Aerosols are micron-scale particles suspended in the atmosphere, and are derived from a variety of natural and anthropogenic processes. Aerosols interact with solar radiation, and also act as cloud condensation nuclei. Increases in anthropogenic aerosols have tended to cool Earth’s climate, partially counteracting the warming from greenhouse gases seen since the Industrial Revolution.
However, in the near future, it is widely expected that anthropogenic aerosols will decline steeply as we clean up harmful air pollution. This will add to the expected warming from further growth of greenhouse gases. This effect is already well known. However, recent results from our group (Zhao et al., 2019) indicate that cleaning up aerosols may also lead to a dramatic and disproportionate increase in heatwaves, an impact not previously appreciated. We think that this arises through impacts on clouds, via aerosol-cloud interactions, which induce important changes in the diurnal temperature cycle. Currently, we have only seen this effect in future projections from one model, and have little confidence in the details. In this project, we will explore the effect in past observations, and in a wider range of models.
Key research questions
• How do changes in anthropogenic aerosols affect the diurnal temperature cycle (DTC)?
• Can we use observations of past variations in the DTC, aerosols, and clouds, to improve the representation of aerosol-cloud interactions in models?
• How does this affect future projections of heatwaves?
A new reanalysis product, ERA-5, has recently been released, and provides global surface air temperatures at hourly temporal resolution, and 0.25 degrees spatial resolution, for the period 1979 to present-day. We will explore these data and document changes in the DTC and cloudiness. We will use independent data on past aerosol changes to relate aerosol, DTC and clouds. There have been strong regional differences in how aerosols have changed (e.g. cleaning up over Europe and N. America in recent decades, but worsening air quality over much of Asia), and we expect these changes to lead to different regional changes in DTC and clouds.
We will explore whether models correctly represent these aerosol-cloud-surface temperature effects, and refine model schemes as necessary. We will mainly use the UK Earth System Model (UKESM1), but also look at other models within the CMIP6 archive, to look at how different model schemes lead to different responses. We will quantify how these schemes impact on how heatwaves are represented in models.
We will assess future implications, again using UKESM1 and the suite of CMIP6 models. .
Zhao, A., Bollasina, M.A., Stevenson, D.S, 2019, Strong influence of aerosol reductions on future heatwaves, Geophysical Research Letters, https://doi.org/10.1029/2019GL082269
A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills.
Eligibility and qualifications
Only UK/EU citizens resident in the UK for at least 3 years prior to the start of the studentship. Further details and stipend are at http://www.ed.ac.uk/e4-dtp/how-to-apply/funding-and-eligibility
You should have, or be expecting to achieve, a good Honours or Master’s degree, or equivalent in a quantitative science background (physics, maths, computing, chemistry), with an enthusiasm for atmospheric science. You should be prepared to analyse very large datasets and run complex Earth System Models.
Applications must be made directly to the E4 DTP https://www.ed.ac.uk/e4-dtp/how-to-apply
by the deadline of 9 January 2020
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