Search for a project

Atmospheric forcing of decadal climate variability

Dr Amanda Maycock (SEE), Prof Piers Forster (SEE), Dr Doug Smith (Met Office)

Project partner(s): Met Office (CASE)

Contact email: a.c.maycock@leeds.ac.uk

Overview

This PhD project offers the exciting opportunity to perform cutting edge climate research alongside leading scientists at the University of Leeds and the UK Met Office. The focus of the PhD is on the important topic of decadal climate prediction, which has been identified as a Grand Challenge for climate science by the World Climate Research Programme. You will undertake visits to the Met Office and learn how to perform and analyse decadal climate predictions using state-of-the-art computer modelling and data analysis tools. The project will allow you to connect with a large network of UK scientists involved in the NERC-funded SMURPHS project (Securing Multidisciplinary Understanding and Prediction of Hiatus and Surge Events) and with scientists around the world engaged with the Decadal Climate Prediction Project (DCPP) [1].

Introduction

A deeper understanding of the factors that affect Earth's climate is vital for the development of informed policies for mitigating and adapting to climate change. There is growing recognition of the importance of predicting climate on decadal timescales, as most planning decisions are made in the near-term rather than for many decades in the future. Observed changes in climate arise from both external forcing, such as greenhouse gases, and chaotic fluctuations generated by the climate system itself (climate variability). On decadal timescales, climate variability can mask the climate signals associated with forced changes from human activities [2]. It is therefore important to understand the mechanisms that determine climate variability on decadal timescales and their associated impacts in past and future climates. This project will seek to address this need by building new understanding of the role of atmospheric processes in driving decadal climate variability.

A pertinent recent example is the slowing in the rate of global warming over 1998-2012 despite continued emissions of greenhouse gases into the atmosphere. This slowdown has been linked to a tendency towards a negative phase of the Pacific Decadal Oscillation (PDO) [3], a major mode of climate variability that fluctuates from one decade to the next. The recent trend towards a negative PDO phase was in part driven by a strengthening of tropical wind patterns [4], which in turn has been shown to be driven by changes in the emission of small particles (aerosols) into the atmosphere from human activity in East Asia [5]. This offers the tantalising prospect that there is a connection between internal modes of climate variability and the response to external forcings like aerosols. This PhD will explore this emerging scientific topic.

Figure 1: Patterns of near-surface temperature change (°C per decade) over 1998-2012. (a) Observed change; (b) climate model simulated trend due to aerosols; (c) climate model simulated trend due to greenhouse gases. The observed cooling trend in the tropical Pacific (red box) is only captured when the climate models are forced with anthropogenic aerosol changes. This local response occurs through changes in atmospheric circulation patterns. Adapted from [5].

Objectives

The project will address the following key questions:

  1. What are the mechanisms through which atmospheric circulation patterns drive decadal variations in ocean circulation?
  2. What are the roles of different external forcing agents (e.g. greenhouse gases, aerosols) in driving changes in the patterns of atmospheric circulation in past and future climates?
  3. Can the drivers identified in 2) help us to interpret decadal variations in the Pacific Ocean over the recent past?

These research questions are synergistic with the ongoing SMURPHS (Securing Multidisciplinary Understanding and Prediction of Hiatus and Surge events) NERC-funded project led by the University of Leeds, which the supervisory team are closely involved with. SMURPHS will provide the student with a strong research network to engage with on the topic of decadal climate prediction.

Research tools

The research questions outlined above will be addressed using observational datasets and the Met Office’s state-of-the-art coupled atmosphere-ocean Decadal Prediction System (DePreSys3).

Depending on the interests of the successful candidate, the main research objectives could include:

  1. Perform statistical analyses of observational datasets and long simulations from climate models to identify the patterns of atmospheric circulation that precede changes in major modes of decadal climate variability, such as the PDO.
  2. Perform with the assistance of the Met Office decadal climate prediction experiments using DePreSys3 [6]. Experiments will be run for select case studies corresponding to periods of relatively weak surface warming and relatively strong surface warming. The unique feature of the experiments is that the atmosphere will be “nudged” towards observations to reproduce closely the observed history.
  3. Perform further experiments with DePreSys3 to identify how different anthropogenic forcings (e.g. greenhouse gases, aerosols) force modes of decadal climate variability and attribute their role in climate fluctuations over the recent past.

Structuring the project in this way provides a progression in developing skills from analysing observation datasets and existing model experiments to performing new model runs. There will be support from within the Met Office and from within the SMURPHS project to assist in performing the simulations and analysis. Prior experience in scientific programming is not required, but a desire to learn new programming and modelling techniques is essential.

Key outputs and potential for high impact

The alignment of the PhD project with the NERC-funded SMURPHS project and with the research activities within the Monthly-to-decadal Prediction Group in the Met Office Hadley Centre will ensure that the project delivers wider impact of strategic relevance to the Met Office. There have been a series of recent high profile papers published from the Met Office using new results from the recently developed DePreSys3 system. The student will undertake regular visits to the Met Office during the project.

