One of the main principles for decision-making under uncertainty holds that we should diversify our risks. The principle of diversifying risk is most familiar from investment contexts, in which investors seek to spread investments across a range of companies, rather than placing all of their funds in a single stock. Diversifying risk improves prediction and reduces the likelihood that outcomes will be dominated by unforeseen effects. By contrast, failing to diversify risks increases the likelihood that there will be major, unforeseen systematic errors in our predictions. In this paper I defend the Diversify Risk principle against possible objections, and then consider its implications for how we ought to respond to climate change. I argue in particular that the principle should lead us to be cautious about technological, social or economic responses that are too large-scale or monolithic, and should lead us to favour 'portfolio' responses such as the 'stabilization wedges' approach. The principle also speaks in favour of market tools that encourage diverse smaller-scale forms of innovation. In the paper, I present these suggestions, and then draw out some of the reasons that it might be difficult to understand whether we have successfully diversified our risks in relation to climate change.
