Nonlinear precipitation and temperature response to large low-latitude eruptions spanning the last two millennia

We ask whether the temperature and precipitation response to large, low-latitude volcanic eruptions is a linear function of the eruption magnitude, as measured by the mass (in Teragrams) of sulfur injected in the lower stratosphere (TgS).  Consider the last 2,000 years, magnitudes of climatically interesting eruptions range from roughly 10 TgS from the 1991 Pinatubo and the 1883 Krakatau eruptions, to nearly 30 TgS for the 1815 eruption, to almost 60 TgS for the largest event, the 1257 Samalas eruption.  To span this entire range, we simulate eruptions of 5, 10, 20, 40, 80 and 160 TgS, using a state-of-the art climate model with a well-resolved stratosphere.  For each eruption magnitude we run a 20-member ensemble of 10-year-long simulations.

We confirm earlier studies, and find that the response is linear up to 20 TgS.  However, for eruptions of 40 TgS and above, our analysis reveals a clear nonlinear relationship between eruption magnitude and climate response.  We also find important differences between the responses in temperature and precipitation: while the temperature response saturates after 40 TgS, the precipitation response continues to increase in magnitude albeit at a reduced rate.  Furthermore, we find that the controlling mechanisms driving the precipitation response are different for the weakest and strongest events.  For small eruptions the precipitation anomalies are primarily driven by the cooling surface temperatures (slow response), while for the largest eruptions they are dominated by the absorption of longwave radiation by the volcanic aerosols which warms the lower stratosphere (fast response).