CCSM run aschmidt, Atmosphere Climatology, Unspecified Time Frequency, version 1

We calculate the climatic effects of explosive volcanic eruptions between 1979 and 2015 using a more complex climate model simulation than has been used previously. This includes many of the chemical and physical processes that lead to the formation of volcanic aerosol. Volcanic aerosols are tiny airborne particles that are important for Earth's climate because they reflect sunlight and trap thermal infrared radiative energy. In line with previous studies, we find that the most powerful eruptions between 1979 and 2015 had a substantial cooling effect. However, we calculate that their effect on climate is about 20% weaker than previous estimates used by the Intergovernmental Panel on Climate Change (IPCC). In our model simulation this is mainly a result of the volcanic aerosol particles affecting ice clouds, making these clouds less transparent. We also find that it is very rare to have a period with relatively few notable explosive eruptions as was the case during 1996–2002. Furthermore, eruptions of small-to-moderate size occur frequently and decrease the transparency of the stratosphere by as much as all nonvolcanic sources of aerosol particles combined. These small-sized volcanic eruptions therefore cause a small but noticeable surface cooling and so should be included in climate model simulations, which is rarely done.