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Abstract The roles of Arctic aerosols as ice-nucleating particles remain poorly understood, even though their effects on cloud microphysics are crucial for assessing the climate sensitivity of Arctic mixed-phase clouds and predicting their response to Arctic warming. Here we present a full-year record of ice-nucleating particle concentrations over Svalbard, where surface warming has been anomalously faster than the Arctic average. While the variation of ice-nucleating particles active at around −30 °C was relatively small, those active at higher temperatures (i.e., highly active ice-nucleating particles) tended to increase exponentially with rising surface air temperatures when the surface air temperatures rose above 0 °C and snow/ice-free barren and vegetated areas appeared in Svalbard. The aerosol population relevant to their increase was largely characterized by dust and biological organic materials that likely originated from local/regional terrestrial sources. Our results suggest that highly active ice-nucleating particles could be actively released from Arctic natural sources in response to surface warming.

Abstract Observed trends in tropospheric ozone, an important air pollutant and short‐lived climate forcer (SLCF), are estimated using available surface and ozonesonde profile data for 1993–2019, using a coherent methodology, and compared to modeled trends (1995–2015) from the Arctic Monitoring Assessment Program SLCF 2021 assessment. Increases in observed surface ozone at Arctic coastal sites, notably during winter, and concurrent decreasing trends in surface carbon monoxide, are generally captured by multi‐model median trends. Wintertime increases are also estimated in the free troposphere at most Arctic sites, with decreases during spring months. Winter trends tend to be overestimated by the multi‐model medians. Springtime surface ozone increases in northern coastal Alaska are not simulated while negative springtime trends in northern Scandinavia are not always reproduced. Possible reasons for observed changes and model performance are discussed including decreasing precursor emissions, changing ozone dry deposition, and variability in large‐scale meteorology.

Reduction in key air pollutants, especially particulate carbon, can help mitigate Arctic warming with associated benefits for global climate and human health, according to Earth system model simulations under future emissions scenarios.

Improved air quality is projected to weaken Atlantic Meridional Overturning Circulation but the effects can be offset by methane reductions, according to air quality control simulations based on the Shared Socio-economic Pathways.

Stratospheric meteorite dust particles can be entrained into the upper troposphere by tropopause folding, where the particles may affect cloud formation, according to electron microscopy of extraplanetary materials found within tropospheric sulfate aerosol particles

Abstract Changes in the hydrological cycle in the northern hemisphere (NH) have a significant socioeconomic impact. Thus, quantifying past changes and projecting future changes in this cycle are important. We analyzed the positive and negative multidecadal trends in the NH mean precipitation since the 1950s that were accurately reproduced by a state‐of‐the‐art Earth system model. Results showed that changes in the interhemispheric heat transport play a major role in the NH atmospheric heat budget, accounting for 59% of the negative‐to‐positive trend change in NH precipitation through a north–south shift in the tropical precipitation zone, and were strongly linked to Hadley circulation anomaly. The remaining 41% corresponded to changes in atmospheric cooling with small interhemispheric differences, which were primarily related to clear‐sky longwave radiation. These findings quantitatively agreed with the results from a multimodel analysis.

Abstract The observed sea level (SL) around the Japanese coast shows a peculiar multidecadal variation with the peak in the 1950s followed by the gradual fall until the 1970s and the rebound continuing to the present, making the recent SL rise less remarkable in the historical record. The multidecadal SL variability of an ensemble mean of the Coupled Model Intercomparison Project phase 6 historical simulations using the Meteorological Research Institute Earth System Model version 2.0 (MRI‐ESM2.0) compares well with the observation and is greater than the piControl one, implying the observed variability could be a forced one. The MRI‐ESM2.0 simulations for the Detection and Attribution Model Intercomparison Project suggest the increase in anthropogenic aerosols and greenhouse gases caused the fall and rise of the SL, respectively. Additional sensitivity runs indicate the surface heat loss in the North Pacific due to anthropogenic aerosols plays a dominant role in the SL fall.

This work presents an analysis of the effect of climate change on surface ozone discussing the related penalties and benefits around the globe from the global modelling perspective based on simulations with five CMIP6 (Coupled Model Intercomparison Project Phase 6) Earth System Models. As part of AerChemMIP (Aerosol Chemistry Model Intercomparison Project) all models conducted simulation experiments considering future climate (ssp370SST) and present-day climate (ssp370pdSST) under the same future emissions trajectory (SSP3-7.0). A multi-model global average climate change benefit on surface ozone of −0.96 ± 0.07 ppbv °C ^−1 is calculated which is mainly linked to the dominating role of enhanced ozone destruction with higher water vapour abundances under a warmer climate. Over regions remote from pollution sources, there is a robust decline in mean surface ozone concentration on an annual basis as well as for boreal winter and summer varying spatially from −0.2 to −2 ppbv °C ^−1 , with strongest decline over tropical oceanic regions. The implication is that over regions remote from pollution sources (except over the Arctic) there is a consistent climate change benefit for baseline ozone due to global warming. However, ozone increases over regions close to anthropogenic pollution sources or close to enhanced natural biogenic volatile organic compounds emission sources with a rate ranging regionally from 0.2 to 2 ppbv C ^−1 , implying a regional surface ozone penalty due to global warming. Overall, the future climate change enhances the efficiency of precursor emissions to generate surface ozone in polluted regions and thus the magnitude of this effect depends on the regional emission changes considered in this study within the SSP3_7.0 scenario. The comparison of the climate change impact effect on surface ozone versus the combined effect of climate and emission changes indicates the dominant role of precursor emission changes in projecting surface ozone concentrations under future climate change scenarios.