Climate Change and Non-mechanically Ventilated Historic Interiors

Concern over climate change has dominated our thinking about the global environment in recent decades. The impact on our heritage both indoors and outdoors can seem less significant and has not been part of the IPCC assessments. Increasing global temperatures, changed spatial and temporal patterns of rainfall and a decline in relative humidity are examples of the types of changes that could affect historic buildings. Relatively little has been published on the potential the changes in external climate compared with that indoors although some research, particularly in Europe has begun to address this. It suggests that while temperature may increase, relative humidity is likely to be more stable in historic buildings. Rainfall is localised and often needs to consider circulation patterns, so is harder to project into the future. Nevertheless there are likely to be changes in the amount of rainfall. In Europe a decrease in overall rainfall is often projected, but with changes in distribution, with potentially heavier rains in winter and intense downpours of summer rainfall.
The impact of these changes is likely to be seen indoors. The potential for increased presence of insects more typical of warmer climates might be realised if food and habitats remain available. Mould is likely to increase, although probably driven more by the increases in temperature than by changes in relative humidity. Higher temperatures could increase the sensitivity of materials such as historic paper to thermal decay. Climate cycles indoors with increased amplitude could impose stress on wooden objects and other organic materials. Indoor humidity control in buildings by conservation heating might be more difficult in a warmer world. The extremes of temperature outside might induce different visitor behaviour in historic interiors and the desire for comfort might demand more active control of indoor temperature.
The management of many of these potential problems may not be especially difficult as it would usually involve the thoughtful application of existing technologies. In general the need for regular maintenance might become even more important in the future. Government pressure to reduce energy demand is also likely to affect the way historic interiors are managed. The long time scales involved make climate change induced conservation issues easy to neglect in the face of more urgent problems, and also require a complex and strategic approach to planning and management.