Efforts-sharing to achieve the Paris goals: Ratcheting-up of NDCs and taking full advantage of international carbon market.

• Most countries should strengthen NDC targets for reaching the long-term climate goals. • The reduction efforts of major countries for meeting the climate goals are determined. • Many developed regions should halve their NDC emissions in 2030 for reaching 1.5 °C. • Global GDP losses for meeting 2 °C and 1.5 °C decrease by 69% and 50% through permits trading. Aggregated mitigation efforts represented by current Nationally Determined Contributions (NDCs) fall far short of meeting the 2 °C and 1.5 °C Paris goals, and Parties should enhance their mitigation targets through a ratcheting-up mechanism to close the large gap. The paper first assesses the stringency of major emitters' NDCs based on a comparison with the seven equity allocations. Then, it proposes a novel ratcheting-up scheme which distributes the mitigation gap between aggregated NDCs and the Paris goals based on key equity criteria and calculates the additional emission reduction rates for countries with insufficient ambitions. To fully consider different ambition levels of NDCs and also avoid overambitious outcomes, lower and upper limits are set for individual country's reduction rate, thus improving the equity and feasibility of the scheme. The results indicate that most countries should strengthen current efforts. By 2030, countries with insufficient NDCs need to reduce their aggregated emissions by 23% and 36% respectively to achieve the 2 °C and 1.5 °C goals. Most developed countries should undertake reduction rates which are above the global average level. Under the 1.5 °C pathway, many developed countries need to reduce their NDC emissions by about 50% in 2030. The mitigation costs of achieving the Paris goals as well as the benefits of international emissions trading have been evaluated. The results show that global GDP losses in 2030 for achieving 2 °C and 1.5 °C could decrease by 69% and 50% respectively through permits trading, and regional GDP losses would also be reduced, highlighting the importance of an effective global carbon market for meeting the Paris goals. [ABSTRACT FROM AUTHOR]