A report delivered to Whanganui district councillors says temperatures in the district could rise by 1.1C by 2040 with as many as 12 more very hot days across the year.
Whanganui District Council senior policy adviser Jasmine Hessell and research and engagement policy adviser Kirsty Milham delivered the report to the council's infrastructure, emergency management and climate change committee as it looks to develop a climate change strategy.
Councillor Rob Vinsen was surprised to read that sheep in the Whanganui District account for 32 per cent of its climate-changing emissions and transport only 22 per cent.
"Sheep more than transport in our area. That can't be true," he said.
Committee chairman Alan Taylor said methane emitted by sheep was more potent than carbon dioxide as a climate-changing gas in a "climatology 101" lesson.
Vinsen went on to look at predicted sea level rise; a 0.5m rise by 2060 is predicted under the most extreme climate change scenario.
He said he had found other climatologists with less extreme predictions.
Councillor Graeme Young said the level of the river changed that much every day, as the tides change.
But small changes in sea level could make a big difference when combined with a flood and storm event and high tide, deputy mayor Jenny Duncan said.
Whanganui mayor Hamish McDouall said councillors should do some research before "shooting from the hip".
He said the city of Jakarta was even now being moved to avoid sea level rise, and Kāpiti residents who fought against a determination of coastal inundation would be losing the value of their flooded houses.
Climate change was happening now and accelerating, Taylor said.
The council's infrastructure team was adapting, manager Mark Hughes said. It might have to pump stormwater out over stopbanks if the river was high enough to back up stormwater outlets.
Hessell and Milham's report said Whanganui's average temperature could increase by as much as 1.1degC by 2040, with as many as 12 more very hot days across the year.
Currently there are an average 18 nights where the temperature dips below zero, and that could reduce to just seven. Rainfall could reduce 1 per cent in autumn and increase 5 per cent in winter.
There is likely to be more intense rain, especially in short cloudbursts. More summer droughts are likely, especially inland. The intense rain will increase hill-country erosion, and storms will be more intense.
Milham and Hessell hope to have a climate change strategy drafted, consulted on and adopted by December. Duncan called that an audacious goal, and Taylor said a rate had yet to be struck to finance it.
The infrastructure committee was the right place for climate change to be discussed, councillor Kate Joblin said, because it could be related to Whanganui infrastructure there.
The officers are working closely with iwi, and the next stage will be a joint climate workshop.