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Climate Action Tracker says the target falls short of its share of the international effort required. It is a grouping of four independent European research organisations: Climate Analytics, Ecofys, New Climate Institute and the Potsdam Institute for Climate Impact Research.
It has been rating commitments being tabled for the Paris conference in December intended to thrash out a comprehensive agreement to curb emissions between 2020 and 2030.
New Zealand's provisional target is to reduce emissions to 30% below 2005 levels by 2030 which is equivalent to 11% below 1990 levels.
"New Zealand's climate target shows it's far from doing its fair share, and is anything but ambitious," Bill Hare, chief executive and senior scientist at Climate Analytics, said.
If most other countries were to follow New Zealand's approach, global warming would exceed 3degC or 4degC - making a world that would see oceans acidifying, coral reefs dissolving, sea levels rising rapidly, and more than 40% species extinction.
The CAT report is critical of New Zealand's approach to carbon accounting.
"While most other governments intend cutting emissions, New Zealand appears to be increasing emissions, and hiding this through creative accounting. It may not have to take any action at all to meet either its 2020 or 2030 targets," Mr Hare said.
"If New Zealand applies the rules it is proposing to use after 2020 to account for its Kyoto surplus and forestry credits, its overall agriculture, energy, waste and industrial greenhouse gas emissions could increase to 11 percent above 1990 levels by 2030."
Climate Action Tracker's analysis concludes that, based on current policies, New Zealand's emissions per capita, while likely to remain stable at around 17 tonnes of CO2 equivalent or decrease slightly, are set to surpass those of the United States by around 2025.
Emissions of methane and nitrous oxide from livestock are around half of national emissions. But emissions from transport and industrial processes have been growing fastest since 1990.
"Whilst New Zealand argues that agricultural emissions are hard to deal with, and there is some merit to this, its other sources of emissions growth can readily be addressed with appropriate policy frameworks and technologies," the CAT report said.
"There are no policies in place to address the fastest-growing sources of emissions in New Zealand from transport and industrial sources. For the energy system, whilst it is predominantly hydro and renewables, there is potential for further increasing renewable energy, and improving efficiency on the user end."
It also points out, as domestic critics of the target have and as Climate Change Minister Tim Groser has conceded, that it does not put New Zealand on a direct, straight line path to its longer-term goal of a 50 per cent reduction by 2050, unlike other major economies such as the European Union or the United States.
"New Zealand's climate policy is projected to head in the opposite direction from the world's biggest emitters such as China, the United States and the European Union," said Professor Kornelis Blok of Ecofys.
"It has taken little or no action on climate change since 2008 - except for watering down its ETS - and we can find no evidence of any policies that would change this."