The Arctic is notable as a region where the greatest rate of increase in precipitation associated with global warming is anticipated. The Arctic precipitation simulated by the Coupled Model Intercomparison Project phase 6 multimodels showed a strong increasing trend in the recent past since the 1980s as a result of the continued strengthening of greenhouse gas forcing. Meanwhile, the suppression by aerosol forcing, which dominated in earlier periods, has been leveled off. From an energetic perspective, the constraining factors of increased atmospheric radiative cooling and reduced heat transport from lower latitudes contributed equally to the recent increase in Arctic precipitation. Future Arctic precipitation will change in proportion to the temperature change, but the fractional contributions of the constraining factors will remain stable across various scenarios. The implications for the doubling of the Arctic amplification factor of precipitation changes relative to that of temperature changes are also discussed.

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, observed trends are compared to modeled trends (1995-2015) from the Arctic Monitoring Assessment Programme SLCF 2021 assessment. Statistically significant 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 (MMM) trends. Wintertime increases are also estimated in the free troposphere at most Arctic sites, but tend to be overestimated by the MMMs. 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 behavior are discussed, including decreasing precursor emissions, changing ozone sinks, and variability in large-scale meteorology.

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. An ensemble mean of the historical simulations conducted for the Coupled Model Intercomparison Project phase 6 (CMIP6) using the Meteorological Research Institute Earth System Model version 2.0 (MRI-ESM2.0) reproduces this variability well, implying that this was a forced one. The MRI-ESM2.0 simulations for the Detection and Attribution Model Intercomparison Project suggest that the increase in anthropogenic aerosols caused the SL fall from the 1950s to the 1970s and the increase in greenhouse gases caused the SL rise after that. Additional sensitivity runs indicate that the surface heat loss in the North Pacific due to anthropogenic aerosols plays a dominant role in the SL fall.

The representations of clouds in climate model MRI-ESM2 (Yukimoto et al. 2019, JMSJ) used in CMIP6 simulations are significantly improved from the previous version MRI-CGCM3 used in CMIP5 simulations. The score of the spatial pattern of 2m temperature for MRI-ESM2 is better than any of the 47 CMIP6 models. The score for radiative fluxes at the top of the atmosphere for MRI-ESM2 is ranked in the top seven models among these CMIP6 models. We will introduce comprehensively various modifications related to clouds, which contribute to the dramatically improved cloud representation, and their main impacts (Kawai et al. 2019, GMD). The modifications cover various schemes and processes including the cloud scheme, turbulence scheme, cloud microphysics processes, the interaction between cloud and convection schemes, resolution issues, cloud radiation processes, aerosol properties, and numerics. In addition, we would like to mention what data we used during the model development, how we evaluated our model, how useful the intercomparison studies were, and what data we need for further model development.

We quantify the impacts of halogenated ozone-depleting substances (ODSs), methane, N2O, CO2, and short-lived ozone precursors on total and partial ozone column changes between 1850 and 2014 using CMIP6 Aerosol and Chemistry Model Intercomparison Project (AerChemMIP) simulations. We find that whilst substantial ODS-induced ozone loss dominates the stratospheric ozone changes since the 1970s, the increases in short-lived ozone precursors and methane lead to increases in tropospheric ozone since the 1950s that make increasingly important contributions to total column ozone (TCO) changes. Our results show that methane impacts stratospheric ozone changes through its reaction with atomic chlorine leading to ozone increases, but this impact will decrease with declining ODSs. The N2O increases mainly impact ozone through NOx-induced ozone destruction in the stratosphere, having an overall small negative impact on TCO. CO2 increases lead to increased global stratospheric ozone due to stratospheric cooling. However, importantly CO2 increases cause TCO to decrease in the tropics. Large interannual variability obscures the responses of stratospheric ozone to N2O and CO2 changes. Substantial inter-model differences originate in the models’ representations of ODS-induced ozone depletion. We find that, although the tropospheric ozone trend is driven by the increase in its precursors, the stratospheric changes significantly impact the upper tropospheric ozone trend through modified stratospheric circulation and stratospheric ozone depletion. The speed-up of stratospheric overturning (i.e. decreasing age of air) is driven mainly by ODS and CO2; increases. Changes in methane and ozone precursors also modulate the cross-tropopause ozone flux.