The Ministry for Primary Industries (MPI) advised the Government that a methane reduction target of 25 percent by 2050 would be practical for the Zero Carbon Bill - but it was ignored.
Despite the advice from MPI, the legislation - announced in May - included a methane reduction target ranging from 24-47 percent by 2050, which has since been hotly contested.
Advice from MPI in November said a methane target of 25 percent below 2016 levels in 2050 would be consistent with the objectives of the Paris Agreement.
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New Zealand signed up to the Paris Agreement in 2015, agreeing to keep global average temperatures below 2degC. That was updated in October last year by the International Panel on Climate Change (IPCC) to 1.5degC.
The Minister for Climate Change, James Shaw, said in a statement that the target suggested by MPI, as well as advice from the Climate Change Executives Board and Parliamentary Commissioner, would "not meet the 1.5degc limit".
"The upper targets that they suggested do not meet that 1.5degC limit that the IPCC says we need to meet to avoid catastrophic impacts of climate change."
The Climate Change Executives Board, made up of the CEOs of departments with an interest in climate change policy, recommended last year that the methane reduction target is set in the range 22-35 percent below 2016 levels by 2050.
And in his August 2018 paper, Parliamentary Commissioner for the Environment Simon Upton said if New Zealand wished to ensure methane contributed no additional warming, emissions would need to reduce by 10-22 percent below 2016 levels by 2050.
Shaw said: "The problem with the MPI advice, the Climate Change Executives Board advice and that of the Parliamentary Commissioner is that they are not talking about targets to stay with no more than 1.5degC of warming above pre-industrial levels."
The National Party has opposed the Government's methane reduction target, with the party's climate change spokesperson saying it will have "perverse effects on the primary sector".
Dairy New Zealand has also disputed the Government's target, asking at select committee that it be set at up to 24 percent and regularly reviewed against robust criteria.
Chief executive Dr Tim Mackle said at select committee last month: "A 47 percent methane reduction target is simply setting farmers up to fail, if the tools are not available."
MPI made a similar claim in its advice to the Government. It said 25 percent would "represent a realistic emissions reduction that can be achieved with currently known technologies and avoiding significant land use change".
"Emissions reductions beyond 25 percent could be achieved at reasonable cost if there were breakthrough in methane mitigation technologies," MPI said.
"We therefore recommend that the target be periodically reviewed by the Climate Commission to ensure that the target keeps pace with the development of mitigation technologies and their cost."
Shaw acknowledged that the Zero Carbon Bill factors in that the independent Climate Change Commission should conduct a review in 2024 of its longer term biological methane target range.
He said it will take account of New Zealand's progress on emissions reductions, economic and other factors.