Mikiko Kainuma

The next generation of scenarios for climate change research and assessment

Advances in the science and observation of climate change are providing a clearer understanding of the inherent variability of Earth’s climate system and its likely response to human and natural influences. The implications of climate change for the environment and society will depend not only on the response of the Earth system to changes in radiative forcings, but also on how humankind responds through changes in technology, economies, lifestyle and policy. Extensive uncertainties exist in future forcings of and responses to climate change, necessitating the use of scenarios of the future to explore the potential consequences of different response options. To date, such scenarios have not adequately examined crucial possibilities, such as climate change mitigation and adaptation, and have relied on research processes that slowed the exchange of information among physical, biological and social scientists. Here we describe a new process for creating plausible scenarios to investigate some of the most challenging and important questions about climate change confronting the global community.

Scenario analysis of global warming using the Asian Pacific Integrated Model (AIM)

Abstract The Asian Pacific Integrated Model (AIM) is a large-scale model for scenario analyses of green-house gas (GHG) emissions and the impacts of global warming in the Asian Pacific region. The AIM comprises two main models — the AIM/emission model for predicting GHG emissions and the AIM/impact model for estimating the impacts of global warming — which are linked by the global GHG cycle and the climate change models. This paper categorizes the scenarios that have been written so far in relation to global warming, and then, given fixed inputs, simulates the effects of global warming taking into account various uncertainties. Several recent outcomes from the AIM/impact model are then described. Assuming climate change scenarios deduced from AIM/emission and GCM experiments, primary impacts on water resources and natural vegetation are assessed.

Assessment of emissions scenarios revisited

This article assesses emissions scenarios in the literature, originally documented in the scenario database that was developed more than 7 years ago. The original scenario assessment and literature review has been used, among other things, as the basis for the quantification of the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) reference scenarios and the IPCC Third Assessment Report (TAR) stabilization scenarios. In the meantime, a large number of new emissions scenarios have been developed and published. We have collected the relevant information about these new scenarios with the objective to assess the more recent perspectives about future global emissions and to assess the changes in the perspectives about future emissions and their driving forces that may have occurred since the publication of SRES and TAR scenarios. Our analysis goes beyond mere comparisons of emissions ranges. In particular, we explore the underlying drivers of emissions using the so-called IPAT identity (Impacts are proportional to the product of Population, Affluence, and Technology). When IPAT analysis refers to carbon emissions it is called the Kaya identity, where carbon dioxide (CO2) emissions are assumed to correspond to the product of population, per capita income, energy intensity of gross domestic product (GDP), and CO2 intensity of energy. Comparing the recent scenario literature with the scenarios developed before TAR shows that there are strong similarities for the main underlying tendencies in many of the scenario’s driving forces and results.

The AIM/end-use model and its application to forecast Japanese carbon dioxide emissions

Abstract The Asian-Pacific Integrated Model (AIM) has been developed for predicting greenhouse gas emissions and evaluating policy measures to reduce them. Two socioeconomic scenarios were assumed and CO 2 emissions were predicted based on these scenarios and policy intervention assumptions. It is found that mitigating CO 2 emissions by 6% to the 1990 level is possible without scaling back productive activities or living standards in Japan. However, this cannot be achieved by relying on the market mechanism alone. Our analysis shows that it is indispensable to introduce new policies and measures such as a carbon tax and subsidies.

Back-casting analysis for 70% emission reduction in Japan by 2050

This article envisions a future in which advances in technology and urban development have transformed Japanese society by 2050, resulting in significant greenhouse gas reductions. Pathways leading Japan towards a low-carbon society are calculated using a scenario approach based on ‘back-casting’ techniques. It is possible to reach a 70% reduction in CO2 emissions through a combination of demand-side and supply-side actions. On the demand side, reductions of 40–45% are possible through efficiency improvements, decreased population and the more rational use of energy despite increased energy demands arising in certain sectors. On the supply side, CO2 emissions can be reduced through a combination of the appropriate choice of low-carbon energy sources (including carbon capture and storage) and improving energy efficiency. The estimated direct annual cost of technology to achieve this by 2050 is 6.7–9.8 trillion yen, approximately 1% of the estimated 2050 GDP. However, this excludes costs involved in infrastructure investments with aims other than climate policy (e.g. strengthening international competitiveness, improving security, enhancing urban development, and reinforcing energy). To avoid investing in its current high-carbon-emitting infrastructure, Japan must develop long-term strategies to create the necessary technological and societal innovations and to channel the appropriate financial resources for intensive economy-wide change, such as development of land, urban areas, and buildings, improvements in industrial structures, and new technologies.

