The United States has achieved economic growth compatible with carbon reduction since 2007. This work is addressed to understand the eight effects, especially effects related to research & development (R&D) on the decoupling economic growth from carbon emission through a decomposition technique and a decoupling effort model. The results of sector analysis show that the changes of carbon emission in industry sector and transportation sector were dominant contributor and inhibitor to the drop of carbon emission, respectively. The decomposition results indicate that energy intensity was the leading contributor to the drop of carbon emission, followed by R&D intensity, sectoral carbon intensity, R&D efficiency; whereas economic scale was the primary inhibitor to the drop of carbon emission, followed by investment intensity, population size and sectoral energy structure. The results of decoupling efforts analysis uncover that energy intensity, R&D intensity, R&D efficiency and sectoral carbon intensity contributed to decoupling economic growth from carbon emission, whereas investment intensity, population size and sectoral energy structure did not contribute to the decoupling. Finally, some policy implications are proposed.

Introduction

In recent decades, global warming has received considerable attention and concerns, due to its negative impact on social and economic development. International community has been making great efforts to control climate change, from United Nations Framework Convention on Climate Change, Kyoto Protocol to The Paris Agreement. Carbon emission is one of main contributors to global warming. According to Global Carbon Project (GCP), total global carbon emission exceeded 30 billion tons, increased by1.6% in 2017. While in 2018, it is expected to increase by 2.7%, having possibility to hit a New High. Carbon emission from energy consumption accounts for nearly 80% of total global carbon emission. Therefore, controlling energy-related carbon emission will play a critical role in restraining global carbon emission and temperature rise. The United States announced to withdraw Kyoto Protocol in 2001. However, despite the government did not perform international responsibility of fighting against climate change together with international community, its energy-related carbon emission reached the peak of 6006 million tons in 2007, then progressively decreased, truly achieving decoupling. Hence, it is of great significance to figure out underlying reasons to decoupling energyrelated carbon emission from economic growth in the United States.