GLASGOW (REUTERS) - New Zealand pledged on Sunday (Oct 31) to reduce its net greenhouse gas emissions by 50 per cent by 2030, toughening at the start of the United Nations COP26 climate conference its previous ambitions to limit global warming.

Leaders of the 20 richest countries are expected to acknowledge the existential threat of climate change and take steps to limit global warning at the COP26 summit starting on Sunday evening in Glasgow, Scotland.

"While we are a small contributor to global emissions, as a country surrounded by oceans and an economy reliant on our land, we are not immune to the impact of climate change, so it's critical we pull our weight," Prime Minister Jacinda Ardern said in a statement.

Ms Ardern and Climate Change Minister James Shaw said in their joint statement that the previous target was not consistent with global efforts to limit global warming to 1.5 deg C above pre-industrial levels.

New Zealand's previous target was to bring emissions to 30 per cent below 2005 levels by 2030.

The 2015 Paris Agreement committed signatories to keeping global warming to "well below" 2 deg C above pre-industrial levels, and preferably to 1.5 deg C, but carbon levels in the atmosphere have since grown.

"This decade is make or break for the planet," Mr Shaw said in the statement.

"To stand a chance of limiting global warming to 1.5 deg C, the science shows we now have about eight years left to almost halve global greenhouse gas emissions."

The New Zealand government has introduced several policies to lower emissions during its second term, including promising to make its public sector carbon-neutral by 2025 and buy only zero-emissions public transport buses from the middle of this decade.