The Government will take a highly conditional pledge to cut New Zealand's greenhouse gas emissions by 2030 to 11 per cent below 1990 levels - and therefore about 28 per cent from current levels - to the Paris climate conference in December.
The conference is intended to agree to a global deal to curb emissions more ambitious and wide-ranging than anything international negotiations have yet accomplished.
Climate Change Minister Tim Groser said the target is expressed as a cut of 30 per cent from 2005 levels to make it more readily comparable to the approach of the United States and Canada.
"It is a significant increase on our current target for 5 per cent below 1990 levels by 2020."
The Greens have been calling for a cut of 40 per cent from 1990 levels.
"If all countries followed New Zealand's lead, catastrophic climate change would be the result," said Green MP Kennedy Graham.
The target covers all sectors and all greenhouse gases, so does not exclude agricultural emissions, but as the consultation document the Government put out foreshadowed it will be hedged with conditions.
Because of the importance of land use and forestry to New Zealand's emissions profile, acceptable rules about how those are to be accounted for are an important caveat. The proposal specifically cites the "need to manage multiple objectives, including global food security".
Another condition attached to the 11 per cent target is unrestricted access to global carbon markets. This would allow New Zealand to meet its target - 80 per cent of it, the modelling suggests - by the purchase of carbon credits which represent emission reductions which have occurred somewhere else in the world more cheaply than any options available within New Zealand.
The environmental integrity of those credits, and the robustness of measures to preclude double counting, are crucial.
"The likely cost to the New Zealand economy of meeting the 2030 target in terms of GDP is greater than that implied by other parties' tabled targets," the proposal says.
"This is due to a number of factors, such as already achieving a high level of renewable electricity generation, and almost half of New Zealand's emissions originating from agriculture." The Herald understands, however, that Treasury modelling to back up the claim this is a comparatively onerous target is not likely to be released until after the Paris conference.
Groser was optimistic research into reducing emissions from livestock and bringing down the cost of electric vehicles would bear fruit.
But the proposal said the transformation of the transport and agricultural sectors would take longer than the 10 years to 2030.
Groser said: "The Government will adopt an appropriate mix of policies to ensure the target is met. In particular, we will begin a review of the emissions trading scheme this year, which will include scope for further public discussion on what New Zealand will do domestically."