The quasi-biennial oscillation (QBO) is the main mode of variability in the tropical stratosphere, influencing the predictability of other regions in the atmosphere through its teleconnections to the stratospheric polar vortices and coupling to surface tropical and extratropical variability. However, climate and forecasting models consistently underestimate QBO amplitudes in the lower stratosphere, likely contributing to their failure to simulate these teleconnections. One underexplored contributor to model biases is missing representation of ozone-radiative feedbacks, which enhance temperature variability in the lower stratosphere, particularly at periods at and greater than the QBO (>28 months). While previous studies suggest that ozone-radiative feedbacks can impact QBO periods, amplitudes and the associated secondary circulation in the lower stratosphere, the reported impacts differ widely among models and are hard to interpret due to differences in methodology. To this end, here we propose a coordinated experimental protocol - held joint between the Atmospheric Processes and their Role in Climate (APARC) Quasi-Biennial Oscillation Initiative (QBOi) and Chemistry Climate Modeling Initiative (CCMI) activities - which is aimed at assessing the coupling between stratospheric ozone, temperature and the circulation. We use the proposed experiments to define the ozone feedback on the QBO in both present-day and idealized (abrupt quadrupling of carbon dioxide) climates. While primary focus is on the QBO, the proposed protocol also enables analysis of other aspects of ozone-radiative-dynamical coupling in the atmosphere, including impacts on the Brewer-Dobson Circulation and tropospheric eddy-driven jet responses to future climate change. Here we document the scientific rationale and design of the QUOCA Phase 1 experiments, summarize the data request, and give a brief overview of participating models. Preliminary results using the NASA Goddard Institute for Space Studies E2-2 climate model are used to illustrate sensitivities to certain methodological choices.

Ambitious climate and air quality mitigation cuts anthropogenic aerosol emissions, lowering fine particulate matter (PM 2.5 ) and mortality, but the magnitude, regional distribution, and uncertainty of these reductions remain insufficiently quantified. Using nine Earth System Models from the Regional Aerosol Model Intercomparison Project (RAMIP), we quantify the PM 2.5 mortality benefits of switching anthropogenic aerosols alone from a low mitigation (SSP3-7.0) to a high mitigation (SSP1-2.6) scenario. The switch averts 2.36 million (95% CI: 1.48–2.57 million) deaths/year globally, 38% of SSP3-7.0 PM 2.5 -attributable mortality. Benefits are largest in East Asia, South Asia, and Africa and smaller in North America and Europe. Global land annual mean PM 2.5 falls by 2%–17% across the RAMIP experiments, reaching 33–38% near Asian sources. Cuts in East Asia alone avert 48% of source region and 22% of global PM 2.5 mortality. Uncertainty is dominated by inter-model variability, followed by health response functions and natural climate variability. Overall, sustainability-pathway aerosol reductions can avert nearly 40% of projected PM2.5 deaths by 2050, with health benefits that are large but highly unevenly spatially distributed.

In response to continued greenhouse gas (GHG) increases, the Atlantic Meridional Overturning Circulation (AMOC) is expected to weaken through the 21st century. However, AMOC impacts associated with efforts to improve air quality are less well understood. Here, eight models from the Regional Aerosol Model Intercomparison Project are examined to quantify mid-21st century AMOC changes resulting from global and regional anthropogenic aerosol and precursor gas (AA) emissions reductions (industrial and biomass burning), by comparing strong air pollution control shared socioeconomic pathway (SSP1-2.6) to a baseline with weak air pollution control (SSP3-7.0). Global AA reductions and subsequent warming yield multi-model mean AMOC weakening of 6% ( -0.98 +/- 0.40 Sv; 1 Sv = 106 m3 s-1) by the last 12 years of the simulation (2039-2050). This is 1/3 of the magnitude of the corresponding weakening associated with the high GHG emissions scenario SSP3-7.0. Of the regional perturbations, combined North American and European AA reductions drive the largest AMOC weakening, followed by combined African and Middle Eastern reductions and then East Asian reductions, with South Asian reductions yielding non-significant weakening. Across these experiments, AMOC weakening is significantly correlated with the North Atlantic Ocean aerosol effective radiative forcing ( r=-0.95) and aerosol optical depth response ( r=1.0). AMOC weakening under AA reductions is associated with a thermally driven reduction in buoyancy in the subpolar North Atlantic, which is largely driven by surface shortwave radiation increases, consistent with the forcing from AA reductions. Africa + Middle East AA reductions also involve excitation of a negative North Atlantic Oscillation pattern, which contributes to AMOC weakening. Our results show that efforts to improve air quality, particularly around the Atlantic basin but also far away in East Asia, will contribute to future AMOC weakening.

