Abrupt climate and sea level change

This PhD project will use numerical modelling to examine the causes and consequences of rapid climate and sea level change. Case studies from past deglaciations will be utilised to reach a new level of understanding for the link between ice sheet melting and sea level rise, rapid cooling, abrupt warming and the complete reorganisation of Atlantic Ocean circulation.

Iceberg. Credit: HC Ng, 2018

At the Last Glacial Maximum (21,000 years ago), vast ice sheets stretched across much of the Northern Hemisphere. As climate warmed and the ice began melting, an intriguing and catastrophic chain of events was triggered: Largescale ocean circulation slowed, climate cooled, armadas of icebergs were released, sea level rose at an unprecedented rate, ocean circulation rapidly strengthened, temperatures suddenly increased by several degrees in a few decades…and then it all happened again just a few centuries later. Although well documented individually (known as: Heinrich Stadial 1, Heinrich Event 1, Meltwater Pulse 1a, the Bølling Warming and the Younger Dryas), we still do not know precisely how and even if these events are linked. Perhaps even more intriguingly, we know that many of the events have occurred repeatedly in Earth’s past, suggesting there are consistent but currently unknown mechanisms in the Earth System for triggering abrupt climate change.

The scientific community remains divided on the cause of the events, but there is consensus that the mechanisms are important to understand in order to predict when they will occur. As atmospheric carbon dioxide rises in the coming years, and the Greenland and Antarctic ice sheets continue to melt, could these catastrophic events be triggered again?

This exciting project will tackle this challenge directly, testing ice-ocean-atmosphere interactions that take place during deglaciations in order to produce seminal new knowledge on our climate. You will be at the heart of two international projects producing new model simulations and observational records of past abrupt climate change: The Paleoclimate Model Intercomparison Project (PMIP) Deglaciations Working Group and The International Union for Quaternary Research Focus Group on Deglaciations, both coordinated by Dr. Ruza Ivanovic. Thus, you will be granted access to the latest results and thinking from world-leading scientists, and, positioned at the forefront of international research into past warming climates, you will have the opportunity to feed into the global research agenda.

Please contact the lead supervisor (r.ivanovic@leeds.ac.uk) for more information and before applying.

Project Aim
You will run and analyse complex numerical earth system models to examine the interplay between climate, ice sheets, icebergs and ocean circulation. You will compare the results from these simulations to observational records to evaluate model performance, verify/refute existing explanations for the events, and build and test new hypotheses. The overall aim is to establish the mechanisms that link ice, atmosphere and ocean in the Earth System, then explore the possibility that such rapid and catastrophic events as we know have occurred in the past will occur again in the future.

Examples of research questions to be addressed
It is expected that the project will evolve in line with the best research on the topic. You will be fully supported to follow you interests and make the project your own. Here is an example of the direction the PhD could take, including a selection of possible research questions to answer:

Chapter/paper 1:
Compare simulations of the last deglaciation with observational records

  • What are the timings, rate of change and amplitude of the abrupt events?
  • How well do the models capture past rapid climate changes?
  • What are the inherent uncertainties in this model-observation comparison?
  • How can PMIP and INQUA activities reduce or eliminate these uncertainties?

Chapter/paper 2:
Interrogate mechanisms of abrupt climate change triggered in the atmosphere

  • Were the events initiated by crossing a critical threshold in ice sheet geometry1,2 or atmospheric carbon dioxide3,4?
  • What are the atmospheric processes that propagate, amplify or counteract the events?
  • What are the feedbacks from ice sheet evolution and interactions with the ocean?
  • What is the scope for such events happening in the future?

Chapter/paper 3:
Interrogate mechanisms of abrupt climate change triggered in the ocean

  • What was the role of ice sheet meltwater in causing5–7 or counteracting8 past rapid climate change?
  • Are these results sensitive to the initial ocean state?
  • Were ocean-driven abrupt changes the result of an inherently unstable earth system that can suddenly flip between different climate regimes9,10?
  • Which of the identified mechanisms may be triggered again in the future?

