Global warming may endanger the survival of tropical montane cloud forests, according to a new study published in Nature April 15. The forests, often located on mountaintops or ridgelines, rely on moisture from clouds to survive. A computer simulation study by Stanford biology doctoral student Christopher J. Still, Stanford biology Professor Stephen H. Schneider and Prudence N. Foster, an astrophysicist from the University of Tokyo, shows that increased temperature caused by doubling the level of carbon dioxide in the atmosphere may raise the altitude of clouds so much that they recede from mountaintops, in the process threatening complex ecosytems that contain many endemic species.