ABSTRACT How does demand uncertainty affect firms' investment decisions? We examine this question in the context of electricity‐producing firms' planned investments in new power plants. We measure uncertainty about future electricity demand using plausibly exogenous variation in temperature projections across scientific climate models. The results show that uncertainty increases investment in power plants with flexible production technologies, while reducing investment in less flexible technologies. Overall, the net effect of uncertainty on investment is positive when firms have access to flexible investment opportunities. These findings are consistent with models in which production flexibility shapes the investment response to demand uncertainty.