Yasuaki Hijioka

Will international emissions trading help achieve the objectives of the Paris Agreement

Under the Paris Agreement, parties set and implement their own emissions targets as nationally determined contributions (NDCs) to tackle climate change. International carbon emissions trading is expected to reduce global mitigation costs. Here, we show the benefit of emissions trading under both NDCs and a more ambitious reduction scenario consistent with the 2 °C goal. The results show that the global welfare loss, which was measured based on estimated household consumption change in 2030, decreased by 75% (from 0.47% to 0.16%), as a consequence of achieving NDCs through emissions trading. Furthermore, achieving the 2 °C targets without emissions trading led to a global welfare loss of 1.4%–3.4%, depending on the burden-sharing scheme used, whereas emissions trading reduced the loss to around 1.5% (from 1.4% to 1.7%). These results indicate that emissions trading is a valuable option for the international system, enabling NDCs and more ambitious targets to be achieved in a cost-effective manner.

Global‐scale analysis on future changes in flow regimes using Gini and Lorenz asymmetry coefficients

By introducing two scalar quantities, namely, the Gini and Lorenz asymmetry coefficients, we examined their characteristics and applicability to the global analysis of changes in river flow regimes under future climate change. First, by applying these coefficients to river discharge data, we showed that various types of flow-duration curves can be interpreted quantitatively in terms of the seasonal inequality in the discharge (i.e., the unevenness of the temporal distribution of river discharge). Their statistical characteristics, based on five theoretical distribution functions frequently used in hydrological analysis, were also shown. Next we used these coefficients to evaluate the seasonal inequality of major global rivers using the global hydrological model H08 for four 30 year time spans (1960–1989, 2010–2039, 2040–2069, and 2070–2099) under four climate-change scenarios. We used ensembles of hydrological simulation results with five general circulation models. From the analysis of the Gini coefficient, future changes in seasonal inequality show a contrasting geographical pattern: a decreasing trend at high northern latitudes and an increasing trend in most other areas. The Lorenz asymmetry coefficient shows large changes at high northern latitudes, attributable to major shifts in the flow regime accompanied by different snow-melting properties under different future climate scenarios. Although a flow-duration curve is a pictorial representation of river discharge suitable for one specific site, by depicting the geographical distribution of these two coefficients along river channels, different characteristics of flow-duration curves at different sites can be detected, even within the same river basin.

Potential Impacts of Global Climate Change

AIM/Impact model, an integrated assessment model of climate change impacts, has been developed in order to evaluate future climate change impacts and to support decision making on the global/Asia scale. AIM/Impact model consists of sub-models for evaluating impacts on major vulnerable sectors (water, agriculture, ecosystem, human health) and linkages among them. In this chapter, the general framework of AIM/Impact and examples of model outputs are introduced with a brief description of the sub-models.

Adaptation pathways of global wheat production: Importance of strategic adaptation to climate change

Agricultural adaptation is necessary to reduce the negative impacts of climate change on crop yields and to maintain food production. However, few studies have assessed the course of adaptation along with the progress of climate change in each of the current major food producing countries. Adaptation pathways, which describe the temporal sequences of adaptations, are helpful for illustrating the timing and intensity of the adaptation required. Here we present adaptation pathways in the current major wheat-producing countries, based on sequential introduction of the minimum adaptation measures necessary to maintain current wheat yields through the 21st century. We considered two adaptation options: (i) expanding irrigation infrastructure; and (ii) switching crop varieties and developing new heat-tolerant varieties. We find that the adaptation pathways differ markedly among the countries. The adaptation pathways are sensitive to both the climate model uncertainty and natural variability of the climate system, and the degree of sensitivity differs among countries. Finally, the negative impacts of climate change could be moderated by implementing adaptations steadily according to forecasts of the necessary future adaptations, as compared to missing the appropriate timing to implement adaptations.

Intercomparison of global river discharge simulations focusing on dam operation—multiple models analysis in two case-study river basins, Missouri–Mississippi and Green–Colorado

We performed a twofold intercomparison of river discharge regulated by dams under multiple meteorological forcings among multiple global hydrological models for a historical period by simulation. Paper II provides an intercomparison of river discharge simulated by five hydrological models under four meteorological forcings. This is the first global multimodel intercomparison study on dam-regulated river flow. Although the simulations were conducted globally, the Missouri-Mississippi and Green- Colorado Rivers were chosen as case-study sites in this study. The hydrological models incorporate generic schemes of dam operation, not specific to a certain dam. We examined river discharge on a longitudinal section of river channels to investigate the effects of dams on simulated discharge, especially at the seasonal time scale. We found that the magnitude of dam regulation differed considerably among the hydrological models. The difference was attributable not only to dam operation schemes but also to the magnitude of simulated river discharge flowing into dams. That is, although a similar algorithm of dam operation schemes was incorporated in different hydrological models, the magnitude of dam regulation substantially differed among the models. Intermodel discrepancies tended to decrease toward the lower reaches of these river basins, which means model dependence is less significant toward lower reaches. These case-study results imply that, intermodel comparisons of river discharge should be made at different locations along the rivers course to critically examine the performance of hydrological models because the performance can vary with the locations.

