The global climate system, warmer and moister than it was 50 years ago, is bringing increased heat and making extreme weather events more frequent and severe, the commission said in a report Wednesday.
Last summer was Australia's hottest ever, including the longest and most extreme heat wave on record, the Bureau of Meteorology said.
The effects of extreme weather have a dramatic impact on communities and infrastructure, with the cost often running to billions of dollars, Australian officials said.
"Only strong preventative action now and in the coming years can stabilize the climate and halt the trend of increasing extreme weather for our children and grandchildren," China's official Xinhua News Agency quoted the climate commission's chief Tim Flannery as saying.
Australia can expect more heat waves, fires, cyclones, heavy rainfall and drought unless action is taken, Australian Greens party leader Christine Milne said.
The release of the report "should end climate denial and put higher greenhouse reduction targets and adaptation to existing warming on the political agenda," she said, calling for the restoration of funding for planning to deal with the issue.
"The cost of not acting on climate change is greater than the cost of acting."