The former commissioner for the environment says those who deny man-made climate change are not using science.
"People who say it's not real, they're not basing it on science, they're basing it on what they want to believe," Dr Jan Wright told The AM Show on Wednesday.
But it's not just deniers who are the issue - she says over-population is another problem.
"There are too many people," she said. "I don't want to offend the Catholic Church but there are far too many of us."
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Dr Wright says it's undeniable that humans are to blame for climate change.
"Humans have started to trigger a warming period," she said.
"The basic evidence is there, the sea has risen, the surface temperature of the earth has gone up - it's undeniable."
Radio host Sean Plunket disagreed in a segment later in the show.
"I'm a realist and a pragmatist. I don't think there's no scientific debate on climate change," he told The AM Show.
"Many of the predictions we have been given in the past 15, 20 years have demonstrably not come true."
He says while the climate is changing, it's always changed - and those who believe humans are causing the change are part of "a cult".
Despite deniers and over-population, Dr Wright says she isn't losing hope.
"I choose to believe that we haven't [come too far to change]," she said.
"This new climate commission, it's their job to tell the Government what it has to do to turn this down."
If changes aren't made, Dr Wright says New Zealand will miss the targets it set under the Paris Agreement "by a country mile".
The Paris Agreement is a promise New Zealand will reduce its greenhouse gases by 30 percent below 2005 levels by 2023.
"We're on target to miss that," said Dr Wright.