Most forecasts for the Copenhagen summit on climate change  - which opens today - are decidedly gloomy. The Potsdam Institute for Climate Impact Research recently released a study condemning the emissions cuts currently proposed, many of which may well fail to materialise, as inadequate to prevent a temperate rise of three and a half degrees centigrade by the end of the century. Any such rise would leave large parts of the world barely habitable.

Lord Stern - he of the Stern Report - is only marginally more optimistic, having decided that global temperatures will increase by two degrees even if each country adopts the most ambitious targets it has proposed. Here in the present, the news is not much better: the Australian senate recently rejected Kevin Rudd's cap-and-trade plan; it is not clear that Barack Obama's similar bill has the votes to pass; and significant polluters like Canada and Russia have yet to make serious commitments. 

If a meaningful global deal is not forthcoming, what should committed individual countries such as the UK do? Over at openEconomy, Simon Zadek recently argued that we should not let a global deal become an all-consuming goal which gets in the way of the more realistic alternative: a patchwork approach involving unilateral actions by individual nation states. The EU in general and UK in particular have shown genuine leadership on such an approach, for which we can give ourselves a rare, deserved pat on the back (while remembering that it is very easy for governments to commit their countries to such-and-such a reduction in emissions by 2050, since they will not be around to suffer the consequences). It has also been given new momentum by commitments from China and India.

The classic argument against purely local action on climate change is that it is a global problem that requires a global solution, and that the pay-off of any one state's contribution to solving it will be dissipating across the world, with that country having little to show for it - precisely the sort of situation which leads to the problems of game theory. The best known such problem is the notorious prisoners' dilemma: a criminal duo are separated for interrogation and offered freedom in exchange for implicating the other party, but it will only be granted if the other one stays silent; if both snitch, they will get light sentences, whereas if neither accepts their sentences will be yet lighter, though only by a bit. It is in their interests if both keep schtum, but since neither knows what her accomplice will do, they may well reason that they are better off implicating them regardless of whether they stay loyal.

One problem with applying this otherwise quite convincing line of reasoning to unilateral action on climate change is that states' decisions are unlike those of the criminals in that they are not independent of those of other 'players' in the game, because they can see what these decide. One of the central rationales for unilateral action on climate change relies on this: this is, of course, the argument that it stands a chance at influencing other states both by serving as an inspiration and by providing political cover for them (a favourite argument of foot-draggers being that their nation should not shoulder the burden of combating global warming while others, without whom any hope of success is anyway vanishingly small, do nothing).

Even when individual action can influence others to take the win-win choice, prisoners' dilemma-style reasoning sometimes wins out. A famous historical case of this is the tragedy of the English commons. This communal plot of land was open to all, and consequently suffered from overgrazing as each peasant decided that he might as well use the land to its fullest regardless of whether his neighbours did the same. What is relevant to the case of climate change is that this attitude might have been mistaken: perhaps some villagers could have saved the commons by setting a good example and establishing norms for its use.

Whether this is so for states that take the lead on climate change depends on what influence they can reasonably expect to have. It is fashionable to be pessimistic here, but there have actually been encouraging signs: the EU's adoption of a cap and trade system has led the Democrats to make serious efforts to establish one in the US, and even previously recalcitrant nations such as India and China have recently changed their tune. On both sides of the Atlantic, there has been a resurgence of interest in 'border tax adjustments' - climate tariffs, effectively. Talk of these understandably makes free traders wary, but there is at least some economic rationale for them, and they are the perfect example of a unilateral action with outward-facing teeth. They also appeal to national electorates more than the bitter medicine normally associated with climate change mitigation does.

A unilateral approach to climate change is by no means hopeless then, even if it must ultimately be accompanied by concerted international action. Those of us who care about this issue should keep up the pressure on Ed Milliband and Labour, and then hold the Conservatives to their green promises should they win power next year. The failure of the rest of the world to deal seriously with the climate crisis is no excuse for inaction on our part.