Volcanic eruptions inject sulfur gases into the atmosphere which form tiny sulfate aerosol particles that reflect light from the sun, resulting in a reduction of the Earth’s surface temperature. The eruption of Tambora in 1815 was followed by the “Year Without a Summer”, during which starvation affected parts of North America and Europe. Global cooling related to explosive eruptions contributed to a slight slow-down in the rate of anthropogenic global warming over 2000-2014. A major challenge for predicting future climate lies in our inability to predict volcanic eruptions more than days in advance. Consequently, climate model projections assume that volcanic “forcing” on climate, i.e. the impact of volcanic gases on the radiative energy received by Earth, is constant. However, volcanic forcing can vary by a factor 3-4 from one century to another. This large uncertainty is currently ignored. Furthermore, the rise of a volcanic column, the life cycle and transport of sulfate aerosols particles, and the climatic impacts of these aerosols are all sensitive to climate. The assumption of a constant volcanic forcing in a warming Earth is thus flawed. Accordingly, the overarching objective of this project was to develop new strategies to represent volcanoes in climate models. Specifically, the project produced new experiments with the state-of-the-art UK climate model to:
1 – Determine how the climate response to future eruptions will be affected by interactions between volcanoes and anthropogenic global warming.
2 – Determine how a statistically realistic distribution of volcanic eruptions would affect future climate change projections, and the uncertainties on these projections.
This research aims to feed Assessment Reports of the Intergovernmental Panel on Climate Change and, in turn, help global and local societies to face the challenges posed by global climate change.
To reach the first objective, models for the rise of volcanic columns are required to investigate how global warming may affect the distribution of volcanic gases in the atmosphere. These models are critical for managing volcanic crises as they provide predictions for the dispersion and fallout of ash and the occurrence of “pyroclastic flows” (devastating avalanches of burning volcanic rocks). Even relatively minor eruptions can have profound consequences in our globalized world. The ash clouds of the 2010 Eyjafjallajökull eruption disrupted transatlantic flights at a cost of billions of dollars. The evaluation of models of volcanic column is notoriously challenging owing to difficulties to gather independent observations of model inputs (e.g. the flux of ash and gas coming out from a crater) and outputs (e.g. the height of a volcanic column). In turn, this hinders the reliability of model predictions and volcanic risk assessment. Accordingly, the third and fourth objectives of this project were:
3 – Deliver a new, state-of-the-art database of independently estimated eruption parameters that will become a reference tool for evaluating volcanic plume models.
4 – Apply this database to conduct an observationally-constrained plume model comparison, and use enhanced models to improve the assessment of climate-volcano feedbacks related to plume rise as well as risks related to ash dispersion.
The new database is designed to become a flagship product of the international volcanology community. It will contribute to improve ash dispersion forecast and, in turn, the warnings issued by the Volcanic Ash Advisory Centers which are in charge of communicating with aviation authorities during volcanic crises.
