Description: The Los Chocoyos (14.6°N, 91.2°W) supereruption happened ∼75,000 years ago in Guatemala and was one of the largest eruptions of the past 100,000 years. It emitted enormous amounts of sulfur, chlorine, and bromine, with multi‐decadal consequences for the global climate and environment. Here, we simulate the impact of a Los Chocoyos‐like eruption on the quasi‐biennial oscillation (QBO), an oscillation of zonal winds in the tropical stratosphere, with a comprehensive aerosol chemistry Earth System Model. We find a ∼10‐year disruption of the QBO starting 4 months post eruption, with anomalous easterly winds lasting ∼5 years, followed by westerlies, before returning to QBO conditions with a slightly prolonged periodicity. Volcanic aerosol heating and ozone depletion cooling leads to the QBO disruption and anomalous wind regimes through radiative changes and wave‐mean flow interactions. Different model ensembles, volcanic forcing scenarios and results of a second model back up the robustness of our results.

Description: We petrologically estimated SO2 emissions from 36 detected Plinian volcanic eruptions occurring at the Central American Volcanic Arc (CAVA) during the past 200,000 years. Using this record and simple parameterized relationships collected from past studies we derive estimates of maximum volcanic aerosol optical depth (AOD) and radiative forcing (RF) for each eruption. For selected CAVA eruptions comprising different SO2 emission strengths, AOD and RF time series are derived in parallel from simulations with the global aerosol model MAECHAM5-HAM. The model shows a relationship between stratospheric SO2 injection and maximum global mean AOD that is linear for smaller volcanic eruptions (〈4 Mt SO2), and non-linear for larger ones ("4 Mt SO2), which is qualitatively and quantitatively consistent with the relationship used in the simple parameterized method. Potential climate impacts of the selected CAVA eruptions are estimated using an earth system model of intermediate complexity by RF time series derived (1) directly from the global aerosol model, and (2) from the simple parameterized method assuming a 12-month exponential decay of global AOD. We find that while the maximum AOD and RF values are consistent between the two methods, their temporal evolutions are significantly different. As a result, simulated maximum temperature anomalies and the duration of the temperature response depend on which RF time series is used, varying between 2.1 K and 3.1 K and ~ 60 and 90 years for the largest eruption of the CAVA data set. The presented results can be used to estimate the volcanic forcing and potential climate impacts from sulfur emissions, sulfate aerosol or AOD data for any tropical eruption that reached the stratosphere in the past but also in the future.

Description: We analyze simulated sea ice changes in eight different Earth System Models that have conducted experiment G1 of the Geoengineering Model Intercomparison Project (GeoMIP). The simulated response of balancing abrupt quadrupling of CO2 (abrupt4xCO2) with reduced shortwave radiation successfully moderates annually averaged Arctic temperature rise to about 1°C, with modest changes in seasonal sea ice cycle compared with the preindustrial control simulations (piControl). Changes in summer and autumn sea ice extent are spatially correlated with temperature patterns but much less in winter and spring seasons. However, there are changes of ±20% in sea ice concentration in all seasons, and these will induce changes in atmospheric circulation patterns. In summer and autumn, the models consistently simulate less sea ice relative to preindustrial simulations in the Beaufort, Chukchi, East Siberian, and Laptev Seas, and some models show increased sea ice in the Barents/Kara Seas region. Sea ice extent increases in the Greenland Sea, particularly in winter and spring and is to some extent associated with changed sea ice drift. Decreased sea ice cover in winter and spring in the Barents Sea is associated with increased cyclonic activity entering this area under G1. In comparison, the abrupt4xCO2 experiment shows almost total sea ice loss in September and strong correlation with regional temperatures in all seasons consistent with open ocean conditions. The tropospheric circulation displays a Pacific North America pattern-like anomaly with negative phase in G1-piControl and positive phase under abrupt4xCO2-piControl.