Estimation of embodied CO2 emissions by general equilibrium model

Abstract This study estimates the extent to which embodied CO2 emissions are increased or reduced when a socioeconomic structural change occurs. Embodied CO2 emissions were estimated by Input–Output models (I–O models) and a General Equilibrium model (GE model), and the respective results were compared. The embodied CO2 emissions differ greatly depending on the assumptions of the total system. The embodied CO2 emissions obtained by I–O models are much larger than those obtained by the GE model. In some cases, the total CO2 emissions increase even if less intermediate inputs are required owing to technological improvement. It is shown that taking I–O type embodied emissions alone into consideration is insufficient for the estimation of policy effects. Careful consideration is necessary to effectively reduce emissions when production and consumption are interconnected in a complex way.

Development of an end-use model for analyzing policy options to reduce greenhouse gas emissions

An end-use energy model is presented for assessing policy options to reduce greenhouse gas emissions. This model evaluates the effects of imposing a carbon tax on various carbon-emitting technologies in order to reduce CO/sub 2/ emissions. It also estimates the effects of a carbon tax in combination with subsidies. The problem can be formulated in terms of two-level mathematical programming. An algorithm is proposed and applied to estimate Japanese CO/sub 2/ emissions. The conditions under which energy-saving technologies would be selected are analyzed using various carbon tax rates and subsidies, and the reduction of CO/sub 2/ emissions is calculated based on the introduction of such technologies. It is found that a low carbon tax such as 3000 yen per metric ton of carbon (tC) is insufficient to stabilize CO/sub 2/ emissions at the 1990 level in Japan, and that a tax of 30000 yen/tC would be necessary. However, the proposed algorithm shows that total emissions in Japan in the year 2000 can be stabilized at the 1990 level with a tax of 3000 yen/tC if the tax revenues are used to subsidize the introduction of energy-saving technologies.

A low-carbon society: global visions, pathways, and challenges

The feasibility of two low-carbon society (LCS) scenarios, one with and one without nuclear power and carbon capture and storage (CCS), is evaluated using the AIM/Enduse[Global] model. Both scenarios suggest that achieving a 50% emissions reduction target (relative to 1990 levels) by 2050 is technically feasible if locally suited technologies are introduced and the relevant policies, including necessary financial transfers, are appropriately implemented. In the scenario that includes nuclear and CCS options, it will be vital to consider the risks and acceptance of these technologies. In the scenario without these technologies, the challenge will be how to reduce energy service demand. In both scenarios, the estimated investment costs will be higher in non-Annex I countries than in Annex I countries. Finally, the enhancement of capacity building to support the deployment of locally suited technologies will be central to achieving an LCS. Policy relevance Policies to reduce GHG emissions up to 2050 are critical if the long-term target of stabilizing the climate is to be achieved. From a policy perspective, the cost and social acceptability of the policy used to reduce emissions are two of the key factors in determining the optimal pathways to achieve this. However, the nuclear accident at Fukushima highlighted the risk of depending on large-scale technologies for the provision of energy and has led to a backlash against the use of nuclear technology. It is found that if nuclear and CCS are used it will be technically feasible to halve GHG emissions by 2050, although very costly. However, although the cost of halving emissions will be about the same if neither nuclear nor CCS is used, a 50% reduction in emissions reduction will not be achievable unless the demand for energy service is substantially reduced.

Emissions scenarios database and regional mitigation analysis: a review of post-TAR mitigation scenarios

The objectives of this study were to carry out a review of mitigation scenarios that have emerged since the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR), to update the current Emissions Scenarios Database with these scenarios, and to analyze emissions and mitigation scenarios. This article first discusses the characterization of mitigation scenarios and systematically classifies mitigation scenarios. Second, quantitative analyses on gross domestic product (GDP), population, carbon intensity, energy intensity, and carbon taxes are conducted at the regional level in the four regional aggregations used by the IPCC Special Report on Emissions Scenarios. Results show that the range of emissions trajectories is extensive and that the maximum potential mitigation of global CO2 emissions from the baseline level by 2100 is around 95%. There is a correlation between GDP growth and energy intensity improvement. The relationship between energy intensity improvement and carbon intensity reduction changes over the 21st century, with energy intensity improvement outweighing carbon intensity reduction in the first half of the century and carbon intensity reduction becoming more dominant in the latter half. Predicted carbon tax levels for 2100 range from around 50 to 1400 US

Assessing decarbonization pathways and their implications for energy security policies in Japan

/t-C, although a uniform level of carbon tax brings about widely varying CO2 mitigation outcomes across different regions. The range of GDP loss, resulting from CO2 emissions mitigation, varies from −10% to 40% in 2100, with GDP losses in developing regions more evident than those in developed regions.