Impact of China's digital economy on carbon emissions from the perspective of scale and efficiency

China's digital industry (DI) is vital in curbing carbon intensity. We constructed the mechanism of the DI on carbon intensity through energy structure and efficiency. We divided the development level of the DI into two perspectives: scale and efficiency. Based on industrial and regional differences, we empirically tested the influence of China's DI on carbon intensity through energy structure and efficiency. Our findings revealed that the role of the DI's scale surpassed its efficiency in curbing carbon intensity in China. Further, the DI's scale and efficiency significantly inhibited carbon intensity by improving energy efficiency; however, their inhibitory effect through optimising energy structure was limited. Moreover, the inhibitory effect of the DI on carbon intensity varied among industries and regions. Finally, we proposed measures to reduce carbon intensity when developing the DI.