Slashing pastoral stock numbers by up to 35 per cent has been suggested among ways to push New Zealand's greenhouse gas emissions down to zero by 2100.

A cross-party group of MPs have commissioned UK consultants Vivid Economics to look at the options, which have been presented as four bold scenarios for the country in a new report launched today.

Under the first scenario, the country would further slash the emissions intensity of its economic activity through technological advances, such as cost reductions in electric vehicles for freight, electric heating technologies for high temperature applications and a vaccine to reduce methane emissions from pastoral agriculture.

This would be accompanied by a structural shift away from pastoral agriculture - with animal numbers around 20 to 35 per cent lower than today - to less emissions-intensive activity.

The country would instead support a diverse range of land uses, including horticulture and crops, alongside extensive planting of forests, covering an extra million hectares of land by 2050.

This scenario could result in a 70 to 80 per cent reduction in net emissions compared with current levels, however the authors said this option still relied upon breakthroughs like high-grade heat and non-passenger transport, along with extra tech in the agriculture sector.

Under a second scenario, an extra 1.6 million hectares of forest planted by 2050 would "substantially reduce emissions" - a 65 to 75 per cent reduction - and provide opportunities in a significantly enhanced forest products industry.

"However, changed land uses may require a difficult transition for rural economies, as well as represent a lost opportunity to reintroduce native habitat."