While explosive volcanic eruptions cause ozone loss in the current atmosphere due to an enhancement in the availability of reactive chlorine following the stratospheric injection of sulfur, future eruptions are expected to increase total column ozone as halogen loading approaches preindustrial levels. The timing of this shift in the impact of major volcanic eruptions on the thickness of the ozone layer is poorly known. Modeling four possible climate futures, we show that scenarios with the smallest increase in greenhouse gas concentrations lead to the greatest risk to ozone from heterogeneous chemical processing following future eruptions. We also show that the presence in the stratosphere of bromine from natural, very short‐lived biogenic compounds is critically important for determining whether future eruptions will lead to ozone depletion. If volcanic eruptions inject hydrogen halides into the stratosphere, an effect not considered in current ozone assessments, potentially profound reductions in column ozone would result.

The ozone layer is essential for the existence of life on Earth. Due to the human release of chlorine‐containing chemicals such as chlorofluorocarbons into the atmosphere in the twentieth century, a large volcanic eruption occurring today would initiate chemical reactions that reduce the thickness of the ozone layer. In the future, when atmospheric levels of chlorine have fallen, large volcanic eruptions are instead expected to increase the thickness of the ozone layer, but important details relevant to this shift in volcanic impact are poorly known. We use a computer model to simulate a large volcanic eruption in four different climate change futures, finding that optimistic scenarios with lower greenhouse gas (GHG) emissions result in greater potential losses of ozone following an explosive volcanic eruption than scenarios with more GHG emissions. In the coming decades, the stratospheric presence of bromine supplied by natural, very short‐lived compounds makes the ozone layer more susceptible to loss following volcanic eruptions than if this halogen source were not present. If HCl, a chlorine‐containing compound often present in large quantities in volcanoes, were to reach the stratosphere following a future explosive eruption, substantial ozone loss could result, regardless of the year in which the eruption occurred.

1 Introduction The atmosphere is currently in a temporal window of elevated halogen loading due to the anthropogenic release of chlorofluorocarbons and halons during the twentieth century. Large explosive volcanic eruptions that inject sulfur‐bearing compounds into the stratosphere during this period are expected to produce significant ozone depletion from the heterogeneous chemical processing of halogen species, as was observed in the Northern Hemisphere in the years following the 1991 eruption of Mount Pinatubo [e.g., Pitari and Rizi, 1993; Kinnison et al., 1994; Solomon et al., 1996; World Meteorological Organization (WMO), 2014]. In the future when anthropogenic halogen concentrations have recovered to near preindustrial levels, it is widely accepted that heterogeneous chemical perturbations following volcanic eruptions will have the opposite effect, enhancing the thickness of the ozone layer [Tie and Brasseur, 1995; Rosenfield, 2003; WMO, 2014]. However, important factors central to the timing and evaluation of the sensitivity of ozone to volcanic eruptions have not previously been evaluated. Here we present results from an extensive modeling study that quantifies the risks to stratospheric ozone from explosive volcanic eruptions for four future climate scenarios, including for the first time a sensitivity analysis of the effect on ozone of bromine supplied to the stratosphere by the decomposition of naturally occurring, very short‐lived (VSL) biogenic compounds. We also explore the implications for ozone resulting from the direct stratospheric injection of hydrogen halides by a volcanic eruption in contemporary and future atmospheres. Though the eruption of Mount Pinatubo remains the canonical case study of the impact of volcanic aerosol on the ozone layer due to the large quantity of associated in situ and remote sensing data, the eruption occurred in an exceptionally wet environment caused by the coincidental transit of a tropical cyclone [Tupper et al., 2005]. As a result, the chemical partitioning of water‐soluble halogen species within the eruption column was unusually perturbed, producing a stratospheric volcanic cloud that was highly depleted in hydrogen halides [Mankin et al., 1992; Tabazadeh and Turco, 1993]. 