New Zealand promised on Sunday (October 31) to cut its net greenhouse gas emissions by half by 2030, upping its prior aims to halt global warming at the United Nations COP26 climate summit.

At the COP26 conference, which begins on Sunday evening in Glasgow, Scotland, leaders of the world's 20 richest countries are expected to accept the existential threat of climate change and take actions to curb global warming.

"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.

In a joint statement, Ms Ardern and Climate Change Minister James Shaw said the earlier objective was incompatible with global efforts to keep global warming to 1.5 degrees Celsius above pre-industrial levels.

New Zealand's previous goal was to reduce emissions by 30% by 2030 compared to 2005 levels.