Abstract. A variety of chemical and dynamical processes in the troposphere and stratosphere affect tropical total column ozone (TCO), the net effect of which may cause changes in surface UV radiation and impact human and ecosystem health. We use dynamical linear modeling to estimate tropical trends in TCO and partial column ozone (PCO) in the troposphere and three stratospheric layers to assess agreement between satellite observational composites and chemistry–climate model (CCM) simulations from two multi-model experiments (CCMI-1 and CCMI-2022). While both model experiments show tropical TCO increases over 2000–2021, CCMI–2022 trends (+2.5 DU) agree slightly better with observations than CCMI-1 (+1.6 DU). However, this overall agreement obscures multiple systematic differences in PCO trends between the models and observations across atmospheric layers. For example, since 2000 tropical tropospheric PCO increased significantly in CCMI-2022 (+1.5 DU) but not in CCMI–1 (+0.3 DU), largely explaining the difference in TCO trends. Also, despite nearly identical stratospheric PCO trends, CCMI-2022 trends are slightly more negative in the lower stratospheric (by ~0.5 DU), compensated by more positive middle/upper stratosphere trends compared to CCMI-1. Crucially, substantial differences exist across observational PCO trends, particularly in the troposphere and middle/upper stratosphere, and these disagreements limit the ability to evaluate CCM fidelity. Furthermore, while the inter-model correlation between late and early 21st century trends is suggestive of a potential emergent constraint on future ozone trends, the spread in observational trends precludes its observational implementation.

Anthropogenic aerosol and associated precursor gas emissions are already declining in many regions and are likely to decline significantly by 2050, with major implications for regional climate. Unlike greenhouse gases, aerosol impacts are spatially heterogeneous and can influence climate both near emission sources and through remote teleconnections. This is particularly important for the South Asian monsoon system, where both local and remote aerosol changes can significantly affect precipitation patterns. Using simulations from the Regional Aerosol Model Intercomparison Project, we examine how local and remote aerosol emission reductions influence South Asian climate across both pre-monsoon and monsoon seasons, including weakening of the elevated heat pump (EHP) mechanism during pre-monsoon months. Our analysis employs 10-member ensembles from 10 CMIP6-era models to compare three experiments with global, South Asian, and East Asian aerosol reductions relative to a high-emission baseline (SSP3-7.0). This experimental design allows us to isolate and quantify the distinct impacts of regional emission changes. Results reveal that global aerosol reductions produce a larger all-India precipitation increase ( +0.28 mm day -1) than South Asian reductions alone ( +0.19 mm day -1), with the strongest regional responses over the northern Bay of Bengal, the Western Ghats and Indo-Gangetic Plains. East Asian reductions show uncertain but modest precipitation reductions of 0.2-0.6 mmday-1 over parts of west-central and eastern Indian regions. Pre-monsoon carbonaceous aerosol reductions systematically weaken the EHP, cooling the mid-troposphere over the Himalayan foothills by up to 0.4 K and producing localised anomalous descent that opposes the climatological pre-monsoon ascent. Substantial inter-model diversity exists in the spatial patterns and magnitudes of these responses, highlighting key uncertainties in aerosol-monsoon interactions. The South Asian precipitation response is driven by enhanced land-sea thermal contrast, while the pre-monsoon EHP weakening is attributable exclusively to local South Asian carbonaceous aerosol forcing rather than remote teleconnections. These findings have direct implications for air quality and climate adaptation planning across South Asia as regional aerosol emissions diverge under different development pathways.

