Whilst global environmental change in the 21st century will undoubtedly have direct impacts on built heritage, it will also have important indirect effects through its influence on microbial, plant and animal life on heritage sites. Environmental change will affect both the structure of biotic communities and the function of such communities. Both impacts will, in turn, influence the deterioration and conservation of heritage sites. Changes in precipitation will exert a major, but as yet poorly understood, control on heritage biotas, whilst changes in atmospheric composition may also be important. Climatic changes will cause range shifts for some taxa, further influencing community composition. Whilst there are many unknowns, making prediction difficult, some scenarios can be proposed based on ecological response to stress and disturbance. This approach indicates some ‘hotspots’ at risk of experiencing dramatic shifts in biotic communities and their impacts, which may switch from biodeteriogenic to bioprotective or vice versa. Such hotspots include vulnerable sandstone and limestone heritage structures in areas of the Mediterranean, Middle East, Caribbean and Southern Africa.