A cornerstone of the Labour-Green post-election deal, the legislation will enshrine net zero emissions by 2050, with an independent Climate Change Commission installed. Methane gases, primarily emitted by agriculture in NZ, will need to reduce by 10% by 2030 under the bill.

Read the Spinoff interview with climate change minister James Shaw here.

Almost a year after it was originally slated to appear, the Zero Carbon Bill has been released today. The legislation, the first listed policy pledge in the confidence and supply deal signed by Labour and the Greens after the 2017 election, lays out the route to net zero emissions by 2050 and establishes an independent Climate Commission to police that transition.

Limiting climate change to no more than 1.5 degrees Celsius over the next 30 years becomes a legally binding objective under the bill.

One of the stickiest elements in developing the bill has centred on the way methane is factored in. Methane gas, a massive part of New Zealand’s emissions profile, mostly comes from agriculture, specifically via belching livestock.

The bill sets out a “split gases approach”, meaning that carbon dioxide and nitrous oxide (long-lived gases) and methane (short-lived gases) will fall into separate columns. It sets a target for 10% reduction in methane emissions by 2030, and “aims for a provisional reduction ranging from 24% to 47% by 2050”.

While methane is short-lived in the atmosphere compared with carbon dioxide, it has a markedly greater short-term impact. Climate scientists have warned that methane emissions can have powerful exacerbating effects as the planet teeters on the brink of climate change tipping points.

The target range, which came in for immediate criticism from farmers’ groups, will be reviewable by the new independent Climate Change Commission which will issue five-yearly “emissions budgets”.

According to a recently published Greenhouse Gas Inventory report, New Zealand’s net emissions increased by 65% from 1990 to 2017. After offsetting, gross emissions had risen by 23% since 1990.

The prime minister will tomorrow give a speech at the Just Transition Summit in Taranaki outlining the measures that will assist regions and industries most affected by the bill.

Rather than being a free-standing bill, the measures are framed as an amendment to the existing climate change act, as the Climate Change Response (Zero Carbon) Amendment Bill. The legislation will be tabled in parliament today, with a view to being enacted by the end of the year.

The bill establishes a legal requirement for the government to plan how it will ensure that different regions and sectors, as well as iwi, are prepared to adapt for the impact of climate change.

Jacinda Ardern said: “We’ve built a practical consensus across government that creates a plan for the next 30 years, which provides the certainty industries need to get in front of this challenge.” Speaking alongside James Shaw in a press conference at the Beehive, she paid tribute to the climate change minister and Green co-leader, for whom the legislation was the culmination of “a personal 20 year journey”.

Shaw credited climate protests for helping to lend momentum. “In March this year, tens of thousands of New Zealand school students went on strike to protest the lack of decisive action on climate change. We hear them. The Zero Carbon Bill outlines our plan to safeguard the future that those school students will inherit,” he said.

“The critical thing is to do everything we can over the next 30 years to limit global warming to no more than 1.5 degrees Celsius and the Zero Carbon Bill makes that a legally binding objective.”

Shaw told media that while the 10% methane cut by 2030 was “a stretch target”, the scientific advice – drawn from the findings of the IPCC – was that it was manageable and would not require, for example, a cull of livestock. “We already have the technology, business models and tools available to us to make those reductions,” he said.

He rejected suggestions that the agricultural sector had been unfairly targeted. “There are sectors that are going to have to work a lot harder than agriculture to hit that target.”

Shaw acknowledged the National Party for its “constructive” engagement on the consultations around the bill, but there was no sign of an endorsement from the opposition. “They only got the bill on Monday, so they probably need a little bit of time to decide whether they can support it,” he said.

In a statement, the National Party said that while it welcomed the proposed amendments, they had “serious reservations about the expected rate of reduction for methane”. Simon Bridges said: “We are not convinced that the proposed 24-47% reduction for methane meets our test in terms of science, economic impact or global response.”

Generation Zero, the youth organisation credited with setting a template for the law in the leadup to the last election, said the bill was worth celebrating, but it was “highly critical” of the decision to wind the legislation into the existing climate change law.

“The Zero Carbon Act was designed to provide long-term certainty and political stability,” said spokesperson Lisa McLaren. “It needs to sit above specific policies like the ETS [Emissions Trading System] that are regularly reviewed and changed.”

Beef and Lamb New Zealand said the methane approach made unfair demands on farmers. “It’s unreasonable to ask farmers to be cooling the climate, as the government’s proposed targets would do, without expecting the rest of the economy to also do the same,” said a spokesperson.

“Beef + Lamb New Zealand is calling for a fair approach, where each gas is reduced based on its warming impact. An equitable approach requires carbon dioxide and nitrous oxide to go to net zero, and methane to be reduced and stabilised by between 10-22%.”

Expectations for bold legislation were heightened by the prime minister’s famous declaration during the election campaign that climate change was her generation’s “nuclear-free moment”. In an interview with the Spinoff in October last year, however, Ardern said she had “upgraded” that position, because she did not see the same level of national unity around climate change that there had been around nuclear-free New Zealand. Then, “we were unified”, she said. “What we’re doing on climate change – it is just that much harder, because it’s a call to action for everyone. And so I’m hoping we can get to the place of having that same unified moment that we had around nuclear free for climate change.”

The climate bill caps a busy few weeks for coalition wrangling in what the prime minister has christened “the year of delivery”. The Greens were dismayed, and NZ First delighted, by the announcement that plans for a capital gains tax would be jettisoned. Many Green Party stalwarts were disappointed, too, by the limited promises of action in response to recommendations late last week from the Welfare Working Group. Yesterday saw details of the referendum on legalising cannabis revealed.