The climate change policies the two parties have recently released overlap a lot, in ways that distinguish them from National and the status quo.
But they are also at odds over which is the better way to put a price on emissions that will influence behaviour in the economy.
Labour wants to restore the emissions trading scheme (ETS), as designed by David Parker and enacted by the fifth Labour Government in the last few weeks of its ninth year in power, then promptly gutted by the incoming National Government.
But the Greens favour a tax on emissions, the proceeds of which would be used to plant trees on erosion-prone land, and the rest (most of it) recycled as an annual payment to everyone over the age of 18.Pigovian taxes (e.g. a tax on carbon emissions) and tradeable pollution permits (e.g. the emissions trading scheme) are essentially two ways of arriving at the same destination - a reduction in emissions. Consider the diagram below, which represents a simple model for the optimal quantity of pollution (or carbon emissions). The MDC curve is the marginal damage cost (the cost to the environment of each additional unit of carbon emitted) and is upward sloping - this is because at low levels of carbon emissions, there is relatively less damage because the environment is able to absorb it. The capacity for the environment to do this is limited, so as carbon emissions increase the damage increases at an accelerated rate. The MAC curve is the marginal abatement cost (the cost to society of each unit of carbon emissions abated, or reduced) and is upward sloping from right to left. This is because, as more resources are applied to reducing carbon emissions, the opportunity costs increase. This may be because less suitable resources (meaning more costly resources) have to begin to be applied to pollution reduction. The optimal quantity of carbon emissions occurs where the MDC and MAC curves intersect - at Q*. Having less carbon emissions than Q* (such as at Q1) means that MAC is greater than MDC. In other words, the cost to society of reducing that last unit of carbon emissions was greater than the cost in terms of environmental damage. Having pollution at Q1 must make us worse off when compared with Q*.
The diagram illustrates that there are two ways of arriving at the optimal quantity of carbon emissions. One way is to regulate the quantity of emissions to be equal to Q*, as you would in an emissions trading scheme. You allocate carbon permits equal to exactly Q*, and legislate that no one is allowed to emit carbon unless they have permits (and have appropriately large penalties in place for those that break the rules).
An alternative is to price emissions at P*, as you would through a carbon tax. If the price of emissions is P*, you will have exactly Q* emissions. This is because no one would want to emit more than Q*, because the MAC is lower than the tax they would have to may (so it is cheaper to abate one unit of carbon emissions than it is to pay the tax, so at quantities above Q* the quantity of emissions would reduce). Similarly no one would want to emit less than Q*, because the MAC is greater than the tax (so it is cheaper to emit one more unit of carbon and pay the tax, rather than pay the cost of abating that unit).
Which should we prefer - an emissions tax, or an emissions trading scheme? There are arguments for and against either (as I have noted before). Neither system is particularly flexible if new cleaner technology becomes available. Both provide incentives to reduce carbon emissions to Q* (and no further). Taxes may be less subject to corrupt practices (such as in deciding who would get any initial allocation of permits). Permits may be more efficient in the economic sense, since the emitters who can reduce their emissions at the lowest cost would sell their permits to those who can only reduce emissions at high cost.
Fallow doesn't conclude that either system is better though. However, one thing is clear, and that is that all countries doing nothing about carbon emissions is unambiguously worse than either system. And both emissions taxes and emissions trading schemes are better than old-school command-and-control regulation.