Tropical montane cloud forests are among the most vulnerable terrestrial ecosystems to climate change owing to their restricted climatic requirements and their narrow and fragmented distribution. Although 12% of Mexican cloud forest is protected, it is not known whether reserves will ensure the persistence of the ecosystem and its endemic species under climate change. Here, we show that 68% of Mexico's cloud forest could vanish by 2080 because of climate change and more than 90% of cloud forest that is protected at present will not be climatically suitable for that ecosystem in 2080. Moreover, if we assume unprotected forests are cleared, 99% of the entire ecosystem could be lost through a combination of climate change and habitat loss, resulting in the extinction of about 70% of endemic cloud forest vertebrate species. Immediate action is required to minimize this loss--expansion of the protected-area estate in areas of low climate vulnerability is an urgent priority. Our analysis indicates that one key area for immediate protection is the Sierra de Juárez in Oaxaca. This area supports many endemic species and is expected to retain relatively large fragments of cloud forest despite rapid climate change.