Constraining the climatic impact of mystery volcanic eruptions

Overview

Large explosive volcanic eruptions are the most important natural drivers of climate variability and have led to major societal impacts in the past via the global cooling they exert. In an evolving climate, it is vital that we understand all drivers of climate change including those from natural sources. However, the climatic impact of eruptions that occurred before the satellite era is highly uncertain. This PhD project will improve estimates of the impacts of past eruptions using state-of-the-art climate modelling and proxy records.

Previous work has demonstrated that the climatic impact is dependent on many aspects of an eruption, including the amount of sulfur dioxide (SO2) emitted that goes on to form sulfate aerosol, the latitude of the volcano, the emission altitude, and the eruption season (e.g. Marshall et al., 2019). Sulfate produced from explosive volcanic eruptions is transported through the atmosphere and is eventually deposited to the Earth’s surface and on Greenland and Antarctica where it is incorporated into ice. Sulfate spikes in ice cores are an excellent record of past volcanism (e.g. Sigl et al., 2015) but many of the signals are from unidentified eruptions and could be attributable to a wide range of eruptions with different latitudes, SO2 emissions and emission altitudes (Marshall et al., 2021). This is problematic because eruptions with different properties have different climate impacts and consequently there is a large uncertainty associated with estimating the climatic impact of eruptions using only ice core sulfate deposition records.

Measurements of sulfur isotopes in ice cores can provide critical additional information. These measurements can be used to identify whether sulfate produced after an eruption was present in the stratosphere above the ozone layer due to exposure to UV radiation that produces a specific and time-evolving isotopic signature. These signals can be used to constrain the emission altitude and to make further inferences on whether the sulfate signal came from a tropical or an extratropical eruption (Burke et al., 2019) and consequently can be used to improve estimates of the climatic impact of past eruptions.

In this project, the candidate will explore the eruption properties and climatic impact of eruptions in the last 2500 years, focusing on climate modelling informed by sulfur isotope analysis, and, depending on the interest of the candidate, explore other records such as tree-ring records of volcanic cooling and trace-element compositions in speleothems. Constraining the climatic impact of past eruptions is crucial to improving simulations of historical climate to enable the detection and attribution of climate change and in quantifying the efficacy of volcanic forcing of climate.

Methodology

The project will involve running and analysing climate simulations using the UK Earth System Model (UKESM); collating and analysing proxy records of volcanism and eruption properties; and evaluating and constraining the simulations against these records. Although the project is predominantly model-based, the candidate will have the opportunity to learn how sulfur isotope measurements are made during a research visit to St Andrews. Specific tasks include:

1) Running UKESM simulations of eruptions with different properties using existing sulfur isotope data to inform the experiment design. The project will initially focus on simulating large unidentified eruptions such as those that occurred in 1452 or 1458 and explore the role of emission altitude and plume depth.

2) Developing the UKESM to simulate changes in sulfur isotopes that could be used to predict the isotopic signature following large eruptions to compare with measurements.

3) Analysing the output of the simulations to investigate the impact of eruptions on the atmosphere, the environment, and the climate. The model output will also provide opportunities to investigate possible societal impacts.

4) Constraining the properties and climatic impact of past eruptions by comparing model output with proxy records and combining insights from sulfur isotope data.

The project will also involve collaboration with Dr Anja Schmidt (University of Cambridge) enabling the candidate to benefit from expertise at the interface between Volcanology and climate modelling.

Project Timeline

Year 1

Conducting a literature review, exploring existing climate model data, and learning to run the UKESM. Research visits to the University of St. Andrews.

Year 2

Running UKESM for chosen eruptions and analysing output. Attendance at national conference (e.g. VMSG, RMetS)

Year 3

Evaluation of climate model simulations against proxy records and constraining properties and climatic impact of past eruptions. Attendance at international conference (e.g. EGU, AGU). Drafting publication.

Year 3.5

Thesis writing and paper submission

Training
& Skills

This project will ideally suit a candidate with a background in atmospheric and environmental sciences, physics, mathematics, or geology. Previous experience with computer programming (e.g. Python or MATLAB) is advantageous but not essential. The candidate will gain expertise in climate science, climate modelling, and volcanology, and gain a wide range of skills in data analysis and computer programming, scientific writing, and research presentations, relevant for employment in both academia and industry. The candidate will have the opportunity to attend the National Centre for Atmospheric Science (NCAS) introductory training courses in Atmospheric Science and Scientific Computing as well as model specific training courses in the Unified Model and the UK Chemistry and Aerosol Scheme that are core components of the UK Earth System Model. The candidate may also have the opportunity to attend a possible climate modelling summer school and will present their work at national and international conferences.

References & further reading

Burke, A., Moore, K. A., Sigl, M., Nita, D. C., McConnell, J. R., & Adkins, J. F. (2019). Stratospheric eruptions from tropical and extra-tropical volcanoes constrained using high-resolution sulfur isotopes in ice cores. Earth and planetary science letters, 521, 113-119.

Crick, L., Burke, A., Hutchison, W., Kohno, M., Moore, K. A., Savarino, J., … & Wolff, E. W. (2021). New insights into the ∼ 74 ka Toba eruption from sulfur isotopes of polar ice cores, Climate of the Past, 17, 2119–2137

Marshall, L., Johnson, J. S., Mann, G. W., Lee, L., Dhomse, S. S., Regayre, L., … & Schmidt, A. (2019). Exploring how eruption source parameters affect volcanic radiative forcing using statistical emulation. Journal of Geophysical Research: Atmospheres, 124(2), 964-985.

Marshall, L. R., Schmidt, A., Johnson, J. S., Mann, G. W., Lee, L. A., Rigby, R., & Carslaw, K. S. (2021). Unknown eruption source parameters cause large uncertainty in historical volcanic radiative forcing reconstructions. Journal of Geophysical Research: Atmospheres, 126, e2020JD033578.

Robock, A. (2000). Volcanic eruptions and climate. Reviews of geophysics, 38(2), 191-219.

Sigl, M., Winstrup, M., McConnell, J. R., Welten, K. C., Plunkett, G., Ludlow, F., … & Woodruff, T. E. (2015). Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature, 523(7562), 543-549.

Further Information

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