AUSTRALIA - JAPAN SYMPOSIUM
AUSTRALIA - JAPAN SYMPOSIUM ON EARTH SYSTEMS SCIENCE
AND ON NANOMATERIALS
Canberra, 21 November 2006
Have Australian rainfall and cloudiness increased due to remote effects of Asian anthropogenic aerosols?
Dr Leon Rotstayn, CSIRO Marine and Atmospheric Research
Dr Rotstayn is a Principal Research Scientist at CSIRO Marine and Atmospheric Research, Aspendale, Victoria.
His main research interests are in global climate modelling, especially regarding the roles of aerosols and
clouds in climate change. In 2002, he was awarded the Frederick White Prize by the Australian Academy of
Science. Dr Rotstayn's work on global aerosol modelling has involved a substantial collaboration with the
team of Professor Joyce Penner at the University of Michigan in the USA. A recent member of that team (and a
contributor to the work being presented) is Dr Akinori Ito, now based at the Frontier Research Center for Global
Change in Yokohama.
Observations of Australian rainfall and cloudiness since 1950 show increases over the northwestern
and central parts of the continent. Transient GCM simulations forced only by changes in greenhouse
gases have generally not reproduced these increases. It is shown that including anthropogenic aerosol
changes in 20th Century simulations of the CSIRO GCM gives increasing rainfall and cloudiness over most
of Australia during 1951-1996, whereas omitting this forcing gives decreasing rainfall and cloudiness.
The pattern of increasing rainfall when aerosols are included is strongest over northwestern Australia, in
agreement with the observed trends. The strong impact of aerosols in the GCM is primarily due to the
massive Asian aerosol haze, as confirmed by a sensitivity test in which only Asian anthropogenic aerosols
are included. The Asian haze alters the meridional temperature and pressure gradients over the tropical
Indian Ocean, thereby increasing the tendency of monsoonal winds to flow towards Australia. The
results
suggest that inclusion of Asian aerosol forcing is essential in future modelling of Australian
climate
change.
