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Aerosol pollution impacts on climate projections

Prof Ken Carslaw (SEE), Dr Lindsay Lee (SEE), Dr Ben Booth (Met Office)

Project partner(s): Met Office (CASE)

Contact email: k.s.carslaw@leeds.ac.uk

This is a fully funded project and is not part of the DTP competition, applications should be made directly to the hosting department, see http://www.see.leeds.ac.uk/admissions-and-study/research-degrees/how-to-apply/ for more information.

This is a 4-year fully funded NERC Industrial CASE award and eligibility will normally be for UK or some EU candidates who meet the 3 years residency requirement that immediately precedes the start of the PhD study.  The award will include tuition fees (£4,250 for 2016/17), tax-free stipend (£14,296 for 2016/17), and research training and support grant.

The Met Office is tasked with providing up to date information on how climate change will impact the UK.  A key part of this task is understanding and exploring current uncertainties in climate processes and what they imply for projected future climate. This PhD project will explore and quantify the effect of large uncertainties related to how aerosol pollution affects climate. 

The Intergovernmental Panel on Climate Change estimates that changes in aerosols over the industrial period have caused a radiative forcing of between -0.1 to -2 W/m2. This large cooling effect is comparable in magnitude to the warming effect of greenhouse gases, so aerosol pollution is a major driver of climate change. The uncertainty surrounding aerosols influences future climate projections in two ways.  First, it influences how well we understand simulated historical climate, which directly affects our confidence in future projections. Second, there are likely to be rapid reductions in aerosol pollution over the next 2-4 decades, which will strongly influence how the warming will accelerate.

The project will use large ensembles of model simulations combined with extensive observational data from ground sites, ships, aircraft and satellites to narrow the uncertainty in model simulations and climate projections.

This is a collaborative project with the Met Office “Understanding Climate Change” department, co-supervised by Dr Ben Booth. The project would suit students who are interested in pursuing a career in climate sciences, as well as maths and computing students who want to apply their skills to challenging new problems.

Project details

The main research question are:

  1. What are the main causes of uncertainty in aerosol effects on regional and global climate?
  2. How much can the uncertainty realistically be reduced by constraining aerosol and cloud model processes using observations?
  3. What effect does narrowing the range of aerosol forcing considered plausible imply for future projections?  Are some of the projected changes more plausible than others?

The research is related to the next update of the UK Climate Projections in 2018 (UK18). The Met Office will release climate data that will inform the UK's 3rd national Climate Change Risk Assessment. The project will provide a wider context on the plausibility of the range of aerosol processes in the UK18 projections, and identify model-observed comparisons that can be used in updates to projections beyond 2018.

The student will be aiming to understand what their model-observation comparisons imply about the range of plausible aerosol forcings simulated by the climate models.  The research will provide a context for end users of these projections to better inform how they use these datasets. For example, are projected strong changes in near-term temperature response plausible based on what we know about aerosol forcings?

From the Met Office's perspective, there is a longer-term benefit for climate projection systems.  Insights on the value of particular model-observation comparisons will be incorporated into the development of future climate projections, beyond 2018.  This will place the uncertainty estimates in these future projections on a more robust footing.

The student will initially use an existing large ensemble of climate model simulations exploring uncertainties in aerosols alongside other climate components.  These will be used along with advanced statistical analysis techniques to quantify the model spread in aerosol forcing. Then extensive aerosol and cloud observations will be used to constrain the uncertain processes to define a narrower “observationally plausible” forcing range. We expect the student will need to design their own model ensemble to enable optimum comparison with additional aerosol and cloud satellite observations.

The research is at the frontier of how statistical methodologies are used to design and analyse model simulations.

University and Met Office supervision

The new student will be embedded within a highly diverse and successful aerosol modelling group, with research interests spanning global aerosols and climate, volcanic impacts, ice nucleation, dust, natural aerosol processes, aerosol-cloud interaction and uncertainty quantification. The wider atmospheric composition group of Spracklen, Rap, Schmidt, Chipperfield and Mann of several postdocs and students is a rich environment for a CASE PhD student.

The lead supervisor, Prof Ken Carslaw, has been investigator on over 25 NERC projects and 10 EU projects. He has supervised over 20 PhD students (several in collaboration with the Met Office) and 20 postdocs. Ken’s group developed the Global Model of Aerosol Processes (GLOMAP), which will be used in this PhD project. GLOMAP is now an integral part of the UK climate model.

The co-supervisor, Dr Lindsay Lee, is an independent Leverhulme Fellow. She is a trained statistician using advanced statistical methods to better understand Earth science models and the visualisation of statistical results for scientific interpretation. She is the only academic statistician to be embedded within an environment department in the UK.

The Met Office supervisor, Dr Ben Booth, has 12 years postdoctoral research experience as part of the core group developing UK Climate Projections where his main remit is to quantify (and reduce) the impact of uncertainties in the earth system components of the climate system. Ben has contributed to a number of important advances that link aerosol emissions to climate impacts.  These include linking changes in past aerosol emissions to tropical storms, ITCZ shifts and Sahel drought.

