A 15 per cent target would be the equivalent of eliminating within 10 years all emissions from transport and electricity generation. Photo / Martin Sykes

A 15 per cent target would be the equivalent of eliminating within 10 years all emissions from transport and electricity generation. Photo / Martin Sykes

Over the next few days the Government will make one of the biggest calls of its term in office, announcing a greenhouse gas emissions target for 2020.

It has to have a target to take to Copenhagen in December when the world gathers to negotiate a new climate treaty to follow the Kyoto Protocol.

The sort of number the Government has been directing our attention towards, in a non-committal way, is a 15 per cent cut from 1990 levels. That would also be 15 per cent below the current commitment under the Kyoto Protocol.

But as New Zealand's gross emissions are 24 per cent above 1990 levels, such a target would be a cut of nearly a third from where we are now.

It would be the equivalent of eliminating, within 10 years, all emissions from transport and electricity generation, and then some. Transport accounts for 20 per cent of national emissions, the electricity sector 9 per cent.

Alternatively it would be equivalent to reducing by two-thirds emissions from pastoral farming. Agricultural emissions in the form of methane and nitrous oxide from the bodily functions of cattle and sheep are 48 per cent of the national total.

"The nightmare for the Government is that even what looks like a very modest target is incredibly challenging, because we are starting 24 per cent behind the eight ball," says Climate Change Minister Nick Smith.

At the Bali climate change conference in late 2007 developed countries agreed to the notion of "comparability of effort" but there is no agreement about how to define that.

Nor will there be in Copenhagen, says Trade and Climate Change Negotiations Minister Tim Groser, but he expects "some sense of what is reasonable" to emerge from the hurly-burly of the negotiations.

The case New Zealand will be making for a target at the lenient end of the range for developed countries goes like this: While our emissions have grown comparatively rapidly since 1990 that is partly because the population has too. In that respect we are more like Australia and the United States than Europe or Japan.

Per capita emissions are also near the high end of the international range. But that reflects the fact that nearly half of them come from farming and most of the food New Zealand produces is exported.

On a trade-adjusted basis, where you deduct the emissions embedded in exports and add back imported emissions, they are more respectable.

Then there is the ability to pay. New Zealand sits in the bottom third of the OECD in terms of per capita gross domestic product, somewhere between Spain and Greece and well below the income levels of the Americans, northern Europeans or Japanese.