Deep cuts to staff and funding by the NSW government have largely dismantled the state's ability to investigate and prepare for the effects of climate change such as more frequent extreme fire weather, a former senior scientist with the government said.

Peter Smith, who led the state's climate change science group until March, said his team of 10 had been slashed to just three whose work remained climate-focused. A similar cut had been made to a separate team of 10 working on climate adaptation, he said.

''There's been more than a 50 per cent cut in the numbers of staff whose primary focus was climate change,'' Dr Smith said in his first media comments since leaving the role. ''The [Office of Environment and Heritage] was being downgraded anyway from a super department under the previous government to being an office attached to the premier's [department]. The reduction in the climate change [section] was even more significant than the general reduction.''

Dr Smith, who now works as an adviser on United Nations projects, was a contributor to peer-reviewed research reports that found Australia was already facing an increase in bushfire dangers. The shift was particularly clear in spring, with national mean temperatures rising 0.9 degrees since 1960.