Does the Opening of Ports and Trading Affect Long- term Green Economic Efficiency?Evidence from China’s Yangtze River Delta

Taking the Yangtze River Delta of China as a case study, the SBM model GML index is used to measure urban green total factor productivity (GTFP), green technical efficiency (EC) and green technological progress (TC) respectively, and the multi-period spatial DID method is applied to empirically demonstrate the long-term heterogeneous effects of the late Qing Dynasty's open port and trade policy on urban green economic efficiency. The study concludes that (1) the late Qing Dynasty's policy of opening ports for trade objectively increased the city's long-term green total factor productivity (GTFP) and green technical efficiency (EC), but had an insignificant effect on green technological progress (TC). (2) The Treaty of Shimonoseki was a watershed in the long-term impact of the port-opening and trading policy on green economic efficiency, with the port-opening and trading policy implemented before 1895 boosting urban GTFP and EC, and the port-opening and trading policy implemented after 1895 having a negative impact on urban GTFP, EC and TC. (3) Long-term GTFP, EC and TC were negatively affected by the opening of ports and trading policies in cities where the governors were based, while opening of ports and trading policies in cities where the governors were not based had a positive effect on long-term GTFP, EC and TC. (4) Western powers following the civil law tradition had a more prominent long-term impact on the green economic efficiency of economically invaded cities than did common law countries. This paper appropriately verifies the long-term impact of open history on a city's green economic efficiency, which is instructive for better understanding, formulating and improving foreign opening policies in the new era.