New Zealand will ratify the Kyoto Protocol's Doha Amendment, as negotiators and world leaders meet in Paris to try to hammer out a new deal to reduce global carbon emissions.
Two years ago, the government refused to sign up to the amendment, saying New Zealand wanted to push for a more comprehensive agreement.
More on this fortnight's climate summit in Paris
The amendment would create a second commitment period from 1 January 2013 to 31 December 2020, and has to be ratified by three quarters of the 144 countries signed up to the Kyoto Protocol before it can take effect.
Climate Change Minister Tim Groser said New Zealand would ratify it, as it saw it as "critical for maintaining momentum in global climate change negotiations".
Out of those 144 countries, only 54 have so far ratified it - with New Zealand on board, that takes it to 55.
Mr Groser said ratification was a sign of good faith as New Zealand entered the lead-up to negotiations for a new agreement.
"While New Zealand made its commitment for this period under the United Nations Framework Convention on Climate Change (UNFCCC), the Kyoto Protocol's parent treaty, we want to support this amendment's entry into force.
"Supporting the amendment reinforces our commitment to the global effort to respond to climate change.
"It is also critical that New Zealand can influence decisions that may have significant long-term impacts on our economy, such as access to international carbon markets and accounting rules for the land sector," Mr Groser said.
Opening talks in Paris
Meanwhile, there have been a series of opening addresses at the UN talks in Paris - with heads of state and governments exhorting each other to find a common cause, ahead of a fortnight of bargaining to steer the global economy away from its dependence on fossil fuels.
Leaders from 147 nations, including New Zealand Prime Minster John Key, have addressed the meeting - known as COP21.
Labour climate change spokesperson Megan Woods, who is at the summit, said the leaders' push had met with a mixed response in Paris.
Some other countries and some non-governmental organisations (NGOs) were critical of the communique that had been released, she said.
"An NGO, the Climate Action Network, has just awarded John Key the 'fossil of the day', not because of the goals that were put out in the communique, but because of the domestic action on the ground in New Zealand.
"They say the actions in New Zealand don't match up with the rhetoric in the communique."
Green MP Julie Anne Genter is also in Paris.
It was surprising to hear Mr Key speak about the need for all countries to work together, to make real commitments, to get real outcomes, she said.
"There seems to be a huge disconnect between what he's saying here in Paris and what's actually happening home in New Zealand where, under his watch, pollution has increased and is forecast to continue increasing.
"There have been no policy announcements that would lead us to believe we could substantially reduce pollution over the next few decades."
New Zealand's latest commitment is to cut emissions by 30 percent below 2005 levels by 2030, or 11 percent below 1990 levels.
Ms Genter said that would not be enough. "There's been a group of international scientists, called Climate Trackers [Climate Action Tracker], who are quite independent and they've rated New Zealand's target as one of the worst of all countries signed up to similar targets."
Call to end fossil fuel subsidies
In his speech at the conference, Mr Key said there should be more of a push to get rid of fossil fuel subsidies.
New Zealand is one of 40 nations including Britain and the United States arguing the subsidies have to be phased out, but Australia is against the idea.
Mr Key said research showed phasing out the subsidies could reduce greenhouse gas emissions by as much as 10 percent.
Ms Genter said it was striking that, when making those comments, Mr Key said there was a need for courage and political will.
"I would say that's exactly what's needed home in New Zealand.
"He's on this working group looking at phasing out subsidies for consumers, while back in New Zealand we actually have a whole lot of subsidies and tax breaks for exploration and production of fossil fuels, which is actually even worse, I would argue."