The representation of stratospheric transport in Chemistry-Climate Models (CCMs) is key for accurately reproducing and projecting the evolution of the ozone layer and other radiatively relevant trace gases. We evaluate stratospheric transport in CCMs that have participated in three model intercomparison initiatives (CCMVal-2, CCMI-1, and CCMI-2022) over the last similar to 15 years using modern satellite datasets and reanalyses. Key long-standing model biases persist across generations, with some worsening in recent simulations. Transport remains overly fast in the models, with a global mean age of air young bias of similar to 1 year for the CCMI-2022 median. It is argued that this bias could be associated with too fast tropical upwelling in the lower stratosphere and possibly to excessive vertical diffusion, with mixing biases being more uncertain. In the springtime southern polar stratosphere, the final warming is delayed (similar to 3 weeks), downwelling is underestimated (similar to 25 %), and the depth of the ozone minimum is overestimated (similar to 10 DU) on average in the most recent models. The tropopause is too high in all generations, and the tropical cold point tropopause is too warm in the latest generation (similar to 1-2 K). Long-term trends in transport over 1980-1999 are consistent across model generations and highlight the crucial role of ozone depletion in contributing to accelerate the Brewer-Dobson circulation and delaying the southern polar vortex breakdown.

Abstract Anthropogenic aerosol emissions are projected to decline rapidly in the near future as air quality regulations strengthen. Crucially, however, the response of large-scale atmospheric circulation to these reductions remains a major source of uncertainty. Here, we use multi-model ensembles from Regional Aerosol Model Intercomparison Project (RAMIP) to provide a diagnostic assessment of tropical circulation changes in response to global and regional aerosol reductions during 2015-2050. We find that global aerosol reductions lead to a poleward expansion of the Northern Hemisphere tropical width by 0.10° ± 0.08°, a weakening of the Northern Hemisphere Hadley Circulation by 1.77 ± 1.09 109 kg s-1 and a strengthening of the Southern Hemisphere Hadley Circulation by 2.53 ± 1.30 109 kg s-1. The Intertropical Convergence Zone (ITCZ) also shows a northward shift by 0.19° ± 0.10°. These meridional circulation changes consistently emerge across the regional experiments, with aerosol reductions over East Asia and North America+Europe contributing the most. Although the response of the zonal Pacific Walker circulation to global aerosol reductions is not statistically significant, models show a strengthening tendency that is significant under Africa+Middle East aerosol reductions. Notably, the ITCZ response to greenhouse gas forcing is weak and uncertain, whereas aerosol reductions produce a stronger and more robust response, even in the regional experiments. Our results suggest that both global and regional aerosol reduction significantly contribute to large-scale tropical circulation changes.

