Takashi Homma

Global emission reductions through a sectoral intensity target scheme

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.

Analysis of Technological Portfolios for CO2 stabilizations and Effects of Technological Changes

In this study, cost-effective technological options to stabilize CO2 concentrations at 550, 500, and 450 ppmv are evaluated using a world energy systems model of linear programming with a high regional resolution. This model treats technological change endogenously for wind power, photovoltaics, and fuel-cell vehicles, which are technologies of mass production and are considered to follow the learning by doing process. Technological changes induced by climate policies are evaluated by maintaining the technological changes at the levels of the base case wherein there is no climate policy. The results achieved through model analyses include 1) cost-effective technological portfolios, including carbon capture and storage, marginal CO2 reduction costs, and increases in energy system cost for three levels of stabilization and 2) the effect of the induced technological change on the above mentioned factors. A sensitivity analysis is conducted with respect to the learning rate.

Role of CO2 sequestration by country for global warming mitigation after 2013

Publisher Summary This chapter evaluates CO2 sequestration technologies in parallel with other mitigation technologies and also in consideration of their regional differences. Five kinds of CO 2 sequestration technologies are modeled: enhanced oil recovery, depleted gas well sequestration, enhanced coal-bed methane, aquifer sequestration, and ocean sequestration. The divided regions are interlinked through transportations of CO 2 and various kinds of energies. The model is an intertemporal optimization type; the objective function is the total cost of energy systems plus CO 2 sequestration between 2000 and 2050. Energy supply systems and CO 2 capture and sequestration technologies are represented in the bottom-up fashion in order to evaluate technological strategies of CO 2 emission mitigation technologies. CO 2 sequestration potentials of the 77 divided regions were estimated based on several geographical information systems (GIS) data. The model analysis results show that CO 2 sequestration accounts for a large part of the total CO 2 emission reduction; the amounts of the cumulative world CO 2 sequestration between 2000 and 2050 are about 45 GtC and 65 GtC with and without emission trading, respectively, and that the cost effective strategies differ by region. In the emission trading case, all the four types of underground CO 2 sequestration technologies are utilized for US; the sequestration into ocean and aquifer are utilized for Japan. CO 2 sequestration technologies would decrease the world marginal cost of CO 2 reduction in 2050 by about 59

Estimating option values of solar radiation management assuming that climate sensitivity is uncertain

/tC.

Estimates of GHG emission reduction potential by country, sector, and cost

Significance Stratospheric sulfur injection is an unprecedented manipulation of climate systems to rapidly decrease the global mean temperature and could entail environmental risk as well as confront ethical and governance challenges. Nonetheless, most studies have only evaluated impacts of solar radiation management (SRM) on the premise of its deployment. This paper presents one possible methodology for estimating option values of SRM assuming a fairly moderate scenario on SRM’s use compared with preceding literature, which would be helpful to examine realistic values of SRM for the society where social acceptability of SRM’s actual deployment is not high. Our results emphasize the near- to mid-term role of retaining SRM as a later risk-hedging option in the face of the uncertainty about climate sensitivity. Although solar radiation management (SRM) might play a role as an emergency geoengineering measure, its potential risks remain uncertain, and hence there are ethical and governance issues in the face of SRM’s actual deployment. By using an integrated assessment model, we first present one possible methodology for evaluating the value arising from retaining an SRM option given the uncertainty of climate sensitivity, and also examine sensitivities of the option value to SRM’s side effects (damages). Reflecting the governance challenges on immediate SRM deployment, we assume scenarios in which SRM could only be deployed with a limited degree of cooling (0.5 °C) only after 2050, when climate sensitivity uncertainty is assumed to be resolved and only when the sensitivity is found to be high (T2x = 4 °C). We conduct a cost-effectiveness analysis with constraining temperature rise as the objective. The SRM option value is originated from its rapid cooling capability that would alleviate the mitigation requirement under climate sensitivity uncertainty and thereby reduce mitigation costs. According to our estimates, the option value during 1990–2049 for a +2.4 °C target (the lowest temperature target level for which there were feasible solutions in this model study) relative to preindustrial levels were in the range between

Energy efficiency opportunities in the residential sector and their feasibility

2.5 and

Impact assessment of the increase in fossil fuel prices on the global energy system, with and without CO2 concentration stabilization

5.9 trillion, taking into account the maximum level of side effects shown in the existing literature. The result indicates that lower limits of the option values for temperature targets below +2.4 °C would be greater than

Analysis of Japan's energy and environment strategy after the Fukushima nuclear plant accident

2.5 trillion.