The National Party is supporting the Zero Carbon Bill through its final reading in Parliament.

National leader Simon Bridges said while National supported it, he's committing to improving the Bill further should the Opposition earn the right to govern in 2020.

"National proposed a series of changes that would have ensured the Bill is in line with National's climate change principles of taking a pragmatic and science-based approach, but unfortunately the coalition Government voted down all of our amendments."

The legislation didn't need National's support to pass because Labour, the Greens and New Zealand First make a majority. But Climate Change Minister James Shaw has been working to get National's support.

Bridges said should National be elected in 2020, it will be up to the Climate Change Commission to decide on the methane reduction target, continuing its pushback against the 24-47 percent reduction by 2050 in the current Bill.

DairyNZ is calling for the 2050 target to be up to 24 percent, and "regularly reviewed whilst the science remains unsettled".

Bridges said National would also make clear the stated aim of the Paris Agreement - which National signed New Zealand up to in 2016 - is for greenhouse gas reduction to occur in a" manner that does not threaten food production".

The Paris Agreement recognises the "fundamental priority of safeguarding food security" and says policies addressing climate change should "not threaten food production".

Federated Farmers says the 2050 24-47 percent reduction target for biogenic methane "remains eye-wateringly hard for farmers to achieve".

National would also change the Bill to ensure the commission considers the "appropriate use" of forestry offsets, and "has regard for the carbon sink represented by crops, riparian planting, and other farm biomass".

The emissions budgets would be split between biogenic methane and carbon dioxide as recommended by the Parliamentary Commissioner for the Environment.

And the Bill would include a greater commitment to investment in innovation and research and development to find new solutions for reducing emissions.

"We have taken a bipartisan approach to climate change but we will continue to fight for the changes we think will make the law better," Bridges said.

"Should National earn the right to govern in 2020 we will make these changes in our first 100 days in office."

So far, ACT is the only party that hasn't supported the legislation.

"The Zero Carbon Bill also gives the Climate Change Minister unconstrained power over the New Zealand economy," ACT leader David Seymour said.

Seymour is pushing back against a requirement in the legislation that requires emissions offsets to take place in New Zealand.

He proposed an amendment that would have allowed New Zealanders to achieve emissions reductions at the lowest possible cost by purchasing overseas units as well as domestic units.

"It shouldn't matter if trees are planted in Northland or in the Amazon."

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