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The government's own advice on repealing the oil and gas exploration ban says no new gas fields are likely to be discovered and developed in the next 10 years.
The latest modelling, urgently released under the Official Information Act and obtained by RNZ, says in the short term repealing the ban is unlikely to significantly bolster gas supplies from existing fields, either.
That makes the climate impacts of the law change smaller, but also shrinks any expected impact on the energy market.
Resources Minister Shane Jones has sold the law change as being needed to keep gas flowing and "keep the lights on", after supplies from existing gas fields dwindled sharply this year.
He responded to the latest modelling today by saying the repeal was "long term thinking" and a "contingency" in case big growth in renewable energy did not pan out.
"I really ask Kiwis to conceive this change to be in the vein of providing a contingency option, so this does represent another arrow in the quiver."
Asked if any new gas would arrive in time to make a difference, Jones said "you have to take a long-term view".
He said "no-one predicted" when Jacinda Ardern banned exploration in 2018 "that we would be dependent on Indonesian coal".
Asked if he thought existing gas fields would be producing more gas today - allowing less coal use - if it were not for the ban, he said: "Well, there's the geological reality in terms of existing fields."
He said the prospect and timing of any new gas supply "lies at the centre of a whole lot of conflicting forces", but there would be no legal impediment to it happening.
In response to RNZ's reporting, Greenpeace posted on X/Twitter that: "All that talk about 'keeping the lights on' was always just a smokescreen. The government's own advice was that repealing the exploration ban would likely see no new gas before 2035 anyway."
According to the modelling, the main short-term impact of allowing companies to explore for new supplies of fossil fuels off the New Zealand coast appears to be giving them the confidence to extend the life of their existing gas fields in the future. Those fields are already operating under existing permits.
The Ministry for Business, Innovation and Employment (MBIE) said it planned to publish the updated modelling on its website where submitters could see it, however it was not immediately findable there when RNZ checked on Monday morning.
Asked if the modelling would be shared with the public, Jones said he would chase that up with MBIE. There is one day left for the public to make submissions before the deadline of 11.59pm on 1 October.
Little short-term boost to gas supplies means smaller climate impact
The analysis shows Government officials believe that undoing the ban will encourage fossil fuel companies to release more of the gas available to be extracted from their existing fields. That's because officials think those companies will have more confidence in investing in oil and gas, without the ban.
The Crown Minerals Amendment Bill reverses a 2018 ban on exploring for new oil and gas fields, and makes other changes to make fossil fuel exploitation more attractive.
Carbon emissions from the law change are now projected to be much smaller than previously suggested, because of the long timeframe before any significant boost to gas supply
Originally, MBIE's climate impact assessment found undoing the ban would result in an extra 51 million tonnes of planet-heating emissions being pumped into the atmosphere in the years to 2050.
That is almost as much greenhouse gas as New Zealand's economy as a whole produces in a year.
Short term, MBIE originally estimated that between now and 2035, moves to encourage oil and gas extraction would add 14 million tonnes of carbon dioxide emissions to the country's tally, roughly the amount of greenhouse gas New Zealand's cars and trucks produce in a year.
However, the latest modelling estimates just 1.6 million to 2.4 million tonnes of extra emissions - total - could be released out to 2035 as a consequence of undoing the ban.
Officials tested the impacts of two scenarios: companies successfully tapping 30 percent of what is known as "contingent reserves" of gas (gas in existing fields, that can be extracted under existing permits) versus companies extracting 60 percent of those reserves.
The lower emissions figure is if 30 percent can be extracted and the higher figure is if 60 percent of those reserves are produced.
New Zealand's emissions are expected to rise as a result of undoing the ban, even after taking into account the fact that electricity companies may burn less coal if they can secure more gas.
That's because the added emissions from burning more gas outweigh any savings from burning less coal.
New supply "unlikely" before 2035 - MBIE
In MBIE's words, "the repeal of the oil and gas exploration ban may lead to greater investment in existing gas fields."
The analysis concluded: "The repeal may also mean that new gas field supply is discovered and developed, increasing supply further. However, this is unlikely to happen before 2035 and is outside the scope of this exercise."
As a result of the longer timeframe to see any significant boost to existing gas fields, the analysis says impacts on greenhouse gases are also smaller than previously estimated, in a climate analysis prepared in May.
"The key difference is the expected timing of when contingent reserves can be converted to supply. We have assumed that contingent reserves may extend the lifespan of existing fields but are not likely to significantly raise short-term production," said MBIE.
The analysis said in all scenarios, the modelling assumed gas prices would rise "to within the range of the cost of importing LNG".