Climate Change Minister James Shaw says response to Emissions Trading Scheme reforms has so far been muted.

Climate Change Minister James Shaw expects some businesses will be shocked by the Government's latest proposals for tackling carbon emissions.

"When you see the actual numbers, people go 'oh crikey' – that's what that means."

But he is not expecting them to come up with many fresh arguments.

There is just a month left for submitters to have their say on proposals that Shaw and Energy Minister Megan Woods put forward on December 19 and that are designed to give the Emissions Trading Scheme (ETS) much more bite.

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The proposed measures including limiting the total amount of carbon credits available for auction that provide the "right to emit" a tonne of carbon-dioxide emissions, introducing a minimum price of $20 for each credit, and doubling a cap on their maximum price to $50 a tonne.

The changes could result in businesses having to pay up to $4 billion for the 80 million new carbon credits that are expected to be released for auction up until 2025, rather than the $2b or so that they would pay at current market prices.

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But Shaw says the response has so far been "largely very muted".

He puts that down to the fact that the ETS has effectively been up for consultation since 2015, when former National Party climate minister Tim Grosser kicked off his own review.

"There are no surprises in here," he says of the Government's discussion document.

"Everything we went out to consult on – with the exception of agriculture which got a lot of airtime last year – has been consulted on a number of times over the past four or five years and all of the emissions-intensive industries have been involved at every step."

National Party climate spokesman Scott Simpson has said it was "poor form" for the Government to drop such an important consultation document days before Christmas.

But Shaw says he is not anticipating "a huge amount of kickback".

"I would imagine some of the more exposed businesses looking at the document that we released in December will say 'that's quite tough'. But I think they knew that."

"Having spent so long engaging with industry to this point, I'd be surprised if there is anything radically different that was said that we didn't know about already."

NATALIE CROCKETT/STUFF A 7-year ban all road traffic, or a 5-year ban and another billion trees, would probably not be enough to generate the extra carbon savings the Government needs to find by 2030.

Charging a higher price for carbon emissions is the main tool the Government is relying on to meet New Zealand's obligations under the Paris Agreement, and then its goal of zero net emissions –excluding agricultural methane – by 2050.

The Ministry of Foreign Affairs and Trade states that the former National government committed to cutting New Zealand's carbon emissions by 30 per cent from their 2005 level, by 2030, when it signed up to the Paris climate accord.

But the detail of what was actually agreed is more complicated than that.

The broad goal is to cut New Zealand's net emissions to 70 per cent of its 2005 gross carbon emissions.

The "gross to net" target has been labelled a cheat by some environmentalists.

But there are different ways of calculating net emissions, and the Paris target excludes many forestry offsets that have been counted in Statistics NZ's net emissions totals, making it a tougher target than could otherwise be assumed.

The target is also framed around a 10-year carbon budget, rather than just being about the emissions New Zealand produces in 2030 itself.

But the nub of it is that the country is faced with knocking 102 million tonnes (Mt) off its currently forecast net carbon emissions of 703Mt during the 10 years between 2021 to 2030.

That can be achieved by cutting emissions and by planting forests and – potentially – by buying international carbon credits to help make up any difference.

To put that 102Mt reduction in context, the Government's "billion trees" initiative is already factored into the current 703Mt net emissions forecast and is expected to soak up a total of between 10Mt and 30Mt of carbon over that 10-year period.

Road transport emits just under 14.5Mt of carbon annually.

So even if the Government planted an extra billion trees on top of the current billion planned, and banned all cars and trucks from the roads for five years from next year, those measures on their own probably wouldn't be enough to meet its 2030 Paris target.

The Government is currently suggesting a provisional carbon budget of 354Mt for the period from 2021 to 2025, which would leave a budget of just 247Mt for the five years from 2026 to 2030.

After 2030, the pace of reductions could ease off a little and still be on track for the 2050 "zero carbon" goal.

Shaw pauses when asked whether the implied goal for 2026 to 2030 is realistic.

"I believe so, yes. It will be challenging, however.

"It is tough and if we'd started to reduce emissions back in 2015 when we signed the Paris Agreement or – frankly – back in 2008 when Helen Clark said we wanted to be 'net zero' by 2020," it would be a lot easier than it is now."

GETTY IMAGES New Zealand's contribution to the Paris Agreement was based on cutting net emissions in 2030 to 30 per cent of gross emissions in 2005, but that target is tougher than some estimates of NZ's net emissions suggest, as it excludes a big chunk of forestry offsets.

Shaw explains that is why the Government is consulting on reopening the ETS to international carbon credits from 2025.

That would end a moratorium that was put in place in 2015 in the wake of scandals surrounding the purchase of dubious credits bought by New Zealand companies from Russia and Ukraine.

The Government's consultation documents envisage it might need to enter the international carbon credit market itself.

That would be to build up a reserve of carbon credits that it might need to sell to businesses to prevent the New Zealand price of carbon credits rising above the proposed $50 cap.

But Shaw says any credits sourced from overseas would need to come from countries that appeared on track to meet their own Paris targets.

"We haven't stated that as an explicit criteria, but all of the conversations that we have had have been along those lines."

That means that if no countries were on track to meet their Paris targets, there might be no international carbon credits with which to establish a reserve and potentially no credits available at the $50 price cap, raising the possibility of some form of rationing.

In other words, businesses might be willing to pay more than $50 for credits, but need to stop production instead because there were none to buy.

James Shaw hopes Australia's bushfires might help do some of the persuading.

Shaw responds that the $50 cap could change "and almost certainly will".

"I imagine the Climate Change Commission will come up with its advice around that."

He agrees the Government could do more to persuade people to take the required level of action on climate change.

"If you look at the estimated 170,000 people that were marching on the streets last year asking us to do more, clearly they don't need persuading.

"But if you look at some of the resistance that we had in the agricultural community then 'sure, of course'.

"Are there constituencies that we could be doing more with? The answer to that is almost certainly 'yes'."

But the experience of the Australian bushfires was also changing the discussion, he said.

"In some parts of the country we had our own skies darken and the sun turn red.

"We can shove scientific reports at people until they are blue in the face, but it is people's actual personal experience that is going to be more relevant to them.

"The question is does that personal experience shift in time for us to act fast enough."