Current National Determined Contributions require strengthening to achieve the 2-degree target set in the Paris Agreement. Here, we contrast two mitigation effort strengthening ideas: the "burden-sharing" principle, which requires each region to meet the mitigation goal through domestic mitigation with no international cooperation, and the cooperation focused "cost effective conditional-enhancing" principle, which combines domestic mitigation with carbon trading and low-carbon investment transfer. By applying a burden-sharing model covering several equity principles, we analyze the 2030 mitigation burden for each region, then the energy system model generates the results for the carbon trade and the investment transfer for the conditional-enhancing plan, and an air pollution cobenefit model is used to analyze the cobenefit on air quality and public health. Here, we show that the conditional-enhancing plan leads to an international carbon trading volume of 339.2 billion USD per year and reduces the marginal mitigation cost of the quota-purchase regions by 25%-32%. Furthermore, the international cooperation incentivizes a faster and deeper decarbonization in developing and emerging regions, raising the air pollution health cobenefits by 18% to 731,000 avoided premature deaths annually compared to the "burden-sharing" principle, amounting to a reduction in the life value loss of 131 billion dollars per year.
Keywords: 2-degree target; CO2 mitigation; NDCs; cobenefits; international cooperation.