The National Party will support the Government's Zero Carbon bill through its first reading in the House, despite outlining previously outlining "serious concerns".

However, no commitments have been made to support it at the second and third reading as it makes its way through Parliament.

Earlier this month, the Government unveiled details of the Zero Carbon Act.

It commits to what is called a "split target" – aiming to reduce all greenhouse gas emissions, aside from biogenic methane, to net zero by 2050.

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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 bill also commits to reducing gross emissions of biogenic methane to between 24-47 per cent below the 2017 levels, by 2050.

Speaking at the first reading of the bill today, National Leader Simon Bridges said National took climate change seriously and talked up the previous Government's record on renewable energy.

"I agree with Shaw that it is too important, economically, socially for petty partisanship."

National was happy with the split target but Bridges said he wanted to make it clear that the party had some "real differences" with the Government when it comes to the bill.

The main issue was with the methane targets, saying it will mean a significant amount of livestock culling across the country.

He said there were also issues to do with the "wider economic impact" of the bill.

Climate Change Minister James Shaw, who spoke before Bridges, said it was not alarmist to suggest that climate change was an emergency.

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"We ought to call it what it is … the world is on fire."

He said there was currently "climate crisis".

He thanked National for putting "politics to one side" in supporting the bill.

He said this shows climate change was too important for "petty partisan politics".

Prime Minister Jacinda Ardern acknowledged National for its support in the first reading and the party's "goodwill".

But she challenged Bridges on his comments about the economic cost, saying he was not taking into account the economic damage that climate change would have on New Zealand if no changes are made.

"Today we lay the foundation in the house – we take our nuclear-free moment so the next generation doesn't have to."

Although National welcomed the bill after it was unveiled, Bridges said the party had "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.

"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."

National has been working with the Government on the legislation for months.

When unveiling the legislation, Climate Change Minister James Shaw thanked National for their work on the bill.

Ardern has said she would prefer if the bill had bipartisan support.

Act, whose leader David Seymour has one seat in the House, said it would not be supporting the bill.