This study employs a difference-in-difference (DID) regression to estimate the impact of high-speed rail (HSR) on city-level household carbon dioxide emissions across various consumption categories. The DID analysis is based on a sample of 179 Chinese cities during 2010-2018, and reveals a positive association between HSR and household carbon dioxide emissions. The findings suggest that cities with HSR emit more carbon dioxide due to increased daily consumption, and this effect grows over time. The mechanism analysis shows that the development of HSR stimulates household income growth, leading to increased consumption-based carbon dioxide in cities with HSR. Despite being considered a green transportation mode with a low carbon footprint, this research highlights potential environmental burdens associated with HSR, emphasizing the need for sustainable HSR development and environmental management policies.