Many mountain ecosystems are experiencing coincident increases in temperature, levels of atmospheric carbon dioxide (CO2) and atmospheric nitrogen (N) deposition. All are important controls on rates of plant growth, soil microbial activity, nutrient cycling, and stream N export. It is difficult for experimental studies to explore ecosystem responses to more than one or two treatments at plot, let alone catchment, scale. One might expect, however, ecosystems to respond differently to the combined global change drivers than to climate, CO2, or N alone. We explored this question for nine mountain catchments over the period 1980- 2075 with a simulation model.