Biogenic methane – the emissions created from livestock such as sheep and cattle – is not completely exempt, as the bill commits to reducing it to 10 per cent below the 2017 levels by 2030.
The legislation only sets the goals – it does not say how the Government should get to that level.
The Climate Change Commission, which the bill will also establish, would help the Government set ways of meeting the targets.
The bill also commits to reducing gross emissions of biogenic methane to between 24-47 per cent below the 2017 levels, by 2050.
This means there will need to be significant changes to New Zealand's agriculture sector if the target is to be met.
Farming lobby group Federated Farmers said the goal is extreme and would send the message to farmers that New Zealand is prepared to give up on pastoral farming.
But, speaking to media at the unveiling of the legislation, Shaw said this would not mean a culling of livestock would be needed to reach the goals.
He said the focus would instead be on developing technology to reduce emissions. Much of that technology, he said, is not yet available.
"If we waited to invent the technology to get to the moon before we set the target of getting there, we would have never of got there," he said.
"Yes, it is aspirational and no we don't actually currently have today everything that we need to get us there but we do have the things to get us started."
He used the example of the steel production sector, which emits a large amount of carbon dioxide.
"Currently there isn't a substitute technology in steel production – we're going to have to create that during the course of the next 30 years to hit the target on the CO2 side."
Ardern said there were many ways to reduce the agricultural methane emissions without culling cattle.
"We can change the way they graze. You can change what they eat."
She said the Government had already invested $20 million into agricultural research and development.
But both she, and Shaw, agreed more was needed.
"Yes, we have set an aspirational, albeit a provisional, [goal]. Because we are absolutely accepting in setting the band that we have, that we need that further scientific evidence around precisely where we need to head on biogenic methane."
Deputy Prime Minister Winston Peters said the agriculture sector would be able to meet the Government's targets.
"I believe that, with our help, which is serious financial backing to the on the farm operation and the research level that we will put into it, they will meet those targets easily."
Asked if that meant the Government would be spending more on research and development, Peters said "precisely".
"But we're going to consult with the farming industry and see whether they want it on the farm, or part on the farm and into research."
The bill has been the subject of intense negotiations for months.
Based on the original estimates of its progression through the Parliamentary system, the bill was meant to be introduced into the House October last year and in force last month.
That timeframe, however, was pushed back to accommodate for more negotiation time.
National today welcomed the bill and its leader, Simon Bridges, said the party is happy with the net-zero target and the separate treatment of methane.
But National has "serious reservations" about the expected rate of the gross emissions reductions of biogenic methane to between 24-47 per cent below the 2017 levels, by 2050.
Bridges was not convinced that this range meets National's test, in terms of science, economic impact, or global response.
"New Zealand has been a global leader in sustainable agricultural production. For this leadership to be enhanced the sector must continue to embrace change, but this target goes beyond credible scientific recommendations."
As to whether or not National will support the bill in the first reading, a spokesperson said that will be discussed in caucus.
Shaw said the bill was something he thought could have the support of National in the House.
NZ First Leader Winston Peters was pleased with the bill and said his party had the "agriculture sector's interests at heart".
"In negotiations, New Zealand First sought to balance the interests of the agricultural sector and the need for the Government to take strong action and show leadership on climate change."
He said the Government was committed to assisting the farming and agriculture sector through this transition period.
But Act Leader David Seymour said the bill would not change the climate in a significant way, as the country only makes up 0.17 per cent of global emissions.
"If we are forced to make significantly deeper emissions cuts than our trading partners, we will simply impoverish ourselves and push economic activity to other countries."
