Climate scientist James Renwick says the declaration of a "climate emergency" by some councils only matters if it is followed by action.

Renwick, who is giving a second talk on global warming in Whanganui this month as part of the Whanganui Science Forum, said it could be frustrating to talk about climate change without seeing urgent action.

Whanganui District Council this week deferred a debate around acknowledging a climate emergency and it will be held at a later strategy and finance meeting.

Renwick said the audiences at his talks were usually self-selected and know a lot about climate change.

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He'll give a quick re-cap for those new to the subject.

Climate change had not really hammered New Zealand yet, though marine heatwaves and tropical cyclones had come close, he said.

This is with the current 1C average temperature rise.

Renwick said a bigger rise could destroy the global economy and displace billions.

"Where do we stop is not a scientific question. It's how much pain do we endure, that's the real question."

He gets asked to talk publicly about climate change a lot.

"I don't want to stop. I think it's important to keep raising awareness, but it feels a bit dispiriting sometimes," he said.

Telling people what they can do was difficult because our society was based on use of fossil fuels which meant moment "you have to punish yourself to be green", when the opposite should be true, he said.

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"It should be difficult to have a really high-emissions lifestyle."

Local authorities declaring a "climate emergency" at least keep people talking.

"I'm hoping most bodies saying these things are actually swinging into action, but I don't know. It isn't obvious."

*The talk is on July 30, at 7.30pm in the Davis Lecture Theatre at Whanganui Regional Museum. It will cost Whanganui Science Forum members $4, and $5 for others.