Polar Feedbacks between Ozone Recovery and Climate in the Southern hemisphere (Polar FORCES)

Project background

The Fourth Assessment Report of the Intergovernmental Panel on Climate Change highlighted the need to more accurately represent stratospheric processes in climate models in order to reduce uncertainties in future climate projections.

A 2010 report comparing leading chemistry-climate models notes that the recovery of stratospheric ozone will produce significant feedbacks to the surface climate of Antarctica and the Southern Hemisphere during the remainder of this century, both in terms of changes of the seasonal cycle and long term trends in temperatures and winds.

Australia is developing the capability for fully coupled chemistry-climate modelling through the Australian Community Climate Earth System Simulator (ACCESS). ACCESS incorporates the ‘UKCA’ chemical module (United Kingdom Chemistry and Aerosols model) that featured favourably in the 2010 model comparison report. Australia was not involved in the comparative modelling and, to date, development and implementation of ACCESS has focussed on numerical weather prediction and climate projections which have not utilised interactive stratospheric chemistry.

Implementation and use of the UKCA module has largely been left to the Australian university sector. To progress chemistry-climate modelling with ACCESS and to utilise key interests in the influence of ozone recovery¹ on Southern Hemisphere climate, the Australian Antarctic Division and the University of Melbourne are collaborating through a Postdoctoral Fellowship appointment.

¹ ‘Ozone recovery’ refers to the recovery of stratospheric ozone levels to pre-ozone hole levels as a result of international protocols to control ozone depleting substances.

Project objectives

To provide new analyses and advice on the effects of feedbacks from ozone recovery on Southern Hemisphere climate, this project seeks to:

1. Fully implement the UKCA chemical module in the ACCESS model environment for stratospheric studies and to conduct validation experiments by comparing ACCESS model outputs to standard scenario results and to historical observations on regional and zonal scales.
2. Assess specific climate-related processes of the Antarctic stratosphere and troposphere that provide important diagnostics of coupled chemistry-climate model projections involving ozone recovery. The assessments will involve analysis of observational data and climate model runs. The specific metrics and processes to be examined include:
   1. Metrics relating to the stratospheric polar vortex, including the size and strength of the vortex, and anomalies in temperature, wind velocity and ozone concentration.
   2. Long-term trends in the spatial pattern of total column ozone.
   3. The regional influence of small scale waves on Polar Stratospheric Clouds (PSCs) and stratospheric chemical processes.
   4. Regional influences of wave processes on transport in the upper troposphere-lower stratosphere (UTLS) region.
   5. Coupling between the stratosphere and troposphere revealed through variability and trends in the Southern Annular Mode.
   6. Regional trends in surface ultraviolet radiation from analyses of ACCESS model results and observations from radiation monitoring networks.
3. Where feasible, improve the representation of polar processes and composition scenarios in the ACCESS model. This may involve new representations of PSC microphysics and small-scale waves, and revised projections of greenhouse and ozone depleting gases.
4. Conduct new scenario-based model runs of ACCESS to examine the regional effects of ozone recovery for Antarctica and the Australian region.

Expected outcomes

The outcomes will include implementation of a new Earth system modelling capability for Australia, and peer-reviewed analysis on changes in Antarctic and Southern Hemisphere climate processes for scientific journals and advice to government.

The project will foster closer collaborative links with the trans-Tasman and international climate modelling communities through activities such as workshops on stratospheric chemistry-climate modelling and the Southern Hemisphere regional effects of stratospheric ozone recovery.

Measurements in the graphs above are by the Australian Antarctic Division and the Bureau of Meteorology. Data are available from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC).