Green Party spokesman Kennedy Graham said using 2005 as a benchmark was "pure spin". Once the usual benchmark of 1990 was considered, the reduction was paltry, he said.
Mr Groser said the 2005 benchmark aligned with big players such as the US and Canada. In a consultation paper, the Ministry for the Environment estimated raising the target from 5 per cent to 10 per cent would cost households $30 more a year. Raising it to 40 per cent would cost households about $530 a year.
But environmental advocates said the ministry had failed to include the cost of not acting on climate change. A 2013 drought fuelled in part by man-made climate change, for example, cost the New Zealand economy more than $1.3 billion.
Mr Groser said there were fewer opportunities for New Zealand to immediately reduce its emissions because about half its pollution came from producing food "for which there aren't yet cost-effective technologies to reduce emissions".
In 2013, New Zealand produced 400 tonnes of CO2 equivalent per unit of GDP. Of this total, 48 per cent came from agriculture and 22 per cent from transport.
Youth climate change organisation Generation Zero said 69 per cent of 15,000 submitters had wanted a target of 40 per cent or higher.
Emission targets
2020: 5% reduction on 1990 levels
2030: 11% reduction on 1990 levels (or 30% reduction on 2005 levels)
2050: 50% reduction on 1990 levels