Recent Met Office CASE students in the Leeds aerosol group have been very successful: Matthew Woodhouse is a member of staff at CSIRO in Australia; Jo Browse is a lecturer in Geography at Exeter University; Steven Turnock is a member of staff at the Met Office; Douglas Hamilton is a postdoc at Cornell University in the US and Leighton Regayre is a postdoc at Leeds. All have won PhD publication prizes at Leeds.

Research environment

The student will join the vibrant Atmospheric Composition research group of 6 Academic Staff and one of 50 PhD students across the Institute for Climate and Atmospheric Science (ICAS) covering climate, dynamics, impacts, with extensive programmes in observations, modelling and lab studies.  Wider interdisciplinary experience is guaranteed through our new cross-campus Priestley Centre (climate.leeds.ac.uk). Peer exchange and learning occurs through frequent institute and group seminars, discussion meetings and paper review groups.

The Met Office's Hadley Centre for Climate Research is a world class centre employing more than 150 scientist working across observations, climate processes, climate model development and assessment. This environment offers opportunities for the student to engage with a cross section of the current climate research (via regular seminar series and peer group meetings).  The student will sit within the Understanding Climate Change (30+ people) and the Seamless Ensemble Prediction (7 people) groups.  The members of these two groups range from early year to internationally recognised scientists.  Regular group meetings provide a forum to present and share work and to gain insight and feedback from your peers.

The collaboration between Leeds and the Met Office goes back over nearly 20 years and is now formalised as the Met Office Academic Partnership (MOAP: http://www.metoffice.gov.uk/research/partnership). There is therefore an active group of Met Office-facing scientists at Leeds.

Training opportunities

The PhD provides training in running and analysing state of the art models. You will also have the opportunity to acquire valuable transferable skills related to designing model experiments, model emulation, expert elicitation, model calibration, visualisation and analysis of observational data, etc. The institute’s new purpose-designed research computing centre (CEMAC.leeds.ac.uk) provides specialised training in code management, version control, code standards, visualisation, etc. You will receive mentoring on the use of Met Office systems, visualisation tools and analysis from the CASE supervisor. The Met Office will provide training in how to write model code to operational standards. In short, you will be very employable.

Student profile

The PhD is well suited to students with a degree in physical or chemical sciences. It would also be suitable for students with a maths, statistics or computing-based degree who are keen to apply their knowledge in an exciting field of research. Depending on background, there are opportunities to focus more on the climate science or on the challenges of applying advanced statistical techniques to extract the maximum information from model simulations and observations.

Further information

We strongly encourage students to discuss the project with the lead supervisor. We would be happy to answer questions by email, on the phone or in person.

Funding

This project is a fully funded studentship with CASE enhancement. The CASE funding is already secured.

Related publications

Carslaw KS; Lee LA; Reddington CL; Pringle KJ; Rap A; Forster PM; Mann GW; Spracklen DV; Woodhouse MT; Regayre LA; Pierce JR (2013) Large contribution of natural aerosols to uncertainty in indirect forcing, NATURE, 503, pp.67-+. doi: 10.1038/nature12674.

Lee LA; Reddington CL; Carslaw KS (2016) On the relationship between aerosol model uncertainty and radiative forcing uncertainty, Proceedings of the National Academy of Sciences, 113, pp.5820-5827. doi: 10.1073/pnas.1507050113

Regayre LA; Pringle KJ; Lee LA; Rap A; Browse J; Mann GW; Reddington CL; Carslaw KS; Booth BBB; Woodhouse MT (2015) The Climatic Importance of Uncertainties in Regional Aerosol-Cloud Radiative Forcings over Recent Decades, JOURNAL OF CLIMATE, 28, pp.6589-6607. doi: 10.1175/JCLI-D-15-0127.1

Regayre LA; Pringle KJ; Booth BBB; Lee LA; Mann GW; Browse J; Woodhouse MT; Rap A; Reddington CL; Carslaw KS (2014) Uncertainty in the magnitude of aerosol-cloud radiative forcing over recent decades, Geophysical Research Letters, 41, pp.9040-9049. doi: 10.1002/2014GL062029

Lee LA; Pringle KJ; Reddington CL; Mann GW; Stier P; Spracklen DV; Pierce JR; Carslaw KS (2013) The magnitude and causes of uncertainty in global model simulations of cloud condensation nuclei, Atmospheric Chemistry and Physics, 13, pp.8879-8914. doi: 10.5194/acp-13-8879-2013

Hamilton DS; Lee LA; Pringle KJ; Reddington CL; Spracklen DV; Carslaw KS (2014) Occurrence of pristine aerosol environments on a polluted planet, Proceedings of the National Academy of Sciences of the United States of America, 111, pp.18466-18471. doi: 10.1073/pnas.1415440111