Projected changes in global climate have substantial ramifications for biological diversity and the manage- ment of natural areas. We explored the potential implications of global climate change for biogeographic patterns in the Greater Yellowstone Ecosystem by using a conceptual model to compare three likely climate scenarios: (1) warmer and drier than the present; (2) warmer and drier, but with a compensating increase in plant water use efficiency; and (3) warmer and wetter than the present. The logical consequences of each scenario are projected for several species and community types chosen to represent a range of local cli- mate conditions and biotic responses in the Greater Yellow- stone Ecosystem. The upper and lower timberline appear to be particularly sensitive to climate change. The upper timberline is likely to migrate upward in elevation in response to temperature changes, whereas the lower treeline may re- treat under drier conditions or move down slope under wetter conditions. In all scenarios, the extent of alpine vegetation in the ecosystem decreased. Climate-induced changes in the fire regime in the Greater Yellowstone Ecosystem would probably have substantial consequences for the extent and age-class distribution of forest communities. Alterations in the distribution and extent of grassland communities would affect the populations of large ungulates. Our analyses suggest directions for establishing long-term measurements for the early detection of responses to climate change.