The Regional Aerosol Model Intercomparison Project (RAMIP) is designed to quantify the forcing and climate impacts of mid-21st century anthropogenic aerosol and precursor gas (AA) emissions reductions (both industrial and biomass burning), by comparing a weak (SSP3-7.0) versus strong (SSP1-2.6) level of air quality control aerosol emissions pathway. AA emissions reductions experiments include global (GLO), East Asia (EAS), South Asia, Africa and the Middle East (AFR), and North America and Europe (NAE). Here, we use RAMIP time-slice simulations with fixed sea surface temperatures and sea-ice distributions from nine models to quantify the aerosol effective radiative forcing (ERF), including aerosol radiation (ERFari) and aerosol cloud interactions (ERFaci). The multi-model global mean net ERFari+aci is 0.77 +/- 0.25 W m-2 for GLO, and three of the four regional perturbations yield a significant positive net ERFari+aci (up to 0.15 +/- 0.07 W m-2 for EAS). In all cases, net ERFari+aci is dominated by aerosol-cloud interactions, which are largely due to reduced cloud scattering. Of the four regions, NAE yields the largest forcing efficiency whereas AFR yields the weakest. Although the areas outside our four target regions contribute 25% to the GLO aerosol optical depth reduction, they disproportionately contribute 44% to the GLO net ERFari+aci. The multimodel regional mean net ERFari+aci for three regional perturbations is much larger (up to 1.64 +/- 1.36 W m-2 for EAS) than the corresponding global mean value. However, these regional values are even larger (up to 2.69 +/- 1.72 W m-2 for EAS) under global aerosol reductions, implying remote emission reductions represent a sizable contribution (up to 1.05 +/- 0.56 W m-2 for EAS). These large regional ERFs will in turn drive relatively large regional climate impacts, which continue to be underappreciated in most policy discussions.

Abstract. Many halocarbons are powerful greenhouse gases and also influence climate indirectly through depletion of stratospheric ozone which opposes their direct greenhouse effect. Changes in effective radiative forcing (ERF) from historical ozone depletion have been diagnosed from model experiments with perturbed halocarbons run under the sixth Coupled Model Intercomparison Project. This is more negative than the offline stratospheric-temperature-adjusted radiative forcing (SARF). Including effects of ozone depletion on the methane lifetime makes the historical net ERF of ozone depleting substances consistent with zero. The Integrated Ozone Depletion (IOD) metric has been used to apportion this ERF between the halocarbon species and thereby derive indirect 100-year Global Warming Potentials (GWP100s) for a suite of halocarbons. The indirect GWP100 for CFC-11 is enough to make the net GWP100 likely negative, whereas the indirect contribution for CFC-12 is smaller due to a combination of longer stratospheric lifetime and fewer chlorine atoms. use of the online ERF, rather than the offline SARF, allows the model physics to account for changes in stratospheric temperature (as well as tropospheric temperature, water vapour and clouds) rather than estimating stratosphere temperature changes using fixed dynamical heating. This online calculation of radiative forcing rather than offline leads to approximately double the indirect GWPs compared to World Meteorological Organization assessments. This formalism can be used with other estimates of ozone ERF, as the indirect GWPs scale linearly with this quantity.

Decreases in anthropogenic aerosols will reduce fine particulate matter (PM2.5); however, meteorological feedbacks alter dust emissions, modifying air quality gains. We use eight Earth System Models from the Regional Aerosol Model Intercomparison Project (RAMIP) simulations to assess African climate and air quality responses to anthropogenic aerosol emission perturbations, including meteorological feedbacks on dust emissions. By 2050, African and global emissions reductions drive the largest continent-average PM2.5 decrease (0.92 +/- 0.17 mu g m-3; 5% and 1.35 +/- 0.50 mu g m-3; 7%, respectively) relative to SSP3-7.0, though regional dust increases partially offset these reductions. Anthropogenic emissions reductions in the U.S. and Europe also lower African PM2.5 by 0.29 +/- 0.32 mu g m-3 (2%) due to teleconnections of Northern Hemisphere warming influencing the Intertropical Convergence Zone. Inter-model variability in dust and total PM2.5 reflects differences in meteorological responses and dust emission parameterizations. Meteorological responses explain 90% of dust emissions variability across regions. Aerosol-driven climate feedbacks on dust account for up to 70% of total PM2.5 changes in the Sahara and Namib, offsetting up to 20% of anthropogenic PM2.5 reductions across Africa. Under 2050 global and Africa-wide anthropogenic aerosol reductions, 96,000 (95% CI: 54,000-137,000) and 84,000 (95% CI: 43,000-125,000) PM2.5-related deaths are avoided in Africa, respectively. Dust PM2.5 contributes an uncertain 3.4% of the avoided deaths under global reductions and has no net effect under Africa-wide reductions. Aerosol-driven climate feedbacks may partially offset direct air quality gains, though their continental-scale contribution remains small and uncertain.

