition pathways is considered. Fundamental institutional, individual and social changes are needed to accompany economic and technological change as energy is embedded in overall development patterns. The cost assessment of decarbonization policies may be too optimistic if it is only considered as the final outcome of a LCS, and if the inevitable hindrances and setbacks along the transition pathway are disregarded. The significance of transition costs is highlighted, together with their causes: social and short- and medium-term economic costs and adjustments in macroeconomic dynamics. Although the overall welfare costs of LCS are likely to be smaller than the benefits (including the co-benefits), a clear and realistic understanding of potential transition difficulties is necessary in order to define the robust policy mix needed to underpin it.

The challenge of creating a global low-carbon society is examined from the perspectives of a slow-growing but highly developed economy (Canada) and a fast-growing developing economy (China). Both countries' responses are compared to a similar carbon price schedule (US$10/tCO 2 e in 2013 rising exponentially to $100 by 2050) using a hybrid technologically explicit and behaviourally realistic model with macroeconomic feedbacks (CIMS). Then additional measures are imposed based on the national circumstances of each country; for Canada we simulate a 50% reduction by 2050, and stabilization for China. The scale of the challenge in all cases requires that every available option be vigorously pursued, including energy efficiency, fuel switching, carbon capture and storage, and accelerated development of renewables; to compensate, there are significant co-reductions of local air pollutants such as SO x and NO x . Finally, the abatement cost schedules of China and Canada are compared, and implications considered for carbon permit flows if the cost schedule of the rest of the developed world is assumed to be similar to that of Canada. We found that the developed world and China could collectively reduce emissions by 50% in 2050 at a price of $175/tCO 2 e, with permits flowing from the developed countries to China; while abatement costs are lower in China up to $75/t, at higher prices reductions are less costly in the developed world. Our results indicate that a global low-carbon society is feasible, on condition that policy makers are willing and able to impose long-term, credible policy packages with carbon pricing policy as the core element, coupled with supplementary regulations to address market failures.

The Low-Carbon Society (LCS) research project (Strachan et al., 2008) is to be congratulated for providing a rich, useful source of models to inform and precipitate discussion of policy options for moving towards a low-carbon society. This commentary explores additional considerations that warrant inclusion in any policy discussion: the feasibility of political will and leadership, the limitations of technical feasibility, and clarity about what 'the price of carbon' means. Difficulties exist with establishing carbon prices due to differences in energy prices between countries and the distinction between baseline (existing policies) and additional parts. An alternative may be to place more emphasis on the energy price for mitigation, along with other indicators (energy efficiency, carbon intensity, renewable power diffusion) for comparison. A policy is proposed, based on the energy price combined with an emphasis on accelerating technological innovation and overcoming barriers to the adoption of energy efficiency measures.

This article assesses the feasibility of a 50% reduction in CO 2 emissions by 2050 using a large-scale Post Keynesian simulation model of the global energy-environment-economy system. The main policy to achieve the target is a carbon price rising to $100/tCO 2 by 2050, attained through auctioned CO 2 permits for the energy sector, and carbon taxes for the rest of the economy. This policy induces technological change. However, this price is insufficient, and global CO 2 would be only about 15% below 2000 levels by 2050. In order to achieve the target, additional policies have been modelled in a portfolio, with the auction and tax revenues partly recycled to support investment in low-GHG technologies in energy, manufacturing and transportation, and 'no-regrets' options for buildings. This direct support supplements the effects of the increases in carbon prices, so that the accelerated adoption of new technologies leads to lower unit costs. In addition the $100/tCO 2 price is reached earlier, by 2030, strengthening the price signal. In a low-carbon society, as modelled, GDP is slightly above the baseline as a consequence of more rapid development induced by more investment and increased technological change.

An integrated set of low-carbon society (LCS) scenarios for the UK were analysed using the UK MARKAL Macro (M-M) model. A $100/tCO 2 carbon price scenario was compared with long-term LCS scenarios with a domestic 80% CO 2 reduction target. As M-M is a national-level model, a set of five international drivers were investigated, and grouped under Annex I consensus and Global consensus assumption sets. For economy-wide results the inclusion of international aviation and potential large-scale purchases of CO 2 permits (when available) are most important. For sectoral implications, all international drivers considered here are important; for example in divergent overall size and configuration of the UK electricity sector. The carbon price scenario and set of 80% LCS targets scenarios give GDP losses rising from 0.36% to a range of 1.64-2.21% in 2050. This steep cost convexity in deep CO 2 reductions represents increasing efforts to decarbonize the UK energy system, and the further impact of key international drivers. This illustrative analysis demonstrates that UK policy makers should be cognisant of, and flexible with respect to, international strategies on LCS and emission reduction targets.

Under the Japan-UK research project 'Low-Carbon Society (LCS) Scenarios Towards 2050', an international modelling comparison was undertaken by nine national teams, with a strong developing-country focus. Core model runs were a Base case, a Carbon price case (rising to $100/tCO 2 by 2050) and a Carbon-plus case to investigate an LCS scenario with a 50% reduction in global CO 2 emissions by 2050. The comparison emphasis was to focus on individual model strengths (notably technological change, international emissions trading, non-price (sustainable development) mechanisms and behavioural change) rather than a common integrated assumption set. A complex picture of long-term LCS scenarios comes from the range of model types and geographical scale (global vs. national); however, common themes for policy makers do emerge. A core finding is that LCS scenarios are technologically feasible. However, preferred pathways require clear and early target setting and incorporation of emissions targets across all economic activities. This will probably entail significant socio-economic changes. To realize major LCS transitions requires sustained progress in R&D and deployment of a broad range of technologies, with carbon capture and storage (CCS) a key technology in most low-carbon portfolios. Developing countries, in particular, face an immense challenge to achieve LCS in light of their economic growth requirements. As such, international cooperation is required in iterative and flexible burden sharing under international emissions trading regimes.