Mitigation of climate by reductions in air pollutants
Supervisors: Dr Dominick Spracklen (SEE), Prof Ken Carslaw (SEE), Prof Piers Forster (SEE) and Dr Jim Haywood (Met Office)
Background
Atmospheric particulates (aerosols) are a major cause of climate change. Over the industrial period, industrial and domestic emissions of aerosols have substantially altered regional and global changes in temperature. Aerosols reflect and absorb solar radiation and alter the properties of clouds and thereby cause a large but highly uncertain impact on climate (IPCC, 2001, 2007). Some aerosol types cool the climate, whilst others such as black carbon (soot) may warm the climate so understanding the impact of future changes to aerosol emissions is critical.
- Fig 1. Radiative forcing of climate over the industrial period from the Intergovernmental Panel on Climate Change 2007 assessment. The radiative forcing is a measure of the warming (positive forcing) or cooling (negative) caused by various changes in the atmosphere. The large blue bar shows the effect of aerosols on clouds. There are large uncertainties associated with this aerosol forcing that could be reduced if we understood better how cloud-forming particles are produced around the world.
The aim of this project is to understand how future changes in aerosol emissions will impact climate. The effects of aerosol reductions have previously been estimated, but we believe the models that have been used are too simplistic to get the magnitude and even sign of the climate effect right. In particular, soot emissions from different energy sectors vary enormously in their characteristics and therefore have different effects on climate. Models developed at Leeds (see http://researchpages.net/glomap) are now sophisticated enough to take into account the size, number concentration and chemistry of the different particles. Some particles are strong absorbers of solar radiation and may warm the climate, but at the same time they contribute to formation of cloud drops, which will act to cool the climate. The project will examine future emission reduction strategies and use the global aerosol and climate models to take account of these competing effects.
Objectives
1. Use state-of the-science global aerosol models to understand what factors control the long term change in cloud-forming aerosol particles. This will involve analysis of model results and observations of particle sizes, concentrations and chemistry.
2. Use an aerosol-chemistry-climate model to simulate the changes in cloud-forming particles over the industrial period.
3. Quantify the effect of aerosol changes on cloud radiative forcing and climate
4. Quantify how future emission changes will impact climate.
Potential for high impact outcome
The effect of aerosols on clouds is one of the biggest uncertainties in climate change over the industrial period. There are several things that need to be done to improve our understanding. A key step is to be able to predict the global distribution of cloud-forming particles, and how it changes over time. Models are only now able to do this, so there’s a great opportunity to exploit them and substantially improve our understanding of factors controlling climate change.
There is now considerable policy interest in controlling black carbon (soot) emissions to slow the rate of climate change. This project offers considerable potential to contribute key scientific knowledge to inform these policy decisions.
Training
You will benefit from working within an active and multidisciplinary group of scientists in the Aerosol Chemistry and Climate Group and the Physical Climate Change group. The groups have a long track record of developing and using climate and aerosol models, and has trained many PhD students who started from a very limited knowledge of computing. This PhD provides excellent opportunities to learn how to develop and run advanced climate models that are used in IPCC assessments by the Met Office. The group has a dedicated support and research scientist (Dr Kirsty Pringle) who can provide support and training in the use of the models. There will be an opportunity to attend the NCAS Earth System Science summer school at the start of the PhD.
This project has been approved as a "potential CASE studentship" by the Met Office. Three Met Office CASE studentships will be awarded at the School of Earth and Environment in the 2012 competition, and will be assigned to those students whose applications are ranked highest.
Further reading
We recommend that you visit the global aerosol modelling web page and the physical climate change group web page to find out the sorts of exciting things we study and the kinds of models we have developed: http://researchpages.net/glomap and http://www.see.leeds.ac.uk/research/icas/physical-climate-change-group/