Aerosol interactions and feedbacks in the Earth system
Ken Carslaw, Dom Spracklen + CASE partner Gerd Folberth (Met Office, Exeter)
Enquires: Prof Carslaw, lecksc(at)ds.leeds.ac.uk
Background
Atmospheric particulates (aerosols) are a major cause of climate change. Aerosols reflect and absorb solar radiation and alter the properties of clouds and thereby cause a large but highly uncertain cooling of the climate (Intergovernmental Panel on Climate Change 2007). Changes in aerosols over the industrial period strongly counteracted the warming effect of rising greenhouse gases by causing surface “dimming”.
It is now recognised that it is not only anthropogenic (pollutant) aerosols that can affect climate. Natural aerosols from wind-blown dust, forest fires, sea spray, and other sources contribute substantially to the total amount of aerosol in the atmosphere. These aerosol sources are highly variable and are known to respond to climate change. For example, forest fires will occur more frequently in warmer and drier conditions; increasing wind speed will produce more sea spray particles and dust; and trees emit more aerosol-forming chemicals like terpenes in warmer conditions. Our future climate may therefore be altered by the response of natural aerosol sources, leading to a different climate to the one currently predicted by climate models. This potentially important Earth system feedback was recently reviewed in Carslaw et al. (2010). We estimated the effect of some feedbacks, but we also identified several that were potentially very large but had not yet been adequately studied in models.
- Figure 1. Aerosol radiative perturbations due to climate-induced changes in natural aerosol between the present day and 2100. From Carslaw et al. (2010).
Objectives and approach
The aim of this PhD project is to quantify the effect of climate change on natural aerosol sources and the impact of these changes in aerosol on climate – the aerosol-Earth system feedback. Feedbacks will be quantified using the UK’s Earth system model at the Met Office: the Hadley Centre Global Environment Model (tinyurl.com/6zamw8b) combined with the UK Chemistry and Aerosol Model (www.ukca.ac.uk). There are many potential feedbacks to explore. An important first step will be to identify the most important feedbacks based on a combination of model simulations and observations. The most important feedbacks can then be studied in more detail by improving the physical, chemical and biological processes in the model. The ultimate aim will be to estimate future global and regional temperature and precipitation with and without aerosol-Earth system feedbacks. Recommendations will be made to the Met Office on how to improve the HadGEM model and how important these feedback processes are for their climate projections.
Suitable candidates
Earth system modelling will be of interest to students from varied backgrounds, including maths, physics, biology, chemistry, computing, environmental and geological sciences. The project offers the opportunity to specialise in certain areas according to interest, such as the responses of the terrestrial biosphere or the changes in global winds and sea spray.
Supervisors and the research group at Leeds
Prof Ken Carslaw is the Principal Investigator of the aerosol part of the UKCA project and the Global Model of Aerosol Processes. His group has published on a wide range of aerosol issues including atmospheric dust, marine aerosol, aerosol feedbacks, stratospheric aerosol, geoengineering, cloud processes, volcanic emissions and Arctic aerosol. Dr Dominick Spracklen is a NERC Advanced Research Fellow and a leading developer of the GLOMAP model. His research interests are in natural aerosol, especially forest emissions.
Role of the Met Office CASE partner
This project has been identified as a potential CASE project with the Met Office Climate Chemistry and Ecosystems Group. The Met Office is developer of the UK Earth System Model HadGEM. Leeds has had a long cooperation with the Met Office in the development of the aerosol component of the model. The outcome of this project will be of great interest to the Met Office because it has the potential to alter their climate projections and affect the way they develop the model in future. The student will have the opportunity to spend significant periods of time at the Met Office working with specialists in Earth system models. The student will benefit by gaining first-hand experience of developing, using and evaluating one of the world’s most sophisticated climate models.
Training
Students will be trained in the use and development of climate models, data analysis, visualisation and statistics. The large research group provides a network of skilled students and postdocs who support the development of new PhD students. A dedicated support scientist (Kirsty Pringle) provides training and development in the group’s models. The Met Office will provide training in the set-up and analysis of the Earth system model. You can arrange to visit the group to see how we work.
References
K. S. Carslaw, O. Boucher, D. V. Spracklen, G. W. Mann, J. G. L. Rae, S. Woodward, and M. Kulmala, A review of natural aerosol interactions and feedbacks within the Earth system, Atmos. Chem. Phys., 10, 1701–1737, 2010