Premature alarm and misplaced scorn have greeted the Zero Carbon Bill.
On one side, agricultural lobby groups are alarmed at the provisional target range for reducing biologically generated methane by mid-century.
But there are opportunities for them to make the case that the target is unjustly stringent — through the parliamentary process and also via the Climate Commission the bill sets up.
On the other side, Greenpeace executive director and former Green Party co-leader Russel Norman appears to think that a court of law is the only place governments can be held to account.
The bill reflects the gravity of the climate challenge by setting a mid-century target for greenhouse gas emissions consistent with what would be required globally to limit warming to 1.5C.
It sets up a mechanism, centred on an independent Climate Change Commission, for translating that target into a series of quantified medium-term carbon budgets.
The framework aims to provide the policy stability and certainty that businesses and investors need if a low-carbon future is to happen, while being flexible enough to adapt to a changing information flow over the next 30 years.
The legislation sets a target of net zero emissions by mid-century for the long-lived greenhouse gases, especially carbon dioxide and nitrous oxide, but carves out for separate treatment biological emissions of methane, mainly produced by belching sheep and cattle.
As introduced, the bill sets a target of reducing biological methane emissions by 10 per cent by 2030 and by between a quarter and a half by 2050.
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The agricultural lobby groups say that range — drawn from what the Intergovernmental Panel on Climate Change considers is needed globally — is way too tough.
They cite the conclusions of the Parliamentary Commissioner for the Environment in support of a gentler rate of decline.
While scientific opinion appears divided, the disagreement is not about the physics but about the relevant objective and timeframe for policy.
Methane is a potent but short-lived greenhouse gas. For those focused on the next 20 or 30 years it is the "potent" that matters; for those taking a longer-term perspective it is the "short-lived" part.
This debate will no doubt play out in the select committee process ahead.
Initial comments from the Leader of the Opposition, Simon Bridges, suggest some adjustment of the methane target may prove to be the National Party's price for supporting the bill.
That support is crucial. If the legislation is to be effective, the framework it sets up has to survive changes of government.
In any case, as it stands the legislation requires the 2050 targets to be reviewed when setting medium-term emissions budgets for 2036 onwards — something which would have to be done in the mid-2020s — or whenever the Climate Change Minister requests a review.
The grounds for review are drawn widely. There must be "significant" changes to at least one of these factors: global action on climate change; scientific understanding of climate change; New Zealand's economic or fiscal circumstances; New Zealand's obligations under relevant international agreements; technological developments; or distributional impacts (including generational equity).
And we can be sure a lot will change over the coming three decades. After all, 30 years ago hardly anyone had heard of global warming. No-one had heard of the world wide web; it was still a gleam in Tim Berners-Lee's eye. The Berlin wall still stood.
And if you drove around New Zealand you would have seen a lot more sheep and fewer dairy cattle than we do today.
That is relevant to the debate about the methane target. Land use will change. Some of it in response to climate change itself, and some in response to price signals: not only emission prices (which farmers cannot expect to escape indefinitely) but also prices that reflect changing consumer preferences.
Which will prove the stronger trend: a growing global middle class with a taste for the traditional foods of affluence, or the view which seems to be taking root that eating meat is some sort of planetary vandalism?
It would not be surprising if down the track New Zealand produces less butter and more avocados, for example, or less beef and lamb but more free-range pork.
Nor should we discount the potential for advances from research under way into animal genetics, pasture species, or intervention in the complex microbiology of the rumen.
The Biological Emissions Reference Group, set up by the previous Government, and on which industry bodies were heavily represented, concluded in its report last December that "[If] there was widespread adoption of currently available mitigation options (mainly farm management practices) an up to about 10 per cent reduction in absolute biological emissions from pasture-based livestock is possible."
But it warned that farmers' ability to implement such practices varied widely, and while some might achieve such reductions without significant negative impacts on profitability, for others the impact could be large. Cuts of more than 10 per cent would require a mix of on-farm mitigation and land-use change.
It canvassed the views of the NZ Agricultural Greenhouse Gas Research Centre and other experts and found "Medium-high confidence that a methane inhibitor for grazing systems that can deliver a 10 to 30 per cent reduction in biogenic methane will be available by 2030, and high confidence that one will deliver between a 30 and 50 per cent reduction by 2050.
"Modelling indicated that when all mitigation options assessed by the NZAGRC are combined into packages, and assuming various rates of adoption of each practice by farmers, overall biological emissions in the future could potentially be reduced between 10 and 21 per cent by 2030, and by 22 to 48 per cent in 2050, relative to [Ministry of Primary Industries] baseline projections."
Finally, what are we to make of Dr Norman's problem with sub-part 5 of the bill which tells us that the 2050 target and the stepping stone emissions budgets are not enforceable in a court of law? No remedy or relief is available for failure to meet the 2050 target or an emissions budget. A declaratory judgment is the most a court can do.
Does that mean the legislation is toothless and futile? Hardly.
The medium-term budgets are there to guide public policy across a broad front, not least the caps in the emissions trading scheme. Those caps deliver binding obligations on businesses which are points of obligation under the scheme.
And at the national level the regime is all about transparency. Accountability occurs in Parliament, in the media and ultimately at the ballot box.
Polling by Horizon Research has found a clear rising trend in public concern about climate change.
In 2006 only 3 per cent of those polled thought climate change was an urgent problem and another 16 per cent rated it "a problem now".
This year 43 per cent think it is an urgent problem and another 26 per cent a problem now, while 24 per cent consider it either a problem for the future or not a problem.
That is a trend more likely to strengthen than reverse.
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