Choosing a discount rate, of course! Great post on New York Times Upshot blog by Michael Greenstone of the University of Chicago. He talks about the “social cost of carbon,” a critical element in evaluating climate policies. The great uncertainly surrounding climate effects in the distant future suggests a lower discount rate, and therefore a higher value to current actions that may not bear fruit for many years. This is applicable to a broad range of educational, social and health issues throughout the nonprofit sector. If the risks, say, 20 years from now are potentially very high, you may want to hedge your bets in spite of the uncertainty.