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Energy and climate policies may have significant economy-wide impacts, which are regularly assessed based on quantitative energy-environment-economy models. These tend to vary in their conclusions on the scale and direction of the likely macroeconomic impacts of a low-carbon transition. This paper traces the characteristic discrepancies in models' outcomes to their origins in different macro-economic theories, most importantly their treatment of technological innovation and finance. We comprehensively analyse the relevant branches of macro-innovation theory and group them into two classes: 'Equilibrium' and 'Non-equilibrium'. While both approaches are rigorous and self-consistent, they frequently yield opposite conclusions for the economic impacts of low-carbon policies. We show that model outcomes are mainly determined by their representations of monetary and finance dimensions, and their interactions with investment, innovation and technological change. Improving these in all modelling approaches is crucial for strengthening the evidence base for policy making and gaining a more consistent picture of the macroeconomic impacts of achieving emissions reductions objectives. The paper contributes towards the ongoing effort of enhancing the transparency and understanding of sophisticated model mechanisms applied to energy and climate policy analysis. It helps tackle the overall 'black box' critique, much-cited in policy circles and elsewhere. Key policy insights Quantitative models commissioned by policy-makers to assess the macroeconomic impacts of climate policy generate contradictory outcomes and interpretations. The source of the differences in model outcomes originates primarily from assumptions on the workings of the financial sector and the nature of money, and of how these interact with processes of low-carbon energy innovation and technological change. Representations of innovation and technological change are incomplete in energy-economy-environment models, leading to limitations in the assessment of the impacts of climate-related policies. All modelling studies should state clearly their underpinning theoretical school and their treatment of finance and innovation. A strong recommendation is given for modellers of energy-economy systems to improve their representations of money and finance. [ABSTRACT FROM AUTHOR]

This article assesses the feasibility of a 50% reduction in CO2 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/tCO2 by 2050, attained through auctioned CO2 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 CO2 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/tCO2 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. [ABSTRACT FROM AUTHOR]