Volcanoes and Water Vapor Feedback in the Past and Implications for the Future

English Abstract:

The 1991 eruption of Mt. Pinatubo has long been used as a key forcing to assess the skill of GMCs in simulating feedbacks associated with tropospheric water vapor, radiation and dynamics. In particular, tropospheric water vapor decreases significantly after the eruption, magnifying the directly-induced surface cooling. In contrast, stratospheric water vapor increases in response to volcanic eruptions. Previous work has speculated that the climate response to historical volcanic eruptions, such as Krakatoa in 1883, may have in fact been mitigated by the direct addition of water vapor into the stratosphere.

We will describe in detail the water vapor response to volcanic eruptions over the last millennium to the present. We have tested two versions of the GISS-E2 model, one in which volcanic aerosol distribution and properties are prescribed, and another where we use prognostic model of aerosol microphysics (MATRIX) and model physics to produce a distribution consistent with direct emissions of volcanic output. Where possible, especially for the 1815 Tambora eruption (one of the largest and well constrained eruptions of the last millennium), we assess the skill of the model in simulating the appropriate sized temperature response to the volcanic forcing.

We find that in contrast to the prescribed-aerosol version, the stratospheric water vapor feedback in the MATRIX version of the model is much longer lasting. In addition, additional water vapor injection to the stratosphere in the MATRIX version does not attenuate the climate response, rather expedites the chemistry to convert the emissions to aerosols. We assess the impact that these contrasting responses could have on our ability to simulate future climate change – not only in response to volcanic forcing, but any strong global radiative perturbation, including greenhouse gases.