Peter Dunne says Parliament, not the Government, should set New Zealand's climate change target.
The United Future leader wants a full debate, with all parties given equal access to the Government's scientific and economic data.
The Government last week announced what it called a "more ambitious" target of achieving a 30 percent reduction of 2005 emission levels by 2030.
It will submit the new target to the United Nations in December.
The current target is a 5 percent reduction of 1990 levels by 2020.
Mr Dunne says he's reminded of Mark Twain's aphorism: lies, damn lies and statistics.
"The new target is actually the equivalent of more than doubling the original target regarding 1990 levels [11 percent instead of 5 percent] but achieving it over a 25 percent longer time frame, by 2030," he said.
"Some critics actually say our target is really weaker, rather than stronger, than its predecessor."
Mr Dune says climate change is arguably the most important issue facing humanity.
"It should transcend the usual political hullabaloo," he said.
"Our policy response needs to go beyond the normal confines of consideration by ministers and officials behind closed doors... and for Parliament to make the ultimate decision regarding emissions reduction targets."