Russian president said: "We should think about how to stop this tragedy."
The virtual summit is set to be held on Wednesday.
"Did you ever think you’d be sitting at a G20 conference where everyone was preoccupied with the notion of global warming?” the president asked.
Western leaders have been keen to get back on cordial terms with President Xi Jinping.
All eyes have been on the UK's third prime minister this year.
As fires threaten Sydney, the nation's deputy prime minister dismissed “raving inner city lunatics” over concerns that climate change could be worsening the disaster.
"I am not saying that the Salisbury incident is the way to do it. Not at all. But traitors must be punished," Russian president tells FT.
The president wagged his finger at the Russian leader and told him not to meddle in the US election.
German Chancellor Angela Merkel was seen visibly shaking for a second time in two weeks. When asked if she would be attending the G20 summit in Japan starting on Friday, her spokesperson said, "Everything is taking place as planned. The chancellor is well." In the first incident, while visiting Ukrainian President Volodymyr Zelenskiy, Merkel’s spokesperson said the chancellor was dehydrated and was better after drinking some water.