Comparing the Responses of Stratospheric Dynamics to Volcanic Eruptions and Sulfate Climate Engineering in CMIP5 and Geomip Simulations

Abstract:

The suggestion of injecting sulfur into the stratosphere to cool the climate is motivated by the response of the climate system to large volcanic eruptions. But can we expect that the effects observed after eruptions accurately describe the effects of sulfate climate engineering? Here we discuss the response of stratospheric dynamics to both types of forcing as simulated in state-of-the-art climate models.

The cooling observed after volcanic eruptions is not homogeneous in space and time. An anomalous warming has been observed after several big tropical eruptions during boreal winter in northern Europe and Asia. In general, this warming is attributed to a strengthening of the stratospheric polar night jet, related to the stratospheric effects of volcanic aerosol, and a subsequent downward propagation of this dynamical signal. Here we use the Geoengineering Intercomparison Model Project (GeoMIP) G3 and G4 simulations where sulfur is injected to reduce warming during the 21^st century to study the potential response of stratospheric dynamics to this type of climate engineering and compare it with the response to volcanic eruptions simulated by the same models in the CMIP5 historical simulations. Unfortunately, in general the CMIP5 models do not reproduce the strengthening of the polar night jet well. Potential reasons for this will be discussed. Furthermore we show that due to the different time scales involved in volcanic eruptions in comparison to assumed climate engineering the dynamical responses may differ.