1.1 Volcanic Injection of Sulfate Eruption columns from explosive volcanism provide conduits for the efficient transport of massive quantities of degassed volatiles to the lower‐to‐middle stratosphere over very short time periods [Textor et al., 2003]. Although explosive volcanic events of stratospheric significance are relatively infrequent, occurring every 5.5 years on average [Grainger and Highwood, 2003], they are remarkable in their impact on the trace gas composition of the stratosphere. The enhanced loading of stratospheric sulfuric acid aerosol, produced from the oxidative processing of volcanic SO 2 , provides surface area for the conversion of catalytically inactive halogen species to their active forms and can also induce global climatological changes in radiative forcing and atmospheric dynamics [Kinne and Toon, 1992; Minnis et al., 1993; Pitari and Rizi, 1993; Shepherd et al., 2014]. Volcanic perturbations of stratospheric aerosol exert contrasting effects on ozone in different chemical environments [Kinnison et al., 1994; Tie and Brasseur, 1995; Al‐Saadi et al., 2001; Aquila and Oman, 2013; WMO, 2014; Berthet et al., 2017]. In the middle stratosphere, enhancement in the rate of heterogeneous reactive uptake of N 2 O 5 results in a suppression of the catalytic odd‐nitrogen destruction of ozone. Conversely, in the lower stratosphere, enhanced activation rates of halogen reservoirs such as chlorine nitrate and hydrogen chloride produce an intensification in reactive halogen‐induced ozone destruction. The net impact on column ozone is a function of many factors, including halogen availability (equivalent effective stratospheric chlorine (EESC), which includes chlorine and weighted bromine contributions), halogen sink abundance, aerosol injection mass distribution, and stratospheric temperature. As a result, in the contemporary stratosphere, lower stratospheric chemistry dominates that of the middle stratosphere and forces net reduction of total column ozone in response to enhanced surface area following a major volcanic eruption. In future scenarios of low anthropogenic halogen loading, Pinatubo‐like eruptions, defined here as volcanic eruptions in which only SO 2 is injected into the stratosphere, are expected to cause net increases in total column ozone as middle stratospheric effects on odd‐nitrogen outweigh lower stratospheric halogen chemistry [Tie and Brasseur, 1995; Rosenfield, 2003; Pitari et al., 2014; WMO, 2014]. Past attempts to identify the inflection point at which the response of total column ozone to heterogeneous chemistry on volcanic sulfate aerosol switches from net depleting to net enhancing are highly uncertain, ranging from 2015 to an indeterminate date after 2040 [Tie and Brasseur, 1995; Rosenfield, 2003]. However, these studies did not consider the supply of stratospheric bromine by VSL biogenic species, which are now known to play a significant role in the photochemistry of the lower stratosphere [WMO, 2014]. A more recent model intercomparison study of geoengineering scenarios that does include VSL bromine [Pitari et al., 2014] determines that this shift may occur after 2050 but differs from our simulations of explosive volcanism with regard to total aerosol loading, temporal profile of mass injection, injection latitude, injection mass vertical distribution, and inclusion of radiative‐dynamic effects. 1.2 Volcanic Injection of Halogens Explosive volcanoes often emit large quantities of hydrogen halides, particularly HCl, but these halogens can be removed by hydrometeors (e.g., rainwater and ice) in the troposphere before they ascend to the stratosphere and lead to ozone destruction [Tabazadeh and Turco, 1993]. A number of recent publications [Kutterolf et al., 2013, 2015; Cadoux et al., 2015; Vidal et al., 2016], however, have shown that significant stratospheric halogen injection may accompany explosive volcanic eruptions. Once dismissed as highly improbable, this effect is not considered in current ozone assessments [WMO, 2014]. Despite highly efficient hydrometeor scavenging of hydrogen halides in volcanic eruption columns, the direct injection of significant quantities of volcanic halogens into the stratosphere is nonetheless predicted by theory [Textor et al., 2003; Gutiérrez et al., 2016] and has been confirmed via remote sensing [Carn et al., 2016], in situ observation [Mankin and Coffey, 1984; Hunton et al., 2005; Millard et al., 2006; Rose et al., 2006], and ice core analysis [Zdanowicz et al., 1999; De Angelis et al., 2003]. Estimates of volcanic hydrogen halide emissions from the historical record vary greatly, frequently exceeding several tens of teragrams of HCl in addition to many hundreds of gigagrams of HBr following a large explosive eruption [Kutterolf et al., 2013, 2015; Cadoux et al., 2015; Vidal et al., 2016], though the quantity transported to the stratosphere is generally attenuated [Tabazadeh and Turco, 1993]. A lower boundary for the stratospheric injection efficiency of halogens within an eruption column is provided by the exceptional case of Mount Pinatubo (15.1°N), in which the aforementioned tropical cyclone directly transited the paroxysmal eruption plume [Tupper et al., 2005] and scrubbed nearly the entirety of the 4.5 Tg of HCl estimated to have degassed [Westrich and Gerlach, 1992; Mankin et al., 1992]. Conversely, case studies have quantified that the majority of the halogen mass emitted by an eruption of Hekla (64.0°N) in the year 2000 reached the stratosphere [Millard et al., 2006; Rose et al., 2006]. Moderate stratospheric inputs of HCl have often been observed; Aura Microwave Limb Sounder (MLS) recorded stratospheric HCl:SO 2 ratios of 0.01–0.03 (relative mixing ratios) for 14 eruptions spanning the years of 2005 to 2014 [Carn et al., 2016]. Additionally, ratios of 0.06–0.15 have been estimated from the ice core record of the much larger 7.7 kya eruption of Mount Mazama (42.9°N) [Zdanowicz et al., 1999]. For perspective, the increase in stratospheric inorganic chlorine from Mount Mazama was estimated to be 8.5 ppbv [Zdanowicz et al., 1999], a remarkable 4 times greater than the entire stratospheric mixing ratio of chlorine in 1980 (i.e., immediately prior to the major human‐driven increase). 1.3 Overview The present study uses the AER‐2D model [Weisenstein et al., 1997; Salawitch et al., 2005; Thomason and Peter, 2006; Weisenstein et al., 2007; Sheng et al., 2015] to quantify the primary chemical factors determining whether future volcanism will enhance or deplete column ozone. First, we quantify how Pinatubo‐like eruptions will alter total column ozone in contemporary and future atmospheres, as defined by the Representative Concentration Pathway (RCP) emissions projections of greenhouse gases (GHGs) and halocarbons [Meinshausen et al., 2011]. For each climate scenario, we consider a range of VSL bromine mixing ratios in the lower stratosphere. We then evaluate the future response of column ozone to stratospheric injection of volcanic halogens, using realistic HCl:SO 2 ratios. Volcanic HBr is not simulated due to the paucity of observational data. Modeled injection conditions (e.g., mass distribution and temporal profile) are based on the parameters previously determined within the AER‐2D model that were required to reproduce both the observed Mount Pinatubo Northern Hemispheric ozone losses and the best fit volcanic aerosol distribution in the model years following 1991 [Salawitch et al., 2005; Thomason and Peter, 2006; Sheng et al., 2015].

2 Methods The AER‐2D chemical‐transport‐aerosol model [Weisenstein et al., 1997, 2007] was selected for this work due to its extensive prior use in studies of the 1991 Mount Pinatubo eruption [e.g., Salawitch et al., 2005; Thomason and Peter, 2006; Arfeuille et al., 2013; Sheng et al., 2015] and its benchmark performance treating stratospheric aerosol of volcanic origin in model intercomparison studies [Thomason and Peter, 2006]. The model is fully prognostic with regard to aerosol evolution, employing 40 sectional size bins along with nucleation, coagulation, condensation/evaporation, sedimentation, and heterogeneous chemical interactions. We simulate the transport and chemistry of volcanic clouds of varying composition using prescribed temperature and transport fields with a focus on the effects of heterogeneous chemistry on total column ozone over a grid of 19 latitudes (90°S–90°N) and 51 pressure levels (1000–0.2 hPa). Initial conditions for each eruption experiment were established after spin‐up to model stability at the relevant boundary conditions for the specified simulation years. A total of 264 model scenarios were evaluated over 2600 model years. All column ozone deviations reported in this work were calculated as percentage differences from scenarios in which no volcanic input was allowed, but all other conditions were identical; i.e., the reported changes in ozone are due only to the volcanic perturbation. For experiments in which volcanic input occurred, SO 2 vertical mass distribution was parameterized according to the optimal distribution of Sheng et al. [2015]. Using this vertical distribution, we performed a sensitivity study to determine the mass input required to reproduce the observed 1991 Mount Pinatubo northern midlatitude ozone anomalies [Solomon et al., 1996; Angell, 1997; Salawitch et al., 2005] under prescribed climatological fields representative of the historical 1990s [Fleming et al., 1999]. SO 2 injections between 7 and 17 Tg provided acceptable matches; the lowest eruption mass, 7 Tg SO 2 , was selected for further experimentation as our Pinatubo‐scale injection mass as it provides good agreement with the observed response within the model framework and minimizes the impact of radiative‐dynamical effects discussed below. Volcanic clouds may perturb the Brewer‐Dobson Circulation in addition to repartitioning chemical inventories. This effect can either enhance or deplete column ozone thickness, depending on latitude and climatological conditions [Kinne and Toon, 1992; Rozanov et al., 2002; Telford et al., 2009; Shepherd et al., 2014]. The magnitude of the radiative‐dynamical perturbation on the ozone anomaly has been demonstrated to be proportional to the mass