ALBERT

Description: Radiative forcing by aerosol-cloud interaction (ACI) remains the largest uncertainty in climate projection based on the IPCC AR6 report in 2021. Many Earth system models tend to overestimate aerosol effective radiative forcing (ERF〈sub〉aer〈/sub〉) mainly because of the overly strong ACI forcing, including Department of Energy’s Energy Exascale Earth System Model (E3SM). In the effort to developing E3SM v3, we incorporated a new cloud microphysics scheme - the Predicted Particles Properties (P3) and the improved the deep convective wet removal treatments, aiming at providing better simulations of clouds, radiation, and ACI. We find that comparing with the original Morrison-Gettelman (MG2) scheme, the P3 improves shortwave cloud radiative forcing by over 1 W m〈sup〉-2〈/sup〉 and reduces ERF〈sub〉aer〈/sub〉 by 0.17 W m〈sup〉-2〈/sup〉 in global mean. By improving aerosol wet removal treatments for deep convection (e.g., cloud-borne aerosol detrainment, aerosol secondary activation, and cloud-borne aerosol removal), we effectively decrease the overestimation of aerosol burden and lifetime, and reduce the positive biases in aerosol optical depth and aerosol mass concentration. The resultant direct and indirect forcing components of ERF〈sub〉aer〈/sub〉 are significantly decreased. With some further turning in the minimal cloud droplet number concentrations (Nc), the autoconversion Nc exponent, and the subgrid factor for ice nucleation in cirrus clouds, we can achieve an aerosol forcing of about -0.9 W m〈sup〉-2〈/sup〉 which is well within the reference range by IPCC AR6 report. Such effort addresses the outstanding issue of E3SM - unreasonably strong ERF〈sub〉aer〈/sub〉, which would help reproduce the global temperature trend since the industrial revolution.

Description: Chinese cities are core in the national carbon mitigation and largely affect global decarbonisation initiatives, yet disparities between cities challenge country-wide progress. Low-carbon transition should preferably lead to a convergence of both equity and mitigation targets among cities. Inter-city supply chains that link the production and consumption of cities are a factor in shaping inequality and mitigation but less considered aggregately. Here, we modelled supply chains of 309 Chinese cities for 2012 to quantify carbon footprint inequality, as well as explored a leverage opportunity to achieve an inclusive low-carbon transition. We revealed significant carbon inequalities: the 10 richest cities in China have per capita carbon footprints comparable to the US level, while half of the Chinese cities sit below the global average. Inter-city supply chains in China, which are associated with 80% of carbon emissions, imply substantial carbon leakage risks and also contribute to socioeconomic disparities. However, the significant carbon inequality implies a leveraging opportunity that substantial mitigation can be achieved by 32 super-emitting cities. If the super-emitting cities adopt their differentiated mitigation pathway based on affluence, industrial structure, and role of supply chains, up to 1.4 Gt carbon quota can be created, raising 30% of the projected carbon quota to carbon peak. The additional carbon quota allows the average living standard of the other 60% of Chinese people to reach an upper-middle-income level, highlighting collaborative mechanism at the city level has a great potential to lead to a convergence of both equity and mitigation targets.