While Prime Minister Jacinda Ardern is being feted by global leaders in New York for her optimistic climate change activism, back in Wellington her government's plans to extend the emissions trading scheme (ETS) to farming have stalled.

Ardern promised to end the 11-year exemption granted to farmers to keep them out of the ETS as part of the Government's coalition agreement, but on Tuesday Stuff revealed that those plans had stalled after ministers within the patchwork government were unable to agree on the details.

Government sources say a scheme to bring agriculture into the ETS had been unable to make it past Cabinet committee stage, the step before a final decision is made during a full Cabinet meeting.

This is despite consultation on the proposals finishing last month.

Climate Change Minister James Shaw said ministers were still discussing proposals and said delays were "not unusual" around complex policy. 

"This happens quite a lot where you've got a difficult issue that ministers will continue to talk about it until you get a resolution," Shaw said.

Yet while there is no explicit suggestion that the ETS changes would be dropped, the Government was anxious to have its ducks in a row to avoid a protracted battle with the farming sector when the plan was unveiled.

A pitched battle with agriculture could risk NZ First's support peeling away - the party relied on rural support at the last election and could see its votes draining to National.

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Unless the prime minister could ensure Cabinet passed the changes it might be a case of "do as I say, not as I do" on the international stage. Failure would play into the National party's narrative of Ardern as eloquent, but ineffective.

"The things that the prime minister has talked about, literally none of them have happened to date and I understand in terms of the coalition, they won't happen," National leader Simon Bridges told Stuff about the climate deal on Tuesday.

The Government's other key climate change policy, the Zero Carbon Bill, was currently making its way through Parliament and looked set to pass.

Stuff understood the ETS talks had stalled due to opposition from farmers, already smarting over a set of tough new proposals from Environment Minister David Parker to regulate water quality.

Farmers feared that being folded into the ETS would increase their cost of living, doing business, and be difficult and expensive to administer.

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On the first day of the UN leaders' meeting in New York Ardern promised that: "We are determined to show that we can be the most sustainable food producers in the world".

Agriculture is New Zealand's largest greenhouse gas emitter, responsible for nearly half of the country's total emissions, but it's been exempt from the ETS since the system was launched in 2008.

Last night in New York, Ardern said that farmers were leading the charge. 

"You've had already those from the sector, those leaders from the sector themselves bringing leadership together and committing that by 2025 they want to see a farm-by-farm pricing mechanism in place"

The Environment Cabinet Committee was due to next meet on Wednesday afternoon. Shaw said he expected a solution to be "sorted in the next couple of weeks".