Economics is not just about the allocation of scarce resources – how to ‘divide up the pie’. It is also about the creation of novelty, and the formation of new structures – how to make a pie in the first place. The new science of complexity, allied to old ideas of political economy, can help us understand how to create and change things quickly and at large scale. New economic thinking of this kind predicted the global financial crisis, but has barely begun to be applied to policy. It could transform the way we respond to climate change.