The importance and urgency of improving energy and carbon emissions efficiency in mitigating climate change and achieving carbon neutrality have become an increasingly relentless focus in recent years. Assessing the performance of energy saving and carbon emissions reduction is a significant necessity to achieve sustainable economic development. Therefore, from the perspective of production economics, this paper presents a review of the definition, models, and input-output variables for measuring total-factor energy efficiency and total-factor carbon emissions efficiency. Relevant literature in this field, published between 2006 and 2021, has been systematically analyzed using CiteSpace software, which includes a quantitative and visual review of a large body of published literature. This review found that the current definitions of total-factor energy efficiency and total-factor carbon emissions efficiency are confusing and misleading. Furthermore, future research on energy saving and carbon emissions reduction should incorporate subject areas such as economics, energy, and ecology.

Nowadays, sustainability has become an important and widely accepted concept. Energy conservation and emission reduction are closely related to sustainable economic development. Therefore, a 3E efficiency approach, based on the “Energy–Environmental–Economic” (3E) system, can assess the coordination relationships among these three factors from the perspective of energy conservation and emission reduction. The digital economy is a new driving force for economic growth, but few studies have dealt with the question on whether it affects 3E efficiency. The purpose of this paper is to examine the relationship between the digital economy and 3E efficiency in EU countries. The empirical results indicate that: (1) overall 3E efficiency of EU countries showed an upward trend from 2011 to 2019; (2) in terms of the relationship between the digital economy and 3E efficiency, the digital economy has direct and indirect (through economic growth) impacts on 3E efficiency; when GDP per capita exceeds EUR 15,580, the influence coefficient of the digital economy on 3E efficiency changes from negative to positive. This suggests that EU countries with different levels of economic development should adopt different strategies to ensure the simultaneous development of their digital economy and 3E efficiency.

Factor allocation has an important impact on production efficiency, and this study discusses factor misallocation and proposes an optimized method that could improve efficiency and reduce factor inputs. Under a multi-industry competitive equilibrium model, by introducing distortion tax that represents frictions on factor inputs (capital, labor, energy, and other intermediate consumption), we define factor price distortion indexes to measure factor misallocation and set the standardized comprehensive distortion index at the optimal value of one to obtain optimized allocation of each factor. Using actual and optimized inputs, we compute input-oriented efficiencies separately by employing a slack-based measurement data envelopment analysis (SBM-DEA). The superiority of the new allocation method is tested by comparing changes in efficiency and input redundancy before and after optimization. An empirical test based on China’s manufacturing sector during 1999–2016 shows that, under the optimized reallocation, on average, efficiency is improved by 43.40%, capital, labor, energy, and other intermediate consumption are reduced by 18.06%, 16.34%, 30.91%, and 31.24%, respectively, and the total carbon emission is reduced by 55.22% from 2000 to 2016. Our results imply that factor misallocation causes losses in efficiency and excessive input of factors, and factor allocation needs to be further optimized for sustainable development.