The North Atlantic Climate System Integrated Study (ACSIS) was a large multidisciplinary research programme funded by the UK's Natural Environment Research Council (NERC). ACSIS ran from 2016 to 2022 and brought together around 80 scientists from seven leading UK-based environmental research institutes to deliver major advances in the understanding of North Atlantic climate variability and extremes. Here, we present an overview of the data generated by the ACSIS programme. The datasets described cover the North Atlantic Ocean, the atmosphere above it (including its composition), and Arctic sea ice. Atmospheric composition datasets include measurements from seven aircraft campaigns (45 flights in total, 0–10 km altitude range) in the northeastern Atlantic (∼ 15–55° N, ∼ 40° W–5° E) made at intervals of 6 months to 2 years between February 2017 and May 2022. The flights measured chemical species (including greenhouse gases; ozone precursors; and volatile organic compounds – VOCs) and aerosols (organic aerosol – OA; SO4; NH4; NO3; and non-sea salt chloride – nss-Cl) (https://doi.org/10.5285/6285564c34a246fc9ba5ce053d85e5e7, FAAM et al., 2024). Ground-based stations at the Cape Verde Atmospheric Observatory (CVAO), Penlee Point Atmospheric Observatory (PPAO), and Plymouth Marine Laboratory (PML) recorded ozone, ozone precursors, halocarbons, greenhouse gases (CO2 and methane), SO2, and photolysis rates (CVAO; http://catalogue.ceda.ac.uk/uuid/81693aad69409100b1b9a247b9ae75d5, National Centre for Atmospheric Science et al., 2010); O3 and CH4 (PPAO, https://catalogue.ceda.ac.uk/uuid/8f1ff8ea77534e08b03983685990a9b0 (Plymouth Marine Laboratory and Yang, 2017); and aerosols (PML, https://doi.org/10.5285/e74491c96ef24df29a9342a3d57b5939, Smyth, 2024), respectively. Complementary model simulations of atmospheric composition were performed with the UK Earth System Model (UKESM1) for the period from 1982 to 2020 using Coupled Model Intercomparison Project Phase 6 (CMIP6) historical forcing up to 2014 and Shared Socioeconomic Pathways (SSP) scenario SSP3-7.0 from 2015 to 2020. Model temperature and winds were relaxed towards ERA reanalysis. Monthly mean model data for ozone, NO, NO2, CO, methane, stratospheric ozone tracers, and 30 regionally emitted tracers are available for download (https://data.ceda.ac.uk/badc/acsis/UKESM1-hindcasts, Abraham, 2024). ACSIS also generated new ocean heat content diagnostics (https://doi.org/10/g6wm, https://doi.org/10/g8g2, Moat et al., 2021a–b) and gridded temperature and salinity based on objectively mapped Argo measurements (https://doi.org/10.5285/fe8e524d-7f04-41f3-e053-6c86abc04d51 King, 2023). An ensemble of atmosphere-forced global-ocean sea-ice simulations using the NEMO-CICE model was performed with horizontal resolutions of 1/4 and 1/12° covering the period from 1958 to 2020 using several different atmosphere-reanalysis-based surface forcing datasets, supplemented by additional global simulations and stand-alone sea-ice model simulations with advanced sea-ice physics using the CICE model (http://catalogue.ceda.ac.uk/uuid/770a885a8bc34d51ad71e87ef346d6a8, Megann et al., 2021e). Output is stored as monthly averages and includes 3D potential temperature, salinity, zonal velocity, meridional velocity, and vertical velocity; 2D sea-surface height, mixed-layer depth, surface heat, and freshwater fluxes; ice concentration and thickness; and a wide variety of other variables. In addition to the data presented here, we provide a very brief overview of several other datasets that were generated during ACSIS and have been described previously in the literature.