International Network
The candidate will have the opportunity to be a part of the following international research networks, working with scientists from around the world to generate and gain hot-off-the-press access to cutting-edge knowledge on rapid climate and sea level change:

Potential for high-impact research
This exciting and novel work employs recent, groundbreaking developments in our knowledge of climate-ice-ocean interactions and the ability to simulate them. The student will develop a highly sought-after, multidisciplinary skill-set, contributing towards the development of an interdisciplinary field of research that is at the forefront of climate science. By the nature of this work, and due to its timeliness, there is strong potential for the PhD candidate to influence the direction of international research being carried out on this theme, and to thus establish a world-renowned reputation for innovative science.

Training, support and research opportunities
This project affords many exciting opportunities for skills and research development, in particular:

Full-support for all technical and scientific aspects of the project, including the model development work, will be provided in-house (Leeds) and by external collaborators. With this training, the student will be well equipped to pursue their own research interests.

Entry requirements
A good first degree (1 or high 2i), Masters degree or equivalent in a physical or mathematical discipline; such as Physics, Mathematics, Oceanography, Meteorology, Climate Sciences, Earth/Environmental/Geographical Sciences, Chemistry, Engineering or Computer Sciences. Some experience of computer programming is highly desirable e.g. in Fortran, C++, Python, MATLAB, IDL or R etc…

Further information

Specific background literature cited in the project description:

  1. Zhang, X., Lohmann, G., Knorr, G. & Purcell, C. Abrupt glacial climate shifts controlled by ice sheet changes. Nature 512, 290–294 (2014).
  2. Gregoire, L. J., Payne, A. J. & Valdes, P. J. Deglacial rapid sea level rises caused by ice-sheet saddle collapses. Nature 487, 219–222 (2012).
  3. Obase, T. & Abe‐Ouchi, A. Abrupt Bølling-Allerød Warming Simulated under Gradual Forcing of the Last Deglaciation. Geophysical Research Letters 46, 11397–11405 (2019).
  4. Zhang, X., Knorr, G., Lohmann, G. & Barker, S. Abrupt North Atlantic circulation changes in response to gradual CO2 forcing in a glacial climate state. Nature Geosci 10, 518–523 (2017).
  5. Liu, Z. et al. Transient Simulation of Last Deglaciation with a New Mechanism for Bølling-Allerød Warming. Science 325, 310–314 (2009).
  6. Menviel, L., Timmermann, A., Timm, O. E. & Mouchet, A. Deconstructing the Last Glacial termination: the role of millennial and orbital-scale forcings. Quaternary Science Reviews 30, 1155–1172 (2011).
  7. Ivanovic, R. F. et al. Acceleration of northern ice sheet melt induces AMOC slowdown and northern cooling in simulations of the early last deglaciation. Paleoceanography and Paleoclimatology 33, 807–824 (2018).
  8. Ivanovic, R. F., Gregoire, L. J., Wickert, A. D., Valdes, P. J. & Burke, A. Collapse of the North American ice saddle 14,500 years ago caused widespread cooling and reduced ocean overturning circulation. Geophys. Res. Lett. 44, 383–392 (2017).
  9. Klockmann, M., Mikolajewicz, U. & Marotzke, J. Two AMOC states in response to decreasing greenhouse gas concentrations in the coupled climate model MPI-ESM. J. Climate (2018).
  10. Peltier, W. R. & Vettoretti, G. Dansgaard-Oeschger oscillations predicted in a comprehensive model of glacial climate: A “kicked” salt oscillator in the Atlantic. Geophys. Res. Lett. 41, 2014GL061413 (2014).

Broader background literature:

  1. Clark, P.U et al. Global climate evolution during the last deglaciation. PNAS 109, E1134–E1142 (2012)
  2. Ivanovic, R.F. et al.Transient climate simulations of the deglaciation 21–9 thousand years before present (version 1) – PMIP4 Core experiment design and boundary conditions. Geoscientific Model Development 9, 2563–2587 (2016)
  3. Menviel, L. et al. The penultimate deglaciation: protocol for Paleoclimate Modelling Intercomparison Project (PMIP) phase 4 transient numerical simulations between 140 and 127 ka, version 1.0. Geoscientific Model Development 12, 3649–3685 (2019).

YouTube videos: Reconstructing climate history and drivers of ocean circulation