Washington: Former California governor Jerry Brown has blasted the Australian government's "utter and absolute" denial of the threat of climate change at an event warning the world is closer than ever before to a man-made apocalypse.

The Bulletin of the Atomic Scientists on Thursday (Friday AEDT) announced it was moving its famous Doomsday Clock closer to midnight than at any point in its 73-year history because of the growing risk of climate change, nuclear war and disinformation.

Several speakers at the announcement in Washington DC held up the Australian bushfire crisis as an example of the extreme and deadly weather events that will become more common unless the world dramatically reduces its carbon emissions.

Brown, who oversaw the response to California's most destructive wildfire crisis in 2018, told The Sydney Morning Herald and The Age he had no hope the Morrison government would become a global leader on tackling climate change.