Numerous experts have linked the vast scale of Australia's bushfires to climate change, noting that unprecedented heat and drought created conditions for fires to flourish.

But as Australians choked on smoke and discovered their homes had been destroyed this summer, a different message was spreading on Facebook.

Counter-theories gained traction online that blamed the fires on arsonists, failed hazard reduction policies and even lasers designed to clear a path for a high-speed railway. These theories are untrue or misleading, and have been used to undermine the mainstream consensus on the role of climate change.

And Facebook — the platform conspiracists are using most effectively to muddy the waters or straight-up deny climate change — is doing little to stop the spread.