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Reconciling the Climate and Ozone Response to the 1257 CE Mount Samalas Eruption

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Reconciling the Climate and Ozone Response to the 1257 CE Mount Samalas Eruption Reconciling the climate and ozone response to the 1257 CE Mount Samalas eruption David C. Wadea, Céline M. Vidalb, N. Luke Abrahama,c, Sandip Dhomsed, Paul T. Griffithsa,c, James Keeblea,c, Graham Mannd, Lauren Marshalla, Anja Schmidta,b, and Alexander T. Archibalda,c,1 aCentre for Atmospheric Science, Department of Chemistry, Lensfield Road, Cambridge, CB2 1EW, UK; bDepartment of Geography, Downing Place, Cambridge, CB2 3EN, UK; cNational Centre for Atmospheric Science, Department of Chemistry, Lensfield Road, Cambridge, CB2 1EW, UK; dSchool of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK This manuscript was compiled on September 1, 2020 1 The 1257 CE eruption of Mount Samalas (Indonesia) is the source of ies have investigated the climate response to the 1257 Mt. 21 2 the largest stratospheric injection of volcanic gases in the Common Samalas eruption. However, when compared with observa- 22 3 Era. Sulfur dioxide emissions produced sulfate aerosols that cooled tions or proxy-records (11–13), most previous simulations 23 4 Earth’s climate with a range of impacts on society. The co-emission overestimate the surface cooling response to Mt. Samalas, and 24 5 of halogenated species has also been speculated to have led to wide- other large eruptions (14). Despite the 1257 eruption of Mt. 25 6 scale ozone depletion. Samalas emitting 1.8× more SO2 than the 1815 eruption of 26 7 Here we present simulations from HadGEM3-ES, the first fully- Mt. Tambora, the Northern Hemisphere temperature response, 27 8 coupled Earth system model, with interactive atmospheric chemistry reconstructed by tree-ring maximum latewood density (MXD) 28 9 and a microphysical treatment of sulfate aerosol, used to assess the methods, is relatively similar (7, 8). This has been a puzzle 29 10 chemical and climate impacts from the injection of sulfur and halo- for the climate modeling community. Timmreck et al. (15) 30 11 gen species into the stratosphere as a result of the Mt. Samalas and Stoffel et al. (8) were able to simulate a broad agreement 31 12 eruption. Whilst our model simulations support a surface air temper- between their Atmosphere Ocean General Circulation Model 32 13 ature response to the eruption of the order of -1°C, performing well (AO-GCM) simulations and tree-ring based reconstructions, 33 14 against multiple reconstructions of surface temperature from tree- but Stoffel et al. have shown that the surface temperature 34 15 ring records, we find little evidence to support significant injections response was very sensitive to the assumed eruption month 35 16 of halogens into the stratosphere. and the height of injection (8), whilst Timmreck et al. found 36 17 Including modest fractions of the halogen emissions reported from that the size of the prescribed aerosol effective radii were very 37 18 Mt. Samalas leads to significant impacts on the composition of the important (15). 38 19 atmosphere and on surface temperature. As little as 20% of the halo- Both the changes in aerosol number concentrations and 39 20 gen inventory from Mt. Samalas reaching the stratosphere would re- size and gas-phase composition (chemistry) are important 40 21 sult in catastrophic ozone depletion; extending the surface cooling aspects of the role of large injections of sulfur (like those 41 22 caused by the eruption. However, based on available proxy-records from Mt. Samalas) on climate (16, 17). Changes in aerosol 42 23 of surface temperature changes, our model results support only very properties and changes in chemistry are strongly coupled. 43 24 minor fractions (1%) of the halogen inventory reaching the strato- Large eruptions, like Mt. Samalas, can inject their volatile 44 25 sphere and suggest that further constraints are needed to fully re- gases into the stratosphere. In this region, volcanic sulfate 45 26 solve the issue. Samalas | Climate | Ozone | Modeling Volcanic Impacts Significance Statement 1 The eruption of Mount Samalas in 1257 (Indonesia),DRAFT with The Mount Samalas eruption in 1257, one of the largest ex- 2 Volcanic Explosivity Index (VEI) 7, was identified by Lavigne plosive volcanic eruptions in the Common Era, has proven 3 et al. (1) as the source of the largest sulfate spike of the a complex case for climate models – which have generally 4 Common Era in both Greenland and Antarctica ice cores overestimated the climate response compared with proxy data. 5 (2, 3). Analyses of erupted products and their melt inclusions Here we perform the first Earth system model simulations of 6 suggests that the eruption released 158±12 megatons (Tg) of the impacts of the Mount Samalas eruption using a range of 7 sulfur dioxide (SO2), together with 227±18 Tg of chlorine (Cl) SO2 and halogen emission scenarios. Reported halogen emis- 8 and up to 1.3 Tg of bromine (Br) (4); making it responsible sions are considerable from the eruption but using our model 9 for the emissions of the greatest quantity of volcanic gases into simulations and reconstructed climate response we can rule 10 the stratosphere in the Common Era (4–6). out all but minor halogen emissions reaching the stratosphere. 