This study assesses three different measures of radiative forcing (instantaneous: IRF; stratospheric-temperature adjusted: SARF; effective: ERF) for future changes in ozone. These use a combination of online and offline methods. We separate the effects of changes in ozone precursors and ozone-depleting substances (ODSs) and configure model experiments such that only ozone changes (including consequent changes in humidity, clouds and surface albedo) affect the evolution of the model physics and dynamics.In the Shared Socioeconomic Pathway 3-7.0 (SSP3-7.0) we find robust increases in ozone due to future increases in ozone precursors and decreases in ODSs, leading to a radiative forcing increase from 2015 to 2050 of 0.268 +/- 0.084 W m-2 ERF, 0.244 +/- 0.057 W m-2 SARF and 0.288 +/- 0.101 W m-2 IRF. This increase makes ozone the second largest contributor to future warming by 2050 in this scenario, approximately half of which is due to stratospheric ozone recovery and half due to tropospheric ozone precursors.Increases in ozone are found to decrease the cloud fraction, causing an overall negative adjustment to the radiative forcing (positive in the short wave but negative in the long wave). Non-cloud adjustments due to water vapour and albedo changes are positive. ERF is slightly larger than the offline SARF for the total ozone change but approximately double the SARF for the ODS-driven change (0.156 +/- 0.071 W m-2 ERF, 0.076 +/- 0.025 W m-2 SARF). Hence ERF is a more appropriate metric for diagnosing the climate effects of stratospheric ozone changes.

Under climate change driven by increased carbon dioxide (CO2) concentrations, stratospheric ozone will respond to temperature and circulation changes, leading to chemistry–climate feedback by modulating large-scale atmospheric circulation and Earth's energy budget. However, there is significant model uncertainty since many processes are involved and few models have a detailed chemistry scheme. This work employs the latest data from Coupled Model Intercomparison Project Phase 6 (CMIP6) to investigate the ozone response to increased CO2. We find that in most models, ozone increases in the upper stratosphere (US) and extratropical lower stratosphere (LS) and decreases in the tropical LS; thus, the total column ozone (TCO) response is small in the tropics. The ozone response is mainly driven by slower chemical destruction cycles in the US and enhanced upwelling in the LS, with a highly model-dependent Arctic ozone response to polar vortex strength changes. We then explore the ozone–climate feedback by combining offline calculations and comparisons between models with (“chem”) and without (“no-chem”) interactive chemistry. We find that the stratospheric temperature response is substantial, with a global negative radiative forcing ranging from −0.03 to −0.19 W m−2. We find that chem models consistently simulate less tropospheric warming and a stronger weakening of the polar stratospheric vortex, which result in a larger increase in sudden stratospheric warming (SSW) frequency than in most no-chem models. Our findings show that ozone–climate feedback is essential for the climate system and should be considered in the development of Earth system models.

Lower stratospheric ozone between 60°S and 60°N has continued to decline since 1998, despite the reduction of ozone‐depleting substances following the Montreal Protocol. Previous studies have shown that, while chemistry‐climate models reproduce the negative ozone trend in the tropical lower stratosphere as a response to increased upwelling, they fail to capture the ozone decline in northern midlatitudes. This study revisits recent lower stratospheric ozone trends over the period 1998–2018 using two types of simulations from the new Chemistry Climate Model Initiative 2022 (CCMI‐2022): REF‐D1, with observed sea surface temperatures, and REF‐D2, with simulated ocean. The observed negative trend in midlatitudes falls within the range of model trends, especially when considering simulations with observed boundary conditions. There is a large spread in the simulated midlatitudes ozone trends, with some simulations showing positive and others negative trends. A multiple linear regression analysis shows that the spread in the trends is not explained by the different linear response to external forcings (solar cycle, global warming, and ozone‐depleting substances) or to the main variability modes (El Niño‐Southern Oscillation and the quasi‐biennial oscillation) but is instead attributed to internal atmospheric variability. Moreover, the fact that some models show very different trends across members, while other models show similar trends in all members, suggests fundamental differences in the representation of the internal variability of ozone transport across models. Indeed, we report substantial intermodel differences in the ozone‐transport connection on interannual timescales and we find that ozone trends are closely coupled to transport trends.

