Arctic climate change: the vital role of pollution and climate feedbacks

Project Summary

Figure 1: Regional differences in Arctic aerosol sources (Schmale et al., 2021), with each region noting potential future changes.

The climate of the Arctic is changing faster than any other region of the planet. Although greenhouse gases are the main driver of global warming, the accelerating rise in Arctic surface temperature, and seasonal loss of sea ice, have a more complex explanation. Changes in air pollution (aerosols) and local feedbacks between aerosols, clouds, and sea ice are important contributing processes, but they are poorly understood due to sparse observational data coverage across the region. This limited understanding hinders our ability to represent these small-scale atmospheric processes appropriately in climate models.

Persistent low-level cloud cover in the Arctic summer and autumn can have a dramatic effect on the surface temperature. Observations and model simulations show that the properties of these clouds are strongly influenced by aerosols, which act like seeds upon which cloud particles can form. In particular, because summertime aerosol concentrations are often extremely low, the existence of clouds can be ‘aerosol limited’ (Mauritsen et al., 2011; Tjernström et al., 2014). Both natural and anthropogenic aerosol sources are likely to change substantially in a future climate as sea ice cover and anthropogenic emissions change (Fig. 1; Schmale et al., 2021), which is likely to alter cloud properties and the surface energy balance.

This PhD project aims to understand how aerosols control the behaviour of Arctic low-level clouds, how their behaviour may change in future, and what impact any changes will have on the climate of the Arctic. The research will involve running advanced aerosol and cloud models from the scale of a few metres up to global. Model simulations combined with extensive recent observations will be used to understand how the climatic effects of Arctic clouds are altered by aerosols from air pollution, as well as changes in aerosol from natural sources as sea ice retreats.

This project provides a great opportunity to become involved in Arctic research at a time when several international initiatives and major projects are coordinating programmes of Arctic research and making extensive measurements that can be used to test climate models. New understanding from this research will feed through to improvements in the UK Met Office climate model, providing the student an opportunity to contribute directly to improved Arctic climate projections.

Objectives:

  • Develop Met Office models to incorporate latest knowledge of aerosol and aerosol-cloud processes in the Arctic.
  • Analyse field measurements and satellite observations of clouds, aerosols, and surface radiation to test and improve the models.
  • Evaluate how air pollution transported from afar interacts with Arctic low-level clouds, modifying their internal structure and radiative properties.
  • Improve our understanding of how Arctic aerosols respond to reductions in sea ice cover and how changes in aerosols and clouds could affect the sea ice in future.
  • Explore the effect of new understanding and improved modelling capability on Arctic climate using the UK Earth System Model.