From air to rail: Carbon mitigation through modal shift in China’s intercity transport

Decarbonizing the transportation sector is a critical component of global climate change mitigation strategies. Achieving net-zero emissions in aviation remains particularly challenging due to the sector’s heavy reliance on carbon-intensive liquid fuels, as well as the substantial climate forcing from non-CO₂ effects such as contrails. In China, the rapid expansion of high-speed rail (HSR) provides a promising alternative to short- and medium-haul flights and has the potential to directly reduce aviation demand. However, the magnitude of its contribution to emission mitigation remains uncertain. In this study, we employ a difference-in-differences approach to quantify the causal impact of HSR introduction on domestic civil aviation in China. We estimate CO₂ emissions from both aviation and HSR, and further assess the additional substitution and mitigation potential of HSR under a set of future scenarios. Our results show that, between 2008 and 2019, the introduction of HSR led to a 24% reduction in aviation-related CO₂ emissions among city pairs connected by HSR. In 2019, CO₂ emissions from civil aviation and HSR were estimated at 87.0 and 17.9 Mt, respectively. Given the existing aviation and HSR networks in 2019, HSR operations could reduce aviation CO₂ emissions by approximately 9.1 Mt (10%). Under enhanced substitution conditions—assuming passengers are willing to extend travel time by up to two hours when switching to HSR, combined with power system decarbonization and full-speed HSR operation—the net mitigation potential increases to 50.6 Mt (48%) for the combined civil aviation and HSR transport system. Our findings demonstrate that HSR expansion can deliver substantial climate benefits by decarbonizing the civil aviation sector. With rising environmental awareness, continued electricity decarbonization, and accelerated HSR development, significantly larger emission reductions can be achieved through intermodal substitution.