



''Statistically, there is a one in 500 chance that we are talking about natural variation causing all these new records,'' said Will Steffen, the report's lead author and director of the Australian National University's Climate Change Institute. ''Not too many people would want to put their life savings on a 500-1 horse.''

The statistic comes from tallying up known weather records from around the world and measuring the likelihood of record-breaking extremes happening without the influence of extra energy accumulating on Earth due to the build-up of greenhouse gases.





The past summer has been the hottest in Australian records. In the 102 years of uniform national weather records, there have been 21 days when the entire continent averaged more than 39 degrees - and eight of those took place this year.

Rainfall extremes have also smashed records, particularly along the east coast, with more rain contributing to floods and less to watering crops. The effects have also continued into autumn, with parts of Sydney experiencing a month's average rainfall in the past three days.

The intensity of the weather was considered highly unusual because it took place in a year without an El Nino cycle - a periodic phase of warm, dry conditions that pushes up temperatures. The previous three hottest summers recorded in Australia all took place in El Nino years.

Australia does not exist in a bubble and extremes here have been mirrored around the world. The US also had the hottest summer on record in 2012.

''In summary, there is now an ongoing fundamental shift in the climate system,'' the commission's report said.

''It is highly likely that extreme hot weather will become even more frequent and severe in Australia and around the globe over the coming decades.

''The decisions we make this decade will largely determine the severity of climate change and its influence on extreme events for our grandchildren.''
