Most major Australian cities will be far hotter than forecast in coming years, as a lack of vegetation creates "heat islands".

The report, Temperature Check: Greening Australia's Warming Cities, commissioned by the Australian Conservation Foundation, found green spaces in almost all major cities had declined in the last decade.

Our research shows increasing urban vegetation will become essential for our three largest cities — Sydney, Melbourne and Brisbane — to reduce serious heatwave impacts by 2060-2080," said the report's author, Dr Lucy Richardson from the Monash Climate Change research communication hub.

In 2020, Brisbane sat at 54 percent green cover, comparing greener than Melbourne and Sydney.