To mitigate climate warming, many countries have committed to achieve carbon neutrality in the mid-21^st century. Here, we assess the global impacts of changing greenhouse gases (GHGs), aerosols, and tropospheric ozone (O₃) following a carbon neutrality pathway on climate and extreme weather events individually using the Community Earth System Model version 1 (CESM1). The results suggest that the future aerosol reductions significantly contribute to climate warming and increase the frequency and intensity of extreme weathers toward carbon neutrality and aerosol impacts far outweigh those of GHGs and tropospheric O₃. It reverses the knowledge that the changing GHGs dominate the future climate changes as predicted in the middle of the road pathway. Therefore, substantial reductions in GHGs and tropospheric O₃ are necessary to reach the 1.5 °C warming target and mitigate the harmful effects of concomitant aerosol reductions on climate and extreme weather events under carbon neutrality in the future.

As a major alkaline gas in the atmosphere, NH₃ significantly impacts atmospheric chemistry, ecological environment, and biodiversity. Gridded NH₃ emission inventories can significantly affect the accuracy of model concentrations and play a crucial role in the refinement of mitigation strategies. However, several uncertainties are still associated with existing NH₃ emission inventories in China. Therefore, in this study, we focused on improving fertilizer-application-related NH₃ emission inventories. We comprehensively evaluated the dates and times of fertilizer application to the major crops that are cultivated in China, improved the spatial allocation methods for NH₃ emissions from croplands with different rice types, and established a gridded NH₃ emission inventory for mainland China with a resolution of 5 min × 5 min in 2016. The results showed that the atmospheric NH₃ emissions in mainland China amounted to 12.11 Tg, with livestock waste (44.8 %) and fertilizer application (38.6 %) being the two main NH₃ emission sources in China. Obvious spatial variability in NH₃ emissions was also identified, and high emissions were predominantly concentrated in North China. Further, NH₃ emissions tended to be high in summer and low in winter, and the ratio for the July–January period was 3.08. Furthermore, maize and rice fertilization in summer was primarily responsible for the increase in NH₃ emissions in China, and the evaluation of the spatial and temporal accuracy of the NH₃ emission inventory established in this study using the WRF-Chem and ground-station- and satellite-based observations showed that it was more accurate than other inventories.

A large population in China has been exposed to both severe ozone (O ₃ ) pollution and extreme heat under global warming. Here, the spatiotemporal characteristics of coupled extremes in surface O ₃ and heat (OPCs) over China are investigated using surface observations, a process-based chemical transport model (GEOS-Chem), and multi-model simulations from Phase 6 of the Coupled Model Intercomparison Project (CMIP6). North China Plain (NCP; 37–41 ^∘ N; 114–120 ^∘ E) is identified as a hot spot of OPCs, where more than half of the O ₃ pollution days are accompanied by high temperature extremes. OPCs over NCP exceeded 40 d during 2014–2019, exhibiting an increasing trend. Both O ₃ concentrations and temperatures are elevated during OPCs compared with O ₃ pollution days occurring individually (OPIs). Therefore, OPCs impose more severe health impacts to humans than OPIs, but the stronger health effects are mainly driven by the higher temperatures. GEOS-Chem simulations further reveal that enhanced chemical production resulting from hot and stable atmospheric conditions under anomalous weather patterns primarily contributes to the exacerbated O ₃ levels during OPCs. In the future, CMIP6 projections suggest increased occurrences of OPCs over NCP in the middle of this century, but by the end of this century, OPCs may decrease or increase depending on the pollutant emission scenarios. However, for all future scenarios, extreme high temperatures will play an increasingly important role in modulating O ₃ pollution in a warming climate.

The reduced human activities and associated decreases in aerosol emissions during the COVID‐19 pandemic are expected to affect climate. Assuming emission changes during lockdown, back‐to‐work and post‐lockdown stages of COVID‐19, climate model simulations show a surface warming over continental regions of the Northern Hemisphere. In January–March, there was an anomalous warming of 0.05–0.15 K in eastern China, and the surface temperature increase was 0.04–0.07 K in Europe, eastern United States, and South Asia in March–May. The longer the emission reductions undergo, the warmer the climate would become. The emission reductions explain the observed temperature increases of 10–40% over eastern China relative to 2019. A southward shift of the ITCZ is also seen in the simulations. This study provides an insight into the impact of COVID‐19 pandemic on global and regional climate and implications for immediate actions to mitigate fast global warming.

Ozone (O₃) is one of the most critical pollutants affecting air quality in China in recent years. In this study, different impacts of the El Niño–Southern Oscillation (ENSO) warm/cold phases on summertime tropospheric O₃ over China are examined based on model simulations, ground measurements, and reanalysis data. Summertime surface O₃ concentrations in China show a positive correlation with ENSO index during years 1990–2019, with the largest increases by 20% over southern China in El Niño (warm phase) relative to La Niña (cold phase) years. The ENSO modulation extends to the middle and even upper troposphere. Our analysis indicates that O₃ flux convergence associated with weakened southerlies is the primary reason for the increase in tropospheric O₃ over southern China. In addition, the O₃ increase during El Niño years is mainly from domestic emissions in China. This study highlights the potential significance of ENSO in modulating tropospheric O₃ concentrations in China, with great implications for O₃ pollution mitigation.

Record rainfall and severe flooding struck eastern China in the summer of 2020. The extreme summer rainfall occurred during the COVID-19 pandemic, which started in China in early 2020 and spread rapidly across the globe. By disrupting human activities, substantial reductions in anthropogenic emissions of greenhouse gases and aerosols might have affected regional precipitation in many ways. Here, we investigate such connections and show that the abrupt emissions reductions during the pandemic strengthened the summer atmospheric convection over eastern China, resulting in a positive sea level pressure anomaly over northwestern Pacific Ocean. The latter enhanced moisture convergence to eastern China and further intensified rainfall in that region. Modeling experiments show that the reduction in aerosols had a stronger impact on precipitation than the decrease of greenhouse gases did. We conclude that through abrupt emissions reductions, the COVID-19 pandemic contributed importantly to the 2020 extreme summer rainfall in eastern China.