Leaders attending the G20 summit in Brisbane may not get to talk much about climate change but it might be harder to avoid discussing the weather.

The mercury is forecast to climb to 40 degrees on Sunday in Brisbane and in suburban areas to reach 43 degrees as a heatwave settles over the eastern edge of Australia.

Scorcher: Hundreds of tourists and Brisbane locals spend their G20 public holiday at Streets Beach on Brisbane's South Bank. Credit:Jenelle Stafford

Brisbane's record for the month goes all the way back to November 18, 1913, making any new peak a once-in-a-century event, the Bureau of Meteorology said.