The analyses on the economic costs for achieving the nationally determined contributions and the expected global emission pathways

Abstract

The Paris Agreement for a post-2020 international framework for tackling climate change was adopted in December 2015. The agreement requires that each country prepares and communicates nationally determined contributions (NDCs) every 5 years, including greenhouse gas (GHG) emission reduction targets. Most countries submitted NDCs before the Paris Agreement. According to our analyses using a global energy and GHG emission reduction assessment model, the emission reduction costs of the NDCs vary widely among countries; and those differences will induce carbon leakage, thus the expected global emission reduction is smaller than that predicted by simply aggregating the emission reductions of all the countries. Moreover, the emissions are larger than those required for the pathways leading to a high probability of temperature stabilization at below 2 °C above pre-industrial levels. To fill the gap, a rigorous review process employing robust indicators measuring emission reduction efforts is crucial. However, the development and deployment of innovative technologies with cheaper costs is even more significant.

Appendix: Overview of the global energy and GHG emission reduction assessment model DNE21+

The DNE21+ model (Akimoto et al. 2010; 2014) is an intertemporal linear programming model for the assessment of global energy systems and global warming mitigation in which the worldwide costs are to be minimized. The model represents regional differences, and assesses detailed energy-related CO₂ emission reduction technologies up to 2050. When any emission restriction (e.g., an upper limit of emissions, emission reduction targets, targets of energy or emission intensity improvements, or carbon taxes) is applied, the model specifies the energy systems whose costs are minimized, meeting all the assumed requirements, including assumed production for industries such as iron and steel, cement, and paper and pulp, transportation by automobile, bus, and truck, and other energy demands. The energy supply sectors are hard-linked with the energy end-use sectors, including energy exporting/importing, and the lifetimes of facilities are taken into account so that assessments are made with complete consistency kept over the energy systems. Salient features of the model include (1) analysis of regional differences between 54 world regions while maintaining common assumptions and interrelationships, (2) a detailed evaluation of global warming response measures that involves modeling of about 300 specific technologies that help suppress global warming, and (3) explicit facility replacement considerations over the entire time period. Based on the plausible ranges derived from the relevant literature, the model assumes energy efficiency improvements in several kinds of technologies and cost reductions of renewable energies, carbon dioxide capture and storage (CCS), amongst others.