Arriving at an emissions target is a tug-of-war between what is necessary and what is possible.
The latter has proven the brawnier team.
"It comes down to a political judgment about what is achievable," said Climate Change Minister Nick Smith.
But while the recession changes a lot of things, it
does not change the laws of arithmetic or the laws of nature.
The laws of arithmetic dictate that the less done in the next 10 years the more will have to be done later to get global emissions down to the level they need to be in the long term.
And it is the laws of nature, still imperfectly understood, which determine what that level is - not us.
But politics is the art of the possible and too ambitious a near-term target would be a recipe for failure, recrimination and cynicism.
There are essentially three things New Zealand can do to meet its share of the international target to be negotiated in Copenhagen in December.
One is to physically reduce emissions - for example by putting more fuel-efficient vehicles on the roads, progressively retiring the Huntly power station's coal-fired turbines or giving dairy farmers incentives to use less urea.
The second is to plant a whole lot more trees, especially on erosion-prone hillsides.
The third is to buy carbon credits, arising from UN-certified emission-reducing projects in the Third World, on the international market. How costly an option that is will depend on the extent to which the Americans join the Europeans as buyers on that market.
There is a lot of politics in Washington and Copenhagen to go through before that is sorted out.
But the brutal arithmetic is that a target of 15 per cent (the mid-point of the target range announced yesterday) takes us to little more than two-thirds of what we emit now.
Achieving it will require bending what has so far been a relentlessly rising curve, and soon.