of the stratospheric injection of SO 2 [Dhomse et al., 2014; Muthers et al., 2015]; larger, more explosive injections tend to induce more pronounced dynamical changes resultant from radiative heating. Though the AER‐2D model does not capture these volcanically induced modifications to atmospheric transport effects, it provides a comprehensive analysis of the chemical response. As stated, to minimize the impact of radiative‐dynamical effects in this study, we utilize a SO 2 injection mass of 7 Tg. The 2 year average global ozone anomaly resultant from radiative heating and subsequent dynamical perturbations expected from an injection of this mass was estimated by extrapolation of the SO 2 mass sensitivity study of Muthers et al. [2015]. The value obtained from the extrapolation, +0.7 DU (~0.2%), was found to be less than the reported global‐temporal average ozone anomalies for all simulated eruptions in this work except for the year 2100 RCP 6.0 scenario with 4 pptv VSL bromine. Greenhouse gas and long‐lived halocarbon chemical boundary conditions were obtained from the RCP emissions projections of Meinshausen et al. [2011]. Historical average (1978–2004) climatological transport fields were employed in all cases [Fleming et al., 1999]. Temperature fields were obtained from MIROC‐CHEM‐ESM [Watanabe et al., 2011], an Earth system model with stratospheric chemistry, and employed for the RCP future and contemporary scenarios.

3 Results and Discussion Figures 1a–1e present the modeled progression of total column ozone sensitivity following a Pinatubo‐like eruption in contemporary and future scenarios as a function of latitude and time (main panels), as a function of latitudinal averages and time (top subpanels), as a function of time averages and latitude (right subpanels), and as a single 4 year global‐temporal average (top right boxes). For each panel, atmospheric conditions are defined by RCP 6.0 projections [Meinshausen et al., 2011] of anthropogenic halogen and GHG mixing ratios, supplemented with 4 pptv bromine from very short‐lived sources; VSL bromocarbons are known to contribute 4–10 pptv to stratospheric inorganic bromine loading [Salawitch et al., 2005, 2010; Liang et al., 2014; Werner et al., 2017]. The values of EESC are shown below each panel, determined per Newman et al. [2007]. As EESC decreases due to the decay of anthropogenic halogen sources over the remainder of this century, the sensitivity of column ozone to volcanic aerosol attenuates, as would be expected. Modest regional enhancements in column ozone begin to appear in 2061, with the interhemispheric differences in ozone response primarily because the simulated volcanic injection occurred in the northern tropics and produced an aerosol mass asymmetry across the hemispheres. Globally, there is still significant net loss of total column ozone beyond modeled year 2071. Our results indicate that the ozone column remains vulnerable to Pinatubo‐like volcanic eruptions decades longer than previously projected [Tie and Brasseur, 1995; Rosenfield, 2003; WMO, 2014]. Figure 1 Open in figure viewer PowerPoint Newman et al. [ 2007 Ozone response to Pinatubo‐like eruptions in contemporary and future atmospheres. RCP 6.0 scenarios including 4 pptv VSL bromine are simulated for (a) 2018, (b) 2051, (c) 2061, (d) 2071, and (e) 2101. Global averages (90°S–90°N) of total column ozone perturbation are traced atop each panel as a function of time. Temporal average ozone anomalies are traced right. Global‐temporal averages are enumerated in the top right. Black triangles indicate injection latitude and time. Red colors indicate column ozone depletion, and blue colors indicate column ozone enhancement. EESC values are presented for 3 year old air parcels, determined per], with an additional EESC contribution from the inclusion of 4 pptv VSL bromine. The details of the future response of total column ozone to Pinatubo‐like eruptions vary greatly between RCP scenarios for GHGs. We explore long‐range ozone sensitivity to volcanic perturbation using all four RCP projections for year 2101 in Figures 2a–2d, assuming 4 pptv VSL bromine is present in the stratosphere. Total integrated ozone perturbations span from small global depletions within RCP 2.6 (with much more significant localized ozone losses) to marginal enhancements in global column ozone under the conditions of RCP 8.5 (with both localized ozone gains and losses). Differences in stratospheric temperature, methane, nitrous oxide, and background EESC drive these divergent responses between the RCP scenarios; methane and nitrous oxide mixing ratios tend to increase as the scenarios progress from RCP 2.6 to RCP 8.5, while average stratospheric temperatures decrease. Changes in stratospheric temperatures account for the majority of the variation in the response of ozone between the four RCP scenarios due to the impact of temperature on the reaction kinetics. For example, if we run the model with