Synergy evaluation of China's economy-energy low-carbon transition and its improvement strategy for structure optimization

Low-carbon economic development and energy transition are interactively linked. The synergetic development of the two subsystems is important to achieve the "double carbon" goal of sustainable development. First, this study proposes a model to measure the current synergy level of China's economy-energy low-carbon transition. Second, an optimization model is developed to improve industry and energy synergy levels through structure optimization. The synergy degree (SD) level of China's economy-energy low-carbon transition increased from 0 to 0.98 between 2005 and 2017. Furthermore, 69.2% of the periods are in a state of asynergy (SD < 0.6). By implementing the industry and energy structure optimization (OPT) scenario, the synergy level by 2035 can be 27.8% higher than the business-as-usual (BAU) scenario. Moreover, light synergy (0.6 <= SD < 0.8) could be achieved by 2025, and high-quality synergy (0.9 <= SD <= 1) by 2033 in the OPT scenario. Conversely, the synergy level can only achieve light synergy until 2035 in the BAU scenario. Compared to energy structure optimization, the low carbonization of the economic structure plays a more significant role in improving the synergy level of the transaction. These findings can provide support for China's policy-making regarding economic and energy transition.