CURT STAGER is a reformed climate sceptic. The US writer and scientist spent years scoffing at what he believed were the alarmist predictions of some of his peers. ''A lot of scientists have gone through the same process - I think even Tim Flannery went through the same thing.''

His questions concerned the fact the world's climate has changed so dramatically in the past, without any help from humans, that the current changes seemed unremarkable.

Stager's ''road to Damascus'' moment came a decade ago, when he was deep in correspondence with his friend Bill McKibben, a US environmentalist who later founded the 350.org movement to call for deep greenhouse gas cuts.

''I was like Bill's nemesis for a while, in a friendly way,'' he said. ''Eventually he challenged me to have a close look at the latest data, and right away it became obvious that something different was going on.''

The product of Stager's conversion is his new book Deep Future , which looks at the impacts of global warming as they cascade through the next 100,000 years.

''The good news is that it's not going to kill all of us. The bad news … well, there's plenty of bad news,'' he said.

His thesis is that people living today are inhabiting a pivotal point and will be responsible for changes that will take many millenniums to be felt.

Stager is appearing at several events at the Sydney Writer's Festival, including a panel discussion between environmental writers, to be held at Sydney Town Hall at 8pm on Friday, May 20.