The transport of ozone from the stratosphere to the troposphere is a key contributor to the tropospheric ozone budget. It is estimated that the stratosphere-to-troposphere flux of ozone (STT) leads to ~500 Tg of ozone transported into the troposphere each year, which is comparable to the net chemical production of ozone within the troposphere. We will present an analysis of the tropospheric ozone budget in the CCMI2022 experiments performed with UKESM-StratTrop, a whole atmosphere chemistry-climate model. We focus on the specified dynamics experiments covering 1982-2018, during which there was significant ozone depletion. We intercompare the ozone budget from the derived using the complementary approaches of Ox and Oy species, and use idealised tracers to examine in detail the role of stratosphere-to-troposphere transport on tropospheric composition. Where possible, these model simulations are compared with in-situ calculation of ozone production and loss rates derived from observations.

Global surface warming has accelerated since around 2010, relative to the preceding half century1, 2-3. This has coincided with East Asian efforts to reduce air pollution through restricted atmospheric aerosol and precursor emissions4,5. A direct link between the two has, however, not yet been established. Here we show, using a large set of simulations from eight Earth System Models, how a time-evolving 75% reduction in East Asian sulfate emissions partially unmasks greenhouse gas-driven warming and influences the spatial pattern of surface temperature change. We find a rapidly evolving global, annual mean warming of 0.07 +/- 0.05 degrees C, sufficient to be a main driver of the uptick in global warming rate since 2010. We also find North-Pacific warming and a top-of-atmosphere radiative imbalance that are qualitatively consistent with recent observations. East Asian aerosol cleanup is thus likely a key contributor to recent global warming acceleration and to Pacific warming trends.

Rising greenhouse gases (GHG) and decreasing anthropogenic ozone-depleting substances (ODS) are the main drivers of stratospheric climate evolution in the 21st century. However, our understanding of the coupling between stratospheric composition, radiation and dynamics is still a subject to many uncertainties, partly because of the simplified representation of ozone in many current climate models. In our work, we study stratospheric ozone-climate interactions using idealized CMIP6 DECK experiments (pre-industrial control, abrupt quadrupling of CO2, and 1 % yr−1 CO2 increase). This set up provides longer time-series and stronger GHG forcing than in the historical period. The 6th phase of CMIP has a larger number of participating models with interactive chemistry (“CHEM”) to be contrasted against the models where it is prescribed (“NOCHEM”) than in previous generations of CMIP models. Our findings show that CMIP6 models broadly exhibit a similar ozone response to CO2 with increased ozone in the upper stratosphere (US), driven mostly by rapid adjustments (chemistry), and slow transport-driven decrease in the tropical lower stratosphere (LS), and increase in the extratropical LS. The total column ozone response is small in the tropics and positive at high latitudes, with large inter-model discrepancy, possibly arising from model biases in polar vortex dynamics. We also quantify, for the first time, the radiative and dynamical impacts of ozone and quantify their inter-model uncertainty, by means of radiative transfer calculations and careful comparison of chem vs nochem models. First, we find that CHEM models are colder than NOCHEM models in the UTLS region, consistent with the ozone changes in these regions. Second, we find that the large-scale circulation response is systematically different in CHEM and NOCHEM. Lastly, climate sensitivity tends to be lower in CHEM than NOCHEM models, although the uncertainty across models is large and processes that are not tied to ozone cannot be ruled out. Taken together, our work demonstrates that ozone changes can potentially modulate the modeled response to elevated CO2 levels, stressing the importance of interactive chemistry in the future generation of models, in order to correctly simulate the coupling between chemistry, radiative and dynamical processes under climate change.