Potential of existing policies of the Tokyo Metropolitan Government for implementing adaptation to climate change

The impacts of climate change are apparent in various regions of the world. Even though climate change may have a positive effect, it is anticipated that there will be many severely negative effects on human and natural resources in the future. Therefore, in addition to the need for stronger promotion of mitigation policies, it is urgently necessary to study and implement adaptation policies over the longer term to prepare for the possible negative impact of climate change. To implement climate change adaptation measures rapidly in Japan, it would seem practical and effective to make good use of the various countermeasures already promoted by both the national and the local governments for many sectors such as disaster prevention, environmental management, food production, and protection of the nation’s health. These countermeasures are considered to have potential for effecting climate change adaptation. This study, focusing on adaptation to climate change negative impacts, investigates to what extent the existing policies of the Tokyo Metropolitan Government could contribute to climate change adaptation, based on a comprehensive examination of targeted fields and indicators for which adaptation policies could be pursued. The results showed many of the existing policies could be useful for adaptation to climate change in many sectors. Furthermore, less than half of these policies need to take future climate change into account in order to contribute to climate change adaptation. This study proposes three basic steps that consider future climate change and local governmental propositions for the rapid implementation of adaptation policies in Japan.

The Effect of Precipitation on the Transmission of Japanese Encephalitis (JE) Virus in Nature: A Complex Effect on Antibody-Positive Rate to JE Virus in Sentinel Pigs

Japanese encephalitis (JE) is one of the most important mosquito-borne viral diseases in Asia. Pigs are a natural host and the amplifier of JE virus. The sero-conversion rate to JE virus in sentinel pigs reflects the activity of JE virus in the region. We analyzed whether precipitation has any effect on the sero-conversion rate to JE virus in sentinel pigs. Linear regression analysis was performed to determine the correlations between the levels of precipitation and sero-conversion rates to JE virus, in the entire year and during summertime over the period of 32 years from 1969 to 2000. The levels of the annual and summertime precipitation demonstrated statistically significant positive correlations with sero-conversion rates for the whole of the country and for some regions in Japan. The levels of the summertime precipitation, on the other hand, demonstrated statistically significant inverse correlations with the sero-conversion rates in other regions. Further, the levels of precipitation during preceding 10-day periods from days 1–40 before blood collection showed inverse correlation with antibody-positive rates in some regions. The results indicate that the relationship between the annual and summertime precipitation, and the sero-conversion rate to JE virus is complex; both positive and inverse effects are demonstrated depending on the regions.

Economic consequences of global climate change and mitigation on future hydropower generation

Hydropower generation plays a key role in mitigating GHG emissions from the overall power supply. Although the maximum achievable hydropower generation (MAHG) will be affected by climate change, it is seldom incorporated in integrated assessment models. In this study, we first used the H08 global hydrological model to project MAHG under two physical climate change scenarios. Then, we used the Asia-Pacific Integrated Model/Computable General Equilibrium integrated assessment model to quantify the economic consequences of the presence or absence of mitigation policy on hydropower generation. This approach enabled us to quantify the physical impacts of climate change and the effect of mitigation policy—together and in isolation—on hydropower generation and the economy, both globally and regionally. Although there was little overall global change, we observed substantial differences among regions in the MAHG average change (from − 71% in Middle East to 14% in Former Soviet Union in RCP8.5). We found that the magnitude of changes in regional gross domestic product (GDP) was small negative (positive) in Brazil (Canada) by 2100, for the no mitigation policy scenario. These consequences were intensified with the implementation of mitigation policies that enhanced the price competitiveness of hydropower against fossil fuel-powered technologies. Overall, our results suggested that there would be no notable globally aggregated impacts on GDP by 2100 because the positive effects in some regions were canceled out by negative effects in other regions.

Consequences of implementing a reservoir operation algorithm in a global hydrological model under multiple meteorological forcing

ABSTRACT We investigated dam behaviours during high-flow events and their robustness against perturbations in meteorological conditions using the H08 global hydrological model. Differences in these behaviours were examined by comparing simulation runs, with and without dams and using multiple meteorological datasets, at a case-study site, Fort Peck Dam on the Missouri River, USA. The results demonstrated that dam-regulated river flow reduced temporal variability over large time periods and also dampened inter-forcing discrepancies in river discharge (smoothing effects). However, during wet years, differences in peak flow were accentuated downstream of the dam, resulting in divergence in simulated peak flow across the meteorological forcing (pulsing effect). The pulsing effect was detected at other major dams in global simulations. Depending upon the meteorological forcing, the dams act as a selective filter against high-flow events. Synergy between a generic dam scheme and differences in meteorological forcing data might introduce additional uncertainties in global hydrological simulations.

A review of quality of life (QOL) assessments and indicators: Towards a “QOL-Climate” assessment framework

Quality of life (QOL), although a complex and amorphous concept, is a term that warrants attention, especially in discussions on issues that touch on the impacts of climate change and variability. Based on the principles of RepOrting standards for Systematic Evidence Synthesis, we present a systematic review aimed at gaining insights into the conceptualization and methodological construct of previous studies regarding QOL and QOL-related indexes. We find that (i) QOL assessments vary in terms of conceptual foundations, dimensions, indicators, and units of analysis, (ii) social indicators are consistently used across assessments, (iii) most assessments consider indicators that pertain to the livability of the environment, and (iv) QOL can be based on objective indicators and/or subjective well-being, and on a composite index or unaggregated dimensions and indicators. However, we also find that QOL assessments remain poorly connected with climate-related issues, an important research gap. Our proposed “QOL-Climate” assessment framework, designed to capture the social-ecological impacts of climate change and variability, can potentially help fill this gap.