A global climate change deal has been hailed in New Zealand as a historic step, but scientists and environmentalists say the deal now needs to be backed with action.

The Paris Agreement, signed by 197 countries yesterday morning (NZ time) after two weeks of negotiations, was described by Climate Change Minister Tim Groser as a "huge and historic step forward".

It is the first global agreement on climate change and all member countries are committed to limit global temperature rise to 1.5C this century.

Mr Groser, speaking to the Herald from Los Angeles, said countries' existing commitments to cut greenhouse gas emissions would lead to the planet warming by an estimated 2.7C to 3C this century.

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He said that under a new five-yearly review process in the agreement, New Zealand would come under huge pressure to strengthen its emissions reduction target in 2020.

"The whole idea of reaching this long-term goal is to progressively ratchet up each country's response and the New Zealand Government of 2020 will have that on their plate."

But in the meantime, he said, the Government did not need to change any policies as a result of the agreement.

"I don't mean that we just sit on our backside and do nothing. What I mean is we have the key elements in place."

New Zealand would continue to meet its international obligations by buying carbon credits and seeking cuts in the transport sector - partly through policies which were soon to be announced and which encouraged electric car uptake.

Climate scientist Professor James Renwick, from Victoria University, said now a global agreement had been reached, "this is where the work really begins".

The goal of limiting warming to 1.5C was "daunting" because the world was already well on its way to this level of temperature rise, he said.

Professor Renwick said New Zealand had an obligation to make actual cuts to its emissions instead of paying for its pollution through carbon markets. He said it was difficult to cut agriculture emissions, which make up nearly half of New Zealand's total emissions.

To meet its obligations, the Government should seriously consider scrapping oil exploration plans, expand renewable electricity generation from 80 per cent to 100 per cent, and create detailed policies for cleaner transport systems.

"The way the New Zealand Government's operated on this, I'm not hopeful that New Zealand will be any kind of a leader on this at all," he said.

Centre for Energy Research director Ralph Sims, of Massey University, said the biggest changes in Paris occurred outside of government negotiations. He witnessed huge momentum among banks, businesses, financiers, cities, and NGOs towards lower-carbon economies.

But in New Zealand, where coal-fired plants were still being opened, there was a risk of falling behind, he said.

What is the Paris Agreement?

The first global agreement to cut greenhouse gas emissions and avoid the worst effects of climate change. It has been signed by 197 countries including New Zealand.

What does it do?

Commits nations to keep global temperature rise below 2C this century, with a target of 1.5C. Sets a target of zero net emissions between 2050 and 2100. They will have to review and perhaps strengthen their commit-ments every five years.

What does it mean for New Zealand?

Will be obliged to reduce its greenhouse gas emissions. Nearly half of NZ's emissions come from agriculture, which are difficult to reduce, so cuts will have to come in the energy and transport sector and by buying carbon credits from offshore markets. NZ will also have to consider a greater emissions reduction target in five years.