So far, I have left four loose ends in this book. Here I tie them up.

In Chapter 3 I concluded that the countries most enthusiastic about slowing global warming are likely to adopt quite varying national strategies for regulating emissions. It is unlikely that any of them will adopt simple economy-wide cap and trade programs that would let them make credible international promises to regulate their emissions at particular levels. That conclusion points to the need for flexibility when these countries negotiate their international commitments and also suggests that those commitments could become quite complex as these governments tighten the screws and implement highly diverse policies whose exact impact on emissions are hard to measure. But I have not shown how international negotiations can manage that complexity.

In Chapter 4 I argued that the success of efforts to slow global warming will hinge on engagement of countries that are, today, reluctant to spend their own resources on controlling emissions. I showed that these countries could make a much bigger dent in emissions with very little extra effort but that the current system of incentives – the Clean Development Mechanism (CDM), notably – is not well matched to the real barriers that slow action. But I have not shown how a different system of incentives could work.

In Chapter 5, I showed that efforts to control emissions must be married to an active technology policy. I also showed that only a handful of countries need be engaged.