Climate effects of northern hemisphere volcanic eruptions in an Earth System Model

We study climate effects of mid- and high-latitude volcanic eruptions seen in an ensemble of six 1200-year simulations with the COSMOS Earth System Model. 18 eruptions are studied, of which 7 happen in January, 8 in July and 3 in September. The average aerosol optical depth (AOD) over latitudes north of 30° N reached after the eruptions ranges from 0.1030 to 0.2941. The largest maximum monthly effects on clear-sky shortwave radiation occur for the January eruptions (in the following summer), but for the averaged quantity over the 21 months following the eruptions, the summer eruptions cause a larger effect. Largest zonal average radiative forcings are 5–6 W m‐2 (cooling). Average maximum perturbation of northern hemisphere monthly mean temperature is − 0.19 K and is on average − 0.095 K during the 21 months following an eruption. The maximum decrease in northern hemisphere temperature is not that sensitive to the time of the eruption but depends more on the size of the eruption. July and September eruptions, however, cause a larger average effect on northern hemisphere mean temperature for the 21 months following the eruptions. The precipitation anomaly is on average − 0.0058 mm/day during the 21 months following an eruption, and though the signal is weak compared to climate variability, our large sample allows us to assign 90% significance to the decrease in precipitation. Effects on atmospheric carbon dioxide and the resulting feedbacks are small.