— This study aims to analyze the causal factors affecting the efficiency of future environmental law enforcement in Thailand in order to achieve sustainability. The secondary data was collected from 2000 to 2019 with an application of the Path-Autoregressive Integrated Moving Average with exogenous variables model (Path-ARIMA-Vi model). The model was developed to forecast CO2 emission over the next 10 years (2020-2029). As of this study, the results show that the implementation of Thailand's Sustainable Development policy under environmental law leads to higher CO2 emission than the given carrying capacity. This increase was found with a growth rate of 41.1% (2029/2020) climbing up to 89.43. Mt CO2 Eq. (2020- 2029), which is higher than its stipulated carrying capacity of maximal 70.5 Mt CO2 Eq. (2020- 2029). Therefore, this study suggests provides a new scenario policy as part of national management strategy formulation while attaining sustainability under environmental law. The given policy is believed to result in the reduction of CO2 emission (2020-2029) to 64.44 Mt CO2 Eq. (2020-2029), which is at a lower rate than the given carrying capacity. With the same effect, it implies that the developed model in this study is highly effective for any decision-makings in a national management. Besides, it helps formulate better sustainable development policy under environmental law in order to achieve sustainability in the future