There is international recognition of the growing need for accurate and skilful near-term climate predictions to inform the public, policy makers and stakeholders. This project will seek to address this need by building new understanding of how forced and unforced mechanisms drive decadal climate variability. It is expected that the project will lead to several high quality publications in the peer-reviewed scientific literature that may be relevant for upcoming Intergovernmental Panel on Climate Change Reports and World Climate Research Programme activities.

Training

The School of Earth and Environment (SEE) was ranked 2nd in the UK for Research Power in “Earth and Environmental Sciences” in the 2014 UK Research Excellence Framework (REF) Assessment. The student will be based within the Physical Climate Change research group in the Institute for Climate and Atmospheric Science (ICAS) in SEE, which consists of 7 academic staff and 14 PhDs and postdoctoral researchers who meet regularly providing a supportive forum to discuss research and receive feedback on your work.

Specific skills that will be developed during the project include:

(1) Techniques to handle the large data sets produced by models.

(2) Application of statistical analysis methods to ensemble decadal predictions.

(3) Understanding of sources of uncertainty in predictions.

(4) Use of observational datasets to evaluate model simulations.

(5) Working with people from a range of backgrounds.

(6) Effective communication through presentations at conferences, informal talks at project meetings, and writing peer-reviewed journal articles.

The student will be expected to undertake regular visits to the CASE supervisor to ensure effective collaboration and interactions. The student will receive assistance from the CASE supervisor and other Hadley Centre scientists in learning how to perform DePreSys3 experiments on high performance computing facilities. The wider SMURPHS project involves more than 20 scientists from 9 Universities and Research Centres around the UK. The SMURPHS project will therefore provide significant further opportunities for scientific training and networking, including attendance at SMURPHS project and science meetings.

There will be numerous opportunities present your research at national and international conferences and meetings, as well as to attend summer schools and other training workshops. In addition, an active internal and external seminar series within ICAS will provide a broad background in research topics across atmospheric and climate science. 

Leeds hosts a NERC Doctoral Training Partnership (DTP), which recruits a total of 28 students per year across 6 departments. This fosters a strong research student cohort in which students feel part of a strong and lively community and take advantage of the many research, training and social opportunities that are available. The University of Leeds also offers a tailored programme of dedicated training and development courses for postgraduate researchers, see: http://www.emeskillstraining.leeds.ac.uk/.

The University of Leeds is a member of the Met Office Academic Partnership, which gives students access to Met Office models, datasets and seminar series. The Priestley International Centre for Climate has been established at the University of Leeds to promote interdisciplinary research in Climate Science across several Departments and offers graduate-level lectures on topics in climate science, modelling working groups and training in communication to policy makers and the public.

Further information

https://www.smurphs.leeds.ac.uk

https://www.wcrp-climate.org/dcp-overview

https://www.wcrp-climate.org/grand-challenges/gc-near-term-climate-prediction

https://www.metoffice.gov.uk/research/climate/seasonal-to-decadal

Further reading/references

[1] Boer, G. J., Smith, D. M., Cassou, C., Doblas-Reyes, F., Danabasoglu, G., Kirtman, B., Kushnir, Y., Kimoto, M., Meehl, G. A., Msadek, R., Mueller, W. A., Taylor, K. E., Zwiers, F., Rixen, M., Ruprich-Robert, Y., and Eade, R.: The Decadal Climate Prediction Project (DCPP) contribution to CMIP6, Geosci. Model Dev., 9, 3751-3777, https://doi.org/10.5194/gmd-9-3751-2016, 2016.

[2] Deser, C., R. Knutti,       S. Solomon, and A. S. Phillips (2012) Communication of the role of natural variability in future North American climate, Nature Climate Change, 2, 775–779, doi:10.1038/nclimate1562.

[3] Kosaka, Y. and S.-P. Xie (2013) Recent global-warming hiatus tied to equatorial Pacific surface cooling, Nature, 501, 403–407, doi:10.1038/nature12534.

[4] England, M. H., S. McGregor, P. Spence, G. A. Meehl, A. Timmermann, W. Cai, A. Sen Gupta, M. J. McPhaden, A. Purich and A. Santoso (2014) Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus, Nature Climate Change, 4, 222–227, doi:10.1038/nclimate2106.

[5] Smith, D. M., B. B. B. Booth, N. J. Dunstone, R. Eade, L. Hermanson, G. S. Jones, A. A. Scaife, K. L. Sheen and V. Thompson (2016) Role of volcanic and anthropogenic aerosols in the recent global surface warming slowdown, Nature Climate Change, 6, 936–940, doi:10.1038/nclimate3058

[6] Smith, D. M., S. Cusack, A. W. Colman, C. K. Folland, G. R. Harris and J. M. Murphy, 2007, Improved surface temperature prediction for the coming decade from a global climate model, Science, 317, 796-799, doi:10.1126/science.1139540

Related undergraduate subjects:

  • Applied mathematics
  • Atmospheric science
  • Computer science
  • Mathematics
  • Meteorology
  • Natural sciences
  • Oceanography
  • Physical science
  • Physics