chemical boundary conditions corresponding to RCP 8.5 but use the warmer RCP 2.6 temperature fields, we observe global‐temporal ozone losses of −0.8%, rather than the ozone production shown in Figure 2d. In addition, differences in future methane mixing ratios account for a large portion of the remaining variation between the RCP scenarios because methane reacts with Cl radicals in the stratosphere to terminate the ozone loss cycle. Figure 2 Open in figure viewer PowerPoint Newman et al. [ 2007 Ozone response to a Pinatubo‐like eruption in year 2101 for different RCP scenarios and VSL bromine levels. (a–d) Pinatubo‐like eruptions in the year 2101 for each RCP scenario with 4 pptv VSL bromine. Global averages (90°S–90°N) of column ozone perturbation are traced atop each panel as a function of time. Temporal average ozone anomalies are traced right. Global‐temporal averages are enumerated in the top right. Black triangles indicate injection latitude and time. (e–i) An eruption is simulated (year 2101, RCP 6.0) with background VSL bromine mixing ratios ranging from 0 to 8 pptv (indicated above each panel). (j) Latitudinally averaged ozone column changes versus time for scenarios in Figures 2 e– 2 i, (k) Latitude versus temporally averaged column deviations for scenarios in Figures 2 e– 2 i. EESC values are presented for 3 year old air parcels, determined per], with additional EESC contributions from the inclusion of VSL bromine. The primary determinant of future ozone response to a volcanic eruption within any specified RCP emission scenario in the year 2101 is VSL bromine from biogenic sources. This sensitivity mainly arises from the increasing contribution of bromine to the overall halogen loading of the modeled lower stratosphere. Figures 2e–2k illustrate the mode change induced when varying VSL bromine from 0 to 8 pptv within RCP 6.0. These scenarios are identical in all parameters except for VSL bromine. Global‐temporal average column ozone depletions/enhancements are enumerated in each panel. Model runs in which VSL bromine is neglected or set to a small value result in volcanic enhancement of total column ozone, especially in the midlatitudes, where the efficiency of N 2 O 5 hydrolysis is highest. Using more realistic values of VSL bromine in the stratosphere, however, column ozone remains susceptible to volcanic‐aerosol‐induced ozone depletion through the beginning of the next century. Figures 2j–2k provide time‐resolved and latitude‐resolved column ozone responses for the VSL bromine scenarios. When halogens are coinjected with sulfate into the stratosphere following explosive volcanic eruptions, we predict significant depletion of stratospheric ozone. This is true for both modest partitioning (0.014 HCl:SO 2 , as in the recent MLS record [Carn et al., 2016]), and more substantial partitioning (0.14 HCl:SO 2 , as for Mount Mazama [Zdanowicz et al., 1999]) of hydrogen halides into the stratosphere. These cases are presented in Figure 3 within the RCP 6.0 emissions framework, including 4 pptv VSL bromine, for the eruption years of 2018 and 2101. Figures 3a and 3b, 3c and 3d, and 3e and 3f correspond to HCl:SO 2 mixing ratios of 0, 0.014, and 0.14, respectively. For both contemporary and future simulations, stratospheric halogen injection induces a substantial reduction of total column ozone. For example, injected gas ratios of 0.14 HCl:SO 2 enhance 4 year average column ozone depletions at northern midlatitudes (30°–60°N), relative to injection of SO 2 alone, by a factor of 3 in the contemporary scenario and by a factor of 17 in the year 2101. While the magnitude of ozone depletion following volcanic coinjection of SO 2 and HCl is greater in the contemporary period due to high anthropogenic halogen loading, in the future scenario, halogens originating from volcanic eruptions represent a much greater fraction of the total background EESC. Accordingly, column ozone becomes more sensitive to volcanic halogen injection as anthropogenic halogen loading declines. Though results for RCP 6.0 are shown, large ozone depletion is found in all four RCP scenarios over all modeled years when significant hydrogen halides are coinjected with SO 2 following an explosive volcanic eruption. Figure 3 Open in figure viewer PowerPoint Ozone response to stratospheric halogen injection in contemporary and future atmospheres. (a and b) Pinatubo‐like eruptions (SO 2 injection only), (c and d) coinjection of 0.014 HCl:SO 2 (EESC effectively increased by ~0.3 ppbv), and (e and f) coinjection of 0.14 HCl:SO 2 (EESC effectively increased by ~3 ppbv). Note that the color scale is nonlinear in order to encompass the broad range of ozone changes. Global averages (90°S–90°N) of total column ozone perturbation are traced atop each panel as a function of time. Temporal average ozone anomalies are traced right. Global‐temporal averages are enumerated in the top right. Black triangles indicate injection latitude and time.

