Mid-century emission pathways in Japan associated with the global 2 \xb0C goal: national and global models\u2019 assessments based on carbon budgets

Ken Oshiro,Pedro Rochedo,Jacques Després,Keii Gi,Christoph Bertram,Zoi Vrontisi,Shinichiro Fujimori,Mark Roelfsema,Toshihiko Masui,Heleen L Van Soest

doi:10.1007/s10584-019-02490-x

Abstract

This study assesses Japan’s mid-century low-emission pathways using both national and global integrated assessment models in the common mitigation scenario framework, based on the carbon budgets corresponding to the global 2 °C goal. We examine high and low budgets, equal to global cumulative 1600 and 1000 Gt-CO2 (2011–2100) for global models, and 36 and 31 Gt-CO2 (2011–2050) in Japan for national models, based on the cost-effectiveness allocation performed by the global models. The impacts of near-term policy assumption, including the implementation and enhancement of the 2030 target of the nationally determined contribution (NDC), are also considered. Our estimates show that the low budget scenarios require a 75% reduction of CO2 emissions by 2050 below the 2010 level, which is nearly the same as Japan’s governmental 2050 goal of reducing greenhouse gas emissions by 80%. With regard to near-term actions, Japan’s 2030 target included in the NDC is on track to meet the high budget scenario, whereas it is falling short for the low budget scenario, which would require emission reductions immediately after 2020. Whereas models differ in the type of energy source on which they foresee Japan basing its decarbonization process (e.g., nuclear- or variable renewable energy-dependent), the large-scale deployment of low-carbon energy (nuclear, renewable, and carbon capture and storage) is shared across most models in both the high and low budget scenarios. By 2050, low-carbon energy represents 44–54% of primary energy and 86–97% of electricity supply in the high and low budget scenarios, respectively.

Highlights

The Paris Agreement sets a goal to limit the average global temperature increase to well below 2 °C and to pursue efforts to limit the rise to 1.5 °C above pre-industrial levels
Cumulative emissions in the NDC1000 scenario were found to exceed the carbon budget in some models; this scenario is characterized by a deeper emission reduction in the second half of this century, and even the net removal of CO2 between 2051 and 2100
If near-term emissions follow the level of the nationally determined contribution (NDC), the net removal of CO2 would be required in the second-half of the century in the global 1000 Gt-CO2 scenario, which is equivalent to about 4.1 Gt-CO2, because cumulative emissions in the first half of the century exceed the national budget by 2100

Summary

Introduction

The Paris Agreement sets a goal to limit the average global temperature increase to well below 2 °C and to pursue efforts to limit the rise to 1.5 °C above pre-industrial levels. This article is part of a Special Issue on 'National Low-Carbon Development Pathways' edited by Roberto Schaeffer, Valentina Bosetti, Elmar Kriegler, Keywan Riahi, Detlef van Vuuren, and John Weyant. (IAMs), the collection of greenhouse gas (GHG) emissions implied by the nationally determined contributions (NDCs) is not on track with the optimal pathways toward the 2 °C goal (Rogelj et al 2016; van Soest et al 2017b; Vandyck et al 2016). Since the Paris Agreement parties are encouraged to formulate long-term low-emission development strategies, some parties have already submitted their mid-century strategies, including the emission reduction target by 2050. Some national and regional IAMs have been utilized to assess the NDCs and national mid-century pathways (Iyer et al 2017; Pye et al 2017)

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