A United Nations review has found a large credibility gap between New Zealand's target for reducing greenhouse gas emissions by 2020 and the measures in place to achieve it.

"It could find no plan for two-thirds or more of what is required to meet the target," said the Sustainability Council's executive director, Simon Terry.

"And it voices 'great concern' about whether New Zealand will put measures in place in time to do so."

New Zealand has tabled an offer, albeit a highly conditional one, to the international climate negotiations to reduce its emissions by between 10 and 20 per cent from 1990 levels by 2020.

Compared with projections for where emissions would be by then without any official measures to reduce them, that would be a reduction of 36 million-42 million tonnes of carbon dioxide equivalent a year.

A UN expert review team said the emissions trading scheme, the main mechanism through which the Government aims to meet the target, is expected to reduce emissions by only 12 million tonnes a year by 2020 - only a third of the reduction needed to meet the less ambitious end of the target range.

The ETS is under review by a committee headed by former Labour Government minister David Caygill.

Among the questions it has been set are whether to extend the scheme to agriculture, which produces nearly half the country's emissions, by the current date of 2015, and if so under what conditions, and whether other measures to limit the initial impact of the scheme should be extended beyond their expiry date of 2013.

The UN expert team expresses "great concern" about the uncertainty this gives rise to about the future effectiveness of the ETS.

A spokesman for Climate Change Minister Nick Smith said the 2020 target was a "responsibility" target.

"This means that New Zealand can achieve this target by a combination of reducing its domestic emissions and paying for equivalent emissions reductions made in other countries. New Zealand's target is conditional on a comprehensive global agreement being reached and is comparable with the targets of our major trading partners."

Mr Terry's analysis concludes that some of the emissions reductions the Government is claiming for the ETS are, in any case, dodgy.

Most of the claimed reductions arise from the phasing out of coal-fired electricity generation, but the tonnages cited are far higher than those emitted by the only coal-fired power station at Huntly.

Mr Terry said there had been no serious proposals to build coal-fired power stations in recent times.

Dr Smith's spokesman said, "The 7.2 million tonnes of avoided energy emissions in 2020 is based against a hypothetical scenario in which there is no ETS in place. Under such a scenario, additional coal-fired generation would economically be the cheapest option to meet growing electricity demand."

The Government expects New Zealand to meet its emissions target under the Kyoto Protocol for the 2008 to 2012 period, but only because of offsetting credits for carbon taken out of the atmosphere by commercial forests planted in the early to mid-1990s.

Meeting Carbon Calendar
* New Zealand's offer in the global climate change negotiations is to reduce its carbon emissions by 10 to 20 per cent below 1990 levels by 2020. Emissions are currently about 20 per cent above 1990 levels and rising.

* A UN review has looked at where our emission are heading if nothing is done and the forecast savings from the emissions trading scheme. It says the ETS will only get us to a third of that target.

* The Government says if New Zealand falls short it can buy credits representing emission reductions somewhere else in the world - the climate doesn't care where the reductions take place.

* But such purchases are supposed to be "supplementary" to action at home.