4 Conclusions We find that the vulnerability of the atmosphere to column ozone reductions following Pinatubo‐like eruptions (SO 2 only) will continue into the late 21st century, significantly later than prior estimates [Tie and Brasseur, 1995; Rosenfield, 2003; WMO, 2014]. The magnitude of the expected ozone response is dependent on the GHG loading of the atmosphere, with the largest potential ozone losses occurring for future climate scenarios with the smallest increase in GHGs. The differences between the future climate scenarios following a volcanic eruption are primarily driven by variations in projected stratospheric temperature, as well as future levels of methane. For late 21st century Pinatubo‐like eruptions, after background chlorine loading is reduced, VSL bromine levels primarily dictate whether column ozone will be enhanced or depleted. More VSL bromine results in larger modeled ozone depletion. This effect is dominant regardless of the projected RCP emissions scenario. When the strong sensitivity of the ozone response to small enhancements in bromine mixing ratios is juxtaposed with the large uncertainty in current and projected future lower stratospheric VSL bromocarbon fluxes, an investigational priority is evident. Despite highly efficient scrubbing of halogens within eruption columns, the historical record indicates the potential for future volcanic eruptions to substantially enhance the halogen loading of the stratosphere [Zdanowicz et al., 1999; Kutterolf et al., 2013, 2015; Cadoux et al., 2015; Vidal et al., 2016]. The model calculations presented indicate that Pinatubo‐sized eruptions with moderate stratospheric HCl:SO 2 injection ratios would likely cause a significant reduction of total column ozone even after anthropogenic halogens have decayed to mid‐twentieth century levels. The dramatic future ozone losses modeled here for the larger 0.14 HCl:SO 2 injection ratio are consistent with recent calculations of years‐long, extreme reductions of midlatitude column ozone from historic eruptions in preindustrial atmospheres [Black et al., 2014; Cadoux et al., 2015]. The implications for surface life on Earth from such a future volcanic eruption could be profound regardless of anthropogenic halogen loading should such an eruption occur. Though we do not model the additional coinjection of bromine or iodine compounds with HCl and SO 2 , the sparse record of measurements indicates that the concentrations and fate of these halogens in volcanic gases could be of stratospheric significance [Bureau et al., 2000; Snyder and Fehn, 2002; Aiuppa et al., 2009; Kutterolf et al., 2013, 2015]. The coinjection of bromine and/or iodine with chlorine would likely result in even more extreme ozone reductions following a halogen‐rich eruption due to the significantly greater ozone depletion efficiencies of bromine and iodine relative to chlorine.

Acknowledgments We gratefully acknowledge funding from the National Aeronautics and Space Administration (NASA) through grants: NNX15AD87G (D.M.W. and J.E.K.), NNX15AF60G (J.G.A., D.M.W., and J.E.K.), and NNX14AF19G (R.J.S.). We thank Stephen Leroy for the provision of additional computational resources and Michael Tighe and Jordan Wilkerson for helpful discussions. For our use of RCP temperature fields, we acknowledge the World Climate Research Programme's Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the Japan Agency for Marine‐Earth Science and Technology, Atmosphere and Ocean Research Institute (The University of Tokyo), and National Institute for Environmental Studies. Data generated and evaluated in the preparation of this work are publicly available on the Harvard Dataverse (https://dataverse.harvard.edu/dataverse/Klobas). The authors declare no competing financial interests.