11 Tree-ring proxy records and historical narratives point to- Including a minor fraction of the halogen inventory reaching the 12 ward a strong surface cooling in the Northern Hemisphere stratosphere captures the observed "muted" climate response 13 following the eruption, in the summer of 1258 (1, 7, 8). Con- but results in significant ozone depletion with implications for 14 temporary narrative sources suggest an unusually cloudy, rainy UV exposure and human health. 15 and cold summer in Europe in 1258 (1, 7). The climatic impact 16 of the eruption is suspected to have amplified famines and D.C.W., C.V. and A.T.A. conceived the study and A.S. contributed to the data interpretation. D.C.W., N.L.A., P.T.G., J.K., L.M., G.M. and S.D. performed model development. D.C.W. performed model 17 political turmoil in Europe and Japan, with the most severe and proxy-data analysis. D.C.W., C.V., A.T.A. and A.S. wrote the manuscript. 18 socio-economic consequences reported in England (7,9, 10). The authors declare no conflict of interest. 19 Given the magnitude of the eruption and the scale of the 1 20 societal impacts a number of previous climate modeling stud- To whom correspondence should be addressed. E-mail: [email protected] www.pnas.org/cgi/doi/10.1073/pnas.XXXXXXXXXX PNAS | September 1, 2020 | vol. XXX | no. XX | 1–9 Table 1. Summary of experiments performed to reconcile the climate 46 aerosols (which scatter back sunlight and cool the planet (18)) and ozone response to the Mt. Samalas eruption. Nsims refers to the 47 are formed from the oxidation of SO in the gas phase by the 2 number of ensemble members performed for each set of simulations. 48 hydroxyl radical (OH). Volcanic sulfate aerosols grow through In all simulations the same day of year and altitude is used to in- 49 microphysical processes of condensation and coagulation (19), ject the volatile gases from the eruption of Mt. Samalas. BOTH-SO2 50 with the size of the aerosols being important for their climate refers to the SO2 only experiments, which are averaged in further analysis. Percentages indicate the fraction of emissions compared 51 effects (20). There is an important self-limiting effect of sulfur to those estimated in (4) 52 oxidation in the stratosphere (17, 21). As the size of the SO2 53 injected into the stratosphere increases, the ability of the OH . Ensemble Nsims Stratospheric Injection 54 to react with SO2 decreases; slowing down the rate of aerosol SO2 / Tg(S) HCl / Tg HBr / Tg 55 production, causing sulfate to be produced over a longer time- HI-HAL (20%) 6 142.2 46.68 0.263 56 period and leading to a longer-lived forcing. In addition, the LO-HAL (1%) 6 94.8 2.33 0.013 57 reduction in OH can cause levels of ozone to increase in the BOTH-SO2 HI-SO2 (90%) 6 142.2 0.00 0.000 58 lower stratosphere (21) where it can act as a climate warming BOTH-SO2 LO-SO2 (60%) 6 94.8 0.00 0.000 59 agent. 60 One aspect that affects our understanding of the effects of 61 the Mt. Samalas eruption, and potentially other future erup- 62 tions, is in the role of co-emitted halogens. The impacts of As a prior study showed best model agreement for modeled 107 63 volcanic halogens on stratospheric ozone were first discussed surface temperature with reconstructed surface temperature 108 64 by Stolarski and Cicerone (22). When halogens enter the from tree-rings was with an eruption occurring between May 109 st 65 stratosphere they contribute to the catalytic destruction of and July (8), a 1 June eruption was selected for our sim- 110 66 ozone (23) and lead to commensurate impacts on the composi- ulations at the latitude and longitude corresponding to the 111 67 tion and chemistry of the troposphere. Tie and Brasseur (24), location of Mt. Samalas (8.5 °S, 116.3 °E). The gases listed in 112 68 showed that there is significant sensitivity in the response of Table1 were injected between 19 km and 34 km altitude (see 113 69 stratospheric ozone following eruptions the size of 1991 Mt. Methods). 114 70 Pinatubo eruption to the background chlorine levels. Kutterolf For each of the emissions scenarios six simulations were 115 71 et al. (25) provided renewed interest in the topic of volcanic performed (ensemble members) to investigate the role of inter- 116 72 halogens and several studies have recently been published us- nal variability.
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