We examine the effect of mandatory climate risk disclosure on insurers’ investment portfolios by exploiting the U.S. insurance industry’s adoption of the Climate Risk Disclosure Survey (CRDS), which mandates that qualified insurers report their climate risk. Using a staggered difference-in-differences research design, we find a significant post-adoption improvement in the environmental friendliness of the treatment insurers’ corporate investment portfolios. We also find that the CRDS’s positive effect on environmentally responsible investing is more pronounced when insurers face greater pressure to be more climate friendly. In terms of specific actions, we find that the treatment insurers reduce their holdings in firms with negative climate-risk-related news as well as in firms involved in the extraction of fossil fuels, and shift from  firms with high greenhouse gas emissions to firms with low greenhouse gas emissions. Finally, mandatory CRDS adoption is associated with a decline in the treatment insurers’ investment performance; this effect is concentrated among insurers that improve the environmental performance of their investment portfolio.