The Government afforded itself ample wriggle room in international negotiations on carbon-dioxide emissions by committing NZ yesterday to cut up to a third of current levels by 2020.

It proposes to limit emissions to between 10 and 20 per cent below what they were in 1990, or take financial responsibility for the overshoot.

At the moment, gross emissions are around 24 per cent above 1990 levels, so the target amounts to a cut ranging from just under a quarter to more than a third from where they are now.

But it depends on a set of conditions that allow a lot of room for interpretation or judgment.

These include that other developed countries make efforts "comparable" to New Zealand's, that major developing countries (China and India) take action "commensurate with their responsibilities", that the global agreement "sets the world on a pathway to limit temperature rise to not more the 2 degrees C" and that there are acceptable changes to the international rules relating for forestry and land use change.

Climate Change Negotiations Minister Tim Groser said the target put New Zealand in a "credible" position, as other countries understood the particular difficulties we faced in reducing emissions when half of them come from agriculture and two-thirds of electricity generation is from renewable sources already. Whether the conditions were met would not be resolved at the climate change conference in Copenhagen in December, he said. "But I'm optimistic we will see some solid points of agreement."

The target range falls below the 25 to 40 per cent cut that the United Nations' Intergovernmental Panel on Climate Change has said is needed from developed countries as a whole by 2020, en route to at least an 80 per cent reduction by mid-century.

"This is tantamount to telling millions of people around the world that New Zealand does not care enough about their fate to make the cuts that are needed," Oxfam NZ executive director Barry Coates said.

Greenpeace climate change campaigner Simon Boxer said, "The Government says it agrees with the idea of keeping global warming below 2 degrees, but its target range doesn't give us even a slim chance of doing so."

Business groups, however, generally welcomed the conditionality hedging the target.

"It's significantly more ambitious than some major emitters like the United States," said Catherine Beard, executive director of the Greenhouse Policy Coalition, which lobbies for the big industrial emitters. "If we aren't moving in concert with other countries the cost goes up significantly."

But the Business Council for Sustainable Development said a more ambitious target might be required as the negotiations developed.

"If this is the offer for the Bonn talks [which began overnight] we will need a much better one by Copenhagen in December," said its executive director, Peter Neilson.

Labour spokesman Charles Chauvel said the target was a signal the Government was not serious about climate change, would not put in place domestic policies that would make much difference and would not pull its weight internationally.

Environmental Defence Society chairman Gary Taylor said New Zealand had positioned itself as a climate laggard and its international reputation would suffer.

But Prime Minister John Key said the target could be compared with 14 per cent below 1990 levels by Australia, 3 per cent below by Canada and the same as 1990 by the United States.

"It will mean higher costs for consumers and businesses, but 40 per cent would have cost jobs and Kiwi families' financial security."

Climate Change Minister Nick Smith said the Government was committed to an all-sectors trading scheme. "